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Supplementation of 1alpha-hydroxycholecal-ciferol (1alpha-OHD(3)), phytase, and Ca levels has been shown to influence phytate P utilization. Two experiments were conducted with 1- to 16-d broilers to investigate the interactions between the effects of 1alpha-OHD(3), phytase, and Ca on phytate P utilization. In experiment 1, the birds were randomly allocated to 13 treatments with 6 levels of 1alpha-OHD(3) from 0 to 11microg/kg, with and without 500 U/kg of phytase supplemented to P-deficient diet. A positive control diet, adequate in Ca and P, was included. In experiment 2, a 3-dimensional rotatable design with 5 levels each of 1alpha-OHD(3), phytase, and Ca was implemented. Supplementation of 1alpha-OHD(3) and phytase increased phytate P utilization, as indicated by an increase in bone ash, phytate P disappearance, and BW. In experiment 1, no interaction between the 1alpha-OHD(3) and phytase effects was determined for any criteria, except for the incidence of P rickets. However, the second experiment showed that there were interactions between the 3 factors (1alpha-OHD(3), phytase, and Ca). The probabilities that observed variation in the 3-way interaction for measured criteria that were due to chance are: BW gain = 0.1364, G:F = 0.11, bone ash percentage = 0.0278, milligrams of bone ash/tibia = 0.0909, Ca rickets = 0.9394, P rickets = 0.4892, tibial dyschondroplasia = 0.5927, and phytate P disappearance = 0.1126. The equations obtained from the regression models were used to generate contour-surface plots. The percentage of bone ash data indicated that low Ca, high phytase, and high 1alpha-OHD(3) levels were needed to optimize phytate P utilization. The results of this study show that this experimental design may be utilized to identify the best levels of nutrients to add to a diet where complex 3-way interactions exist affecting several criteria. The equations may be used to optimize performance based on desired levels of performance and the costs of the inputs.

An investigation was conducted to study insulin-like growth factor (IGF)-I, IGF-II, insulin, glucagon, leptin, triiodothyronine (T(3)), and thyroxine (T(4)) levels in a chicken population divergently selected for P bioavailability (PBA). There were differences in growth and feed efficiency between the 2 lines. Concentrations of IGF-I, IGF-II, and T(3) were significantly greater in the high PBA line compared with the low PBA line, whereas the reverse was true for glucagon. There were no correlations between IGF-I and II and PBA in either line, suggesting that the line differences may be the result of factors other than PBA. Glucagon and IGF-I have different relationships with feed conversion ratio in the high PBA line compared with the low PBA line. There was a significant correlation between PBA and T(3) in the low line and between PBA and T(4) in the high PBA line. Thyroid hormone levels may be an indirect indicator of PBA in growing chickens. The genes in the thyroid hormone pathway may be key in the identification of genes associated with PBA.

Two experiments were conducted to determine that variation in broiler P utilization is due to breeder age and egg storage time. Experiment 1 was conducted with chicks hatched from eggs laid by Ross x Ross 308 breeders (27 vs. 61 wk old) and stored for 0 or 10 d. The age of breeders had significant effects (P < 0.05) on 0 to 16 d chick growth (379 +/- 18 vs. 308 +/- 19 for 27- and 61-wk-old breeders, respectively). The longer egg storage time of chicks from older breeders resulted in higher P rickets scores and incidence, but longer egg storage time of chicks from younger breeders resulted in lower P rickets score and incidence (significant interaction, P = 0.0455). The longer egg storage time of chicks from older breeders resulted in lower bone ash (%), and the longer egg storage time of chicks from younger breeders resulted in higher bone ash (%). Experiment 2 was conducted with chicks hatched from eggs laid by Ross x Ross 308 breeders (26 vs. 60 wk old) and stored for 0 or 10 d. The diets were P deficient and with or without 5 microg/g of 1alpha-OH cholecalciferol (1alpha-OH vitamin D(3)). Breeder age had significant effects (P = 0.0003) on 0 to 16 d chick growth (272 +/- 7 vs. 339 +/- 8 for 26- and 60-wk-old breeders, respectively) and chick mortality (P = 0.0134). The P rickets score increased with breeder age (P = 0.0186) and egg storage time (P = 0.1057). The factors influencing the incidence of P rickets in broilers should include breeder age and egg storage time as well as genetics and dietary levels of Ca, P, and vitamin D activity of the P-deficient diets.

Supplementation of some organic acids to a P-deficient diet has been shown to improve phytate P utilization. Two experiments were conducted from 0 to 16 d in battery brooders to determine the effect of various organic acids supplementation on phytate P utilization. In both experiments, birds were fed P-deficient corn and soybean meal-based diets. In experiment 1, citric acid, malic acid, fumaric acid, and EDTA were supplemented. Experiment 2 had a 2 x 2 factorial design with 2 sources of Met, 2-hydroxy-4-(methylthio) butanoic acid (HMB) and dl-Met, with or without 500 U/kg of phytase. In experiment 1, the addition of citric, malic, and fumaric acids increased percentage of bone ash, but only the effect of citric acid was significant. The addition of citric and malic acids also significantly increased the retention of P and phytate P (P<0.05). In experiment 2, the addition of phytase to the diet significantly increased 16-d BW gain, feed intake, percentage of bone ash, milligrams of bone ash, phytate P disappearance, and decreased the incidence of P-deficiency rickets. Methionine source did not affect 16-d BW gain, feed intake, feed efficiency, milligrams of bone ash, or P rickets incidence. However, the birds fed HMB had a higher percentage of bone ash and phytate P disappearance compared with the groups fed dl-Met only when phytase was added to the diets. The additions of citric acid and HMB improved phytate P utilization. However, the reason why some organic acids are effective whereas others are not is not apparent.

There is considerable data on the effect of reducing inorganic Ca and P in broiler finisher diets on carcass quality. However, there is limited information on the effect of reducing dietary Ca and P during the different phases of growout. Two experiments were conducted from 0 to 35 d in floor pens. In both experiments, at least 4 replicates per treatment (50 chicks per replicate) were used. Corn-soybean meal and soybean oil-based diets deficient in Ca and P were fed. During the starter phase (ST), from 0 to 18 d, chicks were fed a 23% CP diet containing 0.60% Ca and 0.47% total P (tP). During the grower-finisher phase (GF), from 19 to 35 d, birds were fed a 19% CP diet containing 0.30% Ca and 0.37% tP. A combination of 1,000 phytase units/kg of Natuphos phytase and 5 microg/kg of 1alpha-hydroxycholecalciferol (P + 1alpha) was supplemented to some of the feed during the ST and GF. Diets containing adequate Ca and P were also fed during the ST (0.90% Ca and 0.68% tP) and GF (0.80% Ca and 0.67% tP). The level of tibia ash and the incidence of bone disease were measured at 18 and 35 d. At the end of the experiments, birds were processed and evaluated for muscle hemorrhages and broken bones. In both experiments, broilers fed diets that were not P + 1alpha supplemented demonstrated poor bone mineralization, considerable leg problems, and a high incidence of broken bones after processing. Broilers fed P + 1alpha throughout had more broken clavicles and femurs compared with birds fed the adequate diets. Day-18 tibia ash was significantly correlated to broken tibias and femurs during processing. Day-35 tibia ash was better correlated to bloody breast meat than to broken bones. It is concluded that carcass quality depends on the levels of Ca and P fed and the age of the bird. Tibia ash, traditionally used as an indication of bone strength, was better correlated to the incidence of bloody breasts.

An experiment was conducted with 25- to 66-wk-old Ross broiler breeders in an environment excluding ultraviolet light to determine the cholecalciferol (D3) requirements for hen day egg production; hatchability; body weight of the progeny at 1 d; embryo mortality during the early (1 to 10 d of incubation), middle (11 to 15 d of incubation), and late stages (16 to 21 d of incubation) of development; egg weight; specific gravity; and body ash of the progeny at 1 d of age. Five levels of vitamin D3 (125, 250, 500, 1,000, and 2,000 IU/kg of diet) were fed to hens from 25 to 66 wk of age. One additional group was fed no supplemental D3 until 36 wk of age and was then changed to 4,000 IU/kg of diet. Separate regression analyses were performed for wk 27 to 36 (peak original design) and for wk 37 to 66 (postpeak production modified design). The D3 levels for the predicted maximum hen day egg production during peak and postpeak were 1,424 and 2,804 IU/kg, respectively. The D3 levels for the predicted maximum hatchability were 1,390 IU/ kg (peak) and 2,708 IU/kg (postpeak). The level of D3 that resulted in the minimum early embryo mortality was 1,288 IU/kg at peak; however, no significant effect was observed at postpeak. The D3 levels for minimum middle stage embryo mortality were 1,130 IU/kg (peak) and 2,568 IU/kg (postpeak) and for late stage embryo mortality were 1,393 IU/kg (peak) and 2,756 IU/kg (postpeak). The D3 level for maximum egg weight was 1,182 IU/kg (peak) and for specific gravity was 1,337 IU/kg (peak) and >2,000 IU/kg (postpeak). The D3 level for maximum body ash of progeny at d 1 was >2,000 IU/kg. Analysis of the data from the original design of the experiment (treatments providing 0, 125, 250, 500, 1,000, and 2,000 IU of vitamin D3/kg for the 27- to 36-wk-old birds) indicates a requirement of approximately 1,400 IU of D3/kg of feed for broiler breeder hens. When the data from the modified experiment (37 to 66 wk of age) include conversion of the treatment provided at 0 IU of D3/kg to a treatment providing 4,000 IU of D3/kg, the requirement may be approximately 2,800 IU of D3/kg.

A study was conducted to investigate the effect of phytase on the AMEn of peanut meal. One hundred twenty Ross x Ross broiler chicks of mixed sex were fed one of 4 experimental diets from 5 to 15 d of age. Diets used were Diet 1, a low P corn-soybean based basal diet; Diet 2, a 50% basal + 50% peanut meal diet; Diet 3, the basal diet supplemented with 24,000 phytase units (FTU) of Natuphos 5000 phytase/kg; and Diet 4, a phytase-supplemented 50% basal + 50% peanut meal diet. Chromic oxide was added to the basal diet at 0.1% as an indigestible marker. Apparent metabolizable energy was determined by substituting peanut meal at the expense of the basal diet. Other parameters measured included the phytate content of the diets as well as phytate P disappearance. Phytase significantly improved phytate P disappearance for both the corn and soybean meal basal diet (23.8 to 93.7%) as well as the 50% basal + 50% peanut meal diet (16.7 to 89.5%). Phytase increased the AMEn of peanut meal on a DM basis by approximately 9%, from 3,209 to 3,559 kcal/kg.

A series of experiments was conducted to investigate the effects of maternal dietary vitamin D3 supplementation at 4 different times during the laying cycle, on the performance and bone quality of broiler chicks fed a diet that induced tibial dyschondroplasia (TD) or an adequate diet. Ross x Ross broiler breeder hens were fed a corn-soy diet with various levels of vitamin D3 from 24 to 66 wk of age. Eggs were collected at 39, 44, 53, and 64 wk of age and hatched. Chicks from hens fed 250 IU of D3/kg (low maternal D3 or LMD3) and 2,000 IU of D3/ kg (high maternal D3 or HMD3) levels were placed in battery brooders and fed the diets from 0 to 16 d. At 16 d, the chicks were weighed and killed; the left tibias were used for bone ash determinations, and the right tibias were used to score the incidence and severity of TD (0, 1, 2, or 3, where 3 is the most severe). Body weight gain and feed intake were significantly lower for the LMD3 chicks at wk 44 and 64, although there was no difference in weight at hatch. For the first 2 hatches (wk 39 and 44), the LMD3 and HMD3 chicks demonstrated high average TD scores (2.03 and 1.57 vs. 2.05 and 1.75 for the LMD3 vs. HMD3 chicks, respectively) and high average incidences of severe TD (50 and 35% vs. 45 and 34% for LMD3 vs. HMD3 levels, respectively). However, results from the last 2 hatches (wk 53 and 64) showed that HMD3 chicks, compared with LMD3 chicks, had reduced average TD scores (1.39 and 1.47 vs. 1.01 and 0.44 for LMD3 vs. HMD3 levels, respectively) and severe TD incidence (36 and 40% vs. 17 and 8% for the LMD3 vs. HMD3 levels, respectively). In this experiment, as egg production declined toward the end of the laying cycle, hens fed the HMD3 might have been able to deposit sufficient quantities of vitamin D3 in the egg to maintain excellent body weight gain at 16 d of age and reduce the incidence and severity of TD. Hens fed the LMD3 diet were unable to produce similar improvements.

Supplemental 1alpha-hydroxycholecalciferol (1alpha-OHD3) has been shown to have qualitatively similar and quantitatively additive effects to exogenous phytase. Two experiments were conducted from 0 to 35 d in floor pens to determine the additive effect of phytase and 1alpha-OHD3 when supplemented to Ca- and P-deficient diets. In both experiments, at least 4 replicates per treatment (50 chicks per replicate) were used. Corn-soybean-meal-and soybean-oil-based diets were fed and birds were raised in a house impervious to ultraviolet light. During the starter phase (ST), from 0 to 18 d, chicks were fed a 23% CP diet containing 0.60% Ca and 0.47% total P (tP). During the grower/finisher phase (GF), from 19 to 35 d, birds were fed a 19% CP diet containing 0.30% Ca and 0.37% tP. A combination of 1,000 phytase units/kg of Natuphos phytase and 5 microg/kg of 1alpha-OHD3 (P+1A) was supplemented to some of the feed during the ST and GF. Diets containing adequate Ca and P were also fed during the ST (0.90% Ca, 0.68% tP) and GF (0.80% Ca, 0.67% tP). Performance characteristics and the incidence of rickets and tibial dyschondroplasia were measured at 18 and 35 d. In experiment 1, unsupplemented chicks performed well but had considerable leg problems. Chicks fed P+1A during the ST or GF did not perform as well as birds fed P+1A throughout. Birds fed P+1A throughout performed as well birds fed the adequate diets without any indication of leg problems. In experiment 2, unsupplemented birds performed similarly to unsupplemented birds in experiment 1. However, chicks fed the supplements or the control diets did not perform as well or accumulate as much bone ash as birds in experiment 1, although the diets were formulated identically in both experiments. Diets with as little as 0.30% Ca and 0.37% tP appear to be adequate for broilers older than 18 d if supplemented with the correct amounts of phytase and 1alpha-OHD3. However, there are unknown variables that may limit the potential of broilers in terms of bone mineralization and bone pathology, even when adequate diets are fed.

Four experiments were conducted using Ross x Ross chicks hatched from broiler breeder hens fed various levels of cholecalciferol (vitamin D3; 0 to 4,000 IU/kg of diet) to determine the effect of the maternal diet on the performance and leg abnormalities of the progeny. Chicks hatched from eggs laid by the hens at different ages were used in experiments 1 to 4. The studies were conducted in an ultraviolet light-free environment as split plot designs, with Ca levels or 25-hydroxycholecalciferol (25-OHD3) in the chicks' diet as the whole plot, and vitamin D3 in the maternal diet as a subplot. Chicks in experiments 1 and 2 were fed 2 levels of Ca (0.63% or 0.90%) and chicks in experiments 3 and 4 were fed 6 levels of 25-OHD3 (0 to 40 microg/kg of diet). Significant increases in body weight gain (BWG) of the progeny were observed in experiments 1, 2, and 4 as the vitamin D3 level in the maternal diet increased. Chicks hatched from eggs laid by hens fed the highest levels of D3 had the highest tibia ash. Significant reductions in Ca rickets incidence (experiments 1 and 2) and tibial dyschondroplasia (TD) incidence (experiment 1) were observed as the level of vitamin D3 in the maternal diet increased. Chicks fed lower levels of Ca had lower BWG and tibia ash and higher incidences of TD and Ca rickets than chicks fed higher levels of Ca. Increasing the level of 25-OHD3 in the chicks' diet significantly improved BWG, tibia ash, and plasma Ca and reduced TD and Ca rickets incidence. An overall evaluation of the study indicates that chicks from hens fed the highest levels of vitamin D3 and fed high levels of Ca or 25-OHD3 had the highest BWG, tibia ash, and plasma Ca, and the lowest incidences of TD and Ca rickets.

Two experiments were conducted to examine the calcium requirements of broiler chickens fed corn-soybean meal diets. Experiment 1 used a 6 x 2 x 2 factorial arrangement and was conducted with broilers in floor pens during the grower phase (19 to 42 d). Diets were mixed with 6 levels of dietary Ca (0.325, 0.4, 0.475, 0.55, 0.625, and 0.9%) and 17 or 23% CP and fed to males and females separately. Experiment 2 was a 6 x 2 factorial design conducted using Petersime battery brooders during the starter phase (0 to 16 d). The same 6 levels of dietary Ca used in experiment 1 were fed separately to each sex, but only at the 23% level of CP. The diets used in both experiments were formulated to contain 0.45% nonphytin phosphorus. In experiment 1, grower chickens did not demonstrate significant body weight gain (BWG) or feed conversion ratio (FCR) response (g of feed per g of gain) to the different levels of Ca at either level of protein. The percentage tibia ash did not respond to increasing Ca levels beyond 0.625% Ca at either protein level. In experiment 2, BWG increased linearly up to 0.55 and 0.625% dietary Ca for males and females, respectively. Feed conversion ratio decreased linearly with increasing dietary Ca up to 0.625% Ca, and tibia ash was highest at 0.9% Ca for both sexes. These results suggest that the current NRC Ca requirements for the broiler starter (1.0%) are sufficient for maximum bone ash, but that Ca requirements for grower birds (0.9%) may be excessive for optimum BWG, FCR, and tibia ash.

Phytase supplementation over a range of different levels of dietary Ca and nonphytate phosphorus (NPP) was investigated by comparing surface response curves from regression equations generated with (experiment 1) and without (experiment 2) phytase using various performance and bone quality parameters. Cobb x Cobb broiler chicks were raised from 0 to 16 d in 2 experiments using corn-soybean meal based diets. Experiment 1 used a 4 x 4 factorial arrangement with diets formulated to contain combinations of 4 levels of Ca: 0.38, 0.58, 0.78, and 0.98% and 4 levels of NPP: 0.2, 0.3, 0.4, and 0.5%. Experiment 2 used a composite rotatable design in which rations were formulated to contain dietary Ca levels of 0.38, 0.47, 0.68, 0.89, and 0.98% and NPP levels of 0.20, 0.24, 0.35, 0.46, and 0.50%. An extra point was included in the design to contain the lowest Ca and lowest NPP levels (0.38% Ca and 0.20% NPP). All combinations of Ca and NPP were fed with 657 phytase units/kg Natuphos 5000 phytase, plus 4 combinations (0.38% Ca and 0.20% NPP, 0.47% Ca and 0.24% NPP, 0.68% Ca and 0.35% NPP, and 0.89% Ca and 0.46% NPP) were fed without phytase to determine the suitability of comparing multiple regression response surfaces for particular variables among experiments. Comparison of surfaces, with and without phytase, showed that growth and bone quality responses to phytase were greatest at low NPP levels and high Ca levels, and these decreased when the Ca level was reduced or when the NPP level was increased. A third experiment confirmed that phytase elicits a greater response at higher Ca levels and lower NPP levels (0.86% Ca and 0.20% NPP) versus low Ca levels and low NPP levels (0.47% Ca and 0.24% NPP). The data demonstrated why it is impossible to determine a single NPP equivalency value for phytase supplements.

An experiment was conducted with broiler breeder hens to determine the relative biological value of 25-hydroxycholecalciferol (25-OHD3) compared with cholecalciferol (vitamin D3) for hen-day egg production, hatchability, embryo mortality (early, 1 to 10 d of incubation, late, 11 to 21 d), and body ash of the progeny. The study was conducted with 73-to-90-wk-old molted Ross broiler breeder hens in an environment excluding ultraviolet light. A basal vitamin D3 deficient diet supplemented with 4 levels of vitamin D3 (0, 3,125, 12,500, and 50,000 ng/kg of diet) and 2 levels of 25-OHD3 (3,125 and 12,500 ng/kg of diet) was fed. The relative biological values of 25-OHD3 in comparison to vitamin D3, using slope ratio techniques, were 138, 133, 128, and 111% for hen-day egg production, hatchability, late embryo mortality, and body ash of the progeny,, respectively (average = 128%). When comparing 25-OHD3 against D3 at the 3,125 ng/kg level, the relative biological values were 209, 167, 400, and 108% for the same criteria, respectively (average = 221%). However, at the 12,500 ng/kg level no statistical differences between 25-OHD3 and D3 were observed (average = 108%). Four trials were conducted to determine the effect of the maternal diet on the performance and leg abnormalities of the hens' progeny. In experiment 1, no vitamin D was added to the corn-soybean meal basal diet fed to the chicks, and in experiments 2, 3, and 4 the basal diet was supplemented with 27.5 microg of D3/kg of diet. In the progeny study, the average relative biological value of 25-OHD3 at the 3,125 and 12,500 ng/kg levels were 115 and 101%, respectively. The potency of 25-OHD3 in relation to vitamin D3 depended on the level tested. When comparing vitamin D sources, 25-OHD3 had greater potency than D3 only at very low levels of supplementation.

Six experiments were conducted using Ross x Ross chicks hatched from eggs laid by broiler breeder hens fed various levels of vitamin D3 (0 to 4,000 IU/kg of diet) to determine the effects of vitamin D3 level in the maternal diet on the performance and leg abnormalities of their progeny. Chicks hatched from eggs laid when hens were 27, 41, 29, 36, 45, and 52 wk of age were used in experiments 1, 2, 3, 4, 5, and 6, respectively. The studies were conducted in a ultraviolet (UV)-light-free environment. Experiments 1 and 2 were conducted as complete randomized designs with the maternal diets as the treatments, and experiments 3, 4, 5, and 6 were conducted as split plot designs, with vitamin D3 in the chick diets as the whole plot and vitamin D3 in the maternal diet as a subplot. Chicks in experiments 1 and 2 were fed a vitamin D3-deficient diet, whereas chicks in experiments 3 and 4 were fed 4 levels of vitamin D3 (0 to 400 IU/kg of diet), and chicks in experiments 5 and 6 were fed 6 levels of vitamin D3 (0 to 3,200 IU/kg of D3). The highest body weight gains and tibia ash were observed in chicks hatched from hens fed the highest levels of vitamin D3 in all experiments. Reductions in the incidence of Ca rickets were observed in experiments 3 and 6, whereas increases in tibia ash were observed in experiments 2 and 6 as the level of vitamin D3 in the maternal diet increased. Body weight gain and tibia ash increased and Ca rickets incidence decreased as the vitamin D3 level in chick diets increased. An evaluation of the study indicates that chicks hatched from eggs laid by hens fed 2,000 or 4,000 IU of D3/kg as the maximum level of vitamin D3 had the highest body weight gains, and chicks fed 3,200 IU had the highest body weight and tibia ash and the lowest TD and Ca rickets incidences.

The current study was undertaken to evaluate the correlated responses to 3 generations of divergent selection for phytate phosphorus bioavailability (PBA) in the Athens-Canadian randombred chicken population. The traits studied were BW at 4 wk of age, BW gain (BWG), feed consumption (FC), and feed conversion ratio (FCR) during a period of 3 d. The first evaluation criterion was the cumulated divergent correlated response (CR(C)), which was calculated as the line difference of the least square means of phenotypic values for each trait at a given generation after adjustment for sex and hatch effects. The results showed a consistent correlated response in BW across generations. The CR(C) at generation G3 was 26.8 g (P < 0.01). The chickens in the low PBA line (L line) had higher BW than the high PBA line (H line). The CR(C) for BWG, FC, and FCR were significant (P < 0.05) only at G3. The second evaluation criterion was the average best linear unbiased prediction estimated breeding value (EBV). The results showed asymmetric genetic trends in BW, BWG, and FC, and the correlated responses were mainly due to the genetic changes that occurred in H line because little genetic change occurred in L line across generations. At G3, the line differences of EBV were close to the CR(C) values for all the traits except FCR. This suggested that CR(C) and EBV criteria would tend to be consistent with the increase across generations. However, at G1 and G2, the line differences of the EBV actually deviated from the CR(C) values for BWG and FC. The inconsistency could be attributed to experimental errors and genetic drift that were not accounted by the fixed model for obtaining CR(C).

The current study was undertaken to evaluate the direct response to 3 generations of divergent selection for phytate P bioavailability (PBA) in the Athens-Canadian randombred chicken population. Cumulated divergent response (R(C)) was measured as the line difference in PBA at a given generation after adjusting for hatch and sex effects. Results showed a significant response at generation (G)1. The R(C) was unchanged from G1 to G2 and increased (1.62%) from G2 to G3 (P < 0.01) due to the application of best linear unbiased prediction (BLUP) selection in the line selected for high PBA at G2. The average BLUP estimated breeding values were used to estimate the genetic trend for the selected trait across generations. The results showed that the genetic trend was symmetric at G1 and G2 but asymmetric at G3. The application of mixed model methodology was effective in separating the environmental component from phenotypic change. When the data of the high (H) line or the low (L) line in the selected generations (G1 to G3) were combined with the data from the base population (G0), the heritability estimates for PBA were 0.07 +/- 0.02 and 0.09 +/- 0.02, respectively. The line selected for high PBA showed gain, and the line selected for low PBA showed a decrease in estimated breeding values across the generations. The results demonstrated that modest progress could be obtained by incorporating PBA into selection programs. However, other correlated traits of economic importance need to be evaluated before any decision to incorporate selection of PBA into breeding schemes be initiated.

The current study was undertaken to establish a population from an unselected random-mating chicken population for the development of a model to predict factors that affect phytate P utilization in growing birds. A population was established from a mating of 40 male and 200 female chickens from the Athens Canadian randombred population. At 4 wk of age, birds were housed in individual metabolic cages and fed a diet containing 1.06% Ca, 0.35% total P, and 0.03% available P. After 3 d of acclimatization, feed consumption (FC) was measured and excreta produced in 3 consecutive d were collected. Individual 4-wk BW, BW gain (BWG), phytate P intake (PPI), inorganic P intake (IPI), Ca intake (CaI), N intake (NI), and energy intake (EI) during the 3 d excreta collection period were also measured. Feed conversion ratios (FCR) and relative growth rate were calculated. Phytate P bioavailability (PPB), Ca bioavailability (CaB), and N bioavailability (NB) were estimated from the disappearance of the nutrients during the passage of feed through the gastrointestinal tract. Energy bioavailability (EB) was measured by bomb calorimetry as the difference in the gross energy of the feed and the energy of the excreta. The major factors affecting PPB were CaB and EB for both sexes. In the males, BW contributed significantly to PPB. However, in the females, NB also contributed significantly to PPB. Faster growing birds tended to have a reduced retention time of feed compared with slow growing birds, and as a result utilized phytate P less. Birds that are able to utilize phytate P better are putatively able to release P for energy utilization. Therefore, the birds that were able to utilize phytate P better were also better energy utilizers.

An experiment was conducted to determine the effects of soybean meal (SBM) particle size on broiler performance, particularly P utilization. This experiment utilized a 2 x 2 x 2 factorial design with the following variables: SBM particle size, P level, and diet type, either corn-SBM or semipurified. SBM was obtained from a processing plant before (geometric mean diameter 1,239 microm) and after (891 microm) hammer milling. The P levels were 0.5% total P for deficient diets and 0.7% total P for adequate P diets. The coarse SBM improved bone ash (P < 0.05), gain:feed ratios (P < 0.1), and plasma P levels (P < 0.1). The diets with 0.5% P resulted in overall poorer performance as 16-d BW was reduced, gain:feed ratio decreased, bone ash decreased, and rickets incidence increased. Chicks fed the semipurified diets also had lower 16-d BW, lower gain-to-feed ratio, and lower bone ash. There was a significant interaction between the diet type and the soy particle size when the corn-SBM meal diets were fed because the coarse SBM increased plasma P levels, whereas there was little effect when the semipurified diets were fed. There were also significant interactions observed between these variables on growth and gain:feed ratio in that the coarse SBM elicited a much more dramatic response when incorporated into the semipurified diets as opposed to the corn-SBM diets. The results suggest that large particle size soybean meal may be more efficiently utilized than fine particle size soybean meal.

Six experiments were conducted to study the effects of exposure of young chickens to u.v. radiation. Chickens were fed a cholecalciferol (D3)-deficient diet and exposed to u.v. radiation from fluorescent lights giving total radiance (285-365 nm) at 0.15 m of 99.9 mJ/s per m(2). In Expt 1, chickens had increased body weight, bone ash and plasma Ca and decreased incidence of rickets and tibial dyschondroplasia (TD) when exposed to fluorescent light radiation 24 h per d, 24 h every 2 d, or 24 h every 3 d starting with exposure on day 1 after hatching. However, when not exposed on day 1, but on days 4, 7, 10, 13 and 16, the bone ash was reduced, and the incidence of TD and rickets was increased, compared with chickens exposed on day 1 after hatching. When chickens were exposed at 1 d of age to radiation from two lamps, each of which gave a radiance (285-365 nm) at 0.26 m of 856 mJ/s per m(2), both the length of time of radiation and location of the lamps (above or below the chicken) influenced the response as measured by body weight, bone ash, plasma Ca and incidence of rickets. When chickens that received a TD-inducing diet were exposed to 30 min u.v. radiation from below at 1 d of age they developed significantly less TD than did those not exposed when fed either 27.5 or 55.0 microg D3/kg diet.

The current study was undertaken to estimate variance components for phytate P bioavailability (PBA) and the genetic correlations among PBA with growth and feed utilization (or intake) traits in an unselected random mating chicken population. Pedigreed data from 901 Athens-Canadian randombred chickens hatched from 26 sires, 71 dams, and 105 grandparents were used for estimation of genetic parameters. Birds were individually housed in metabolic cages at 4 wk of age and fed a 0.35% P diet. After 3 d of acclimatization, excreta produced for 3 consecutive d were collected and feed consumed (FC) was measured. Individual 4-wk BW and BW gain (BWG) during the 3-d excreta collection period were also measured. Feed conversion ratios (FCR) were calculated. Phytate P bioavailability was estimated from the disappearance of phytate during the passage of feed through the gastrointestinal tract. The restricted maximum likelihood method with the average information matrix algorithm was used for the estimation of variance components. The heritability estimate for PBA was about 0.10. Genetic correlations between PBA and BW, BWG, and FC were moderate and negative, indicating that improving PBA utilization would moderately affect growth. The genetic correlation between PBA and FCR was negligible and suggested that selection for PBA will not adversely affect FCR. The economic implications of genetically modifying poultry to improving phytate P utilization and the subsequent elimination or reduction of the amount of phytase used in poultry diets are yet to be determined.

This study evaluated the overall performance of 0-to-16-d-old, mixed-sex, Cobb x Cobb broiler chicks when dietary phytase levels were supplemented in excess of industry standards. The experimental diet used consisted of a basal corn-soybean meal diet that contained an analyzed 22.2% CP, 0.88% Ca, a deficient total P (tP) level of 0.46% (phytate P = 0.272%), and calculated ME of 3.123 kcal/g diet on an as-is basis. In addition to a positive control diet [0.70% tP], the dietary phytase levels evaluated were 0, 93.75, 187.5, 350, 750, 1,500, 3,000, 6,000, and 12,000 U/kg of diet. Supplementing phytase from 0 to 12,000 U significantly increased body weight gain from 287 to 515 g/chick, feed intake from 381 to 595 g/chick, gain to feed from 0.755 to 0.866, plasma P from 2.5 to 7.1 mg/100 mL, tibia ash from 26 to 41%, tibia ash weight from 0.200 to 0.601 g/tibia, tP retention from 51 to 80%, phytate P disappearance from 40% to 95%, apparent N retention from 58 to 78%, AMEn from 3,216 to 3,415 kcal/kg diet, and reduced P rickets from 80 to 3%. Using nonlinear regression analysis on log-transformed phytase levels, gain to feed, apparent N retention, and AME, responded linearly with respective R2 values of 0.76, 0.82, and 0.72, whereas body weight gain, feed intake, plasma P, P rickets, tP retention, phytate P disappearance, tibia ash percentage, and tibia ash weight responded quadratically with respective R2 values of 0.93, 0.88, 0.85, 0.84, 0.91, 0.96, 0.96, and 0.98. Few statistical differences existed between response data for broilers consuming the positive control diet or diets containing 1,500 to 12,000 U of phytase (P > 0.05). This finding indicates that broilers consuming a tP-deficient corn-soybean meal diet can achieve maximum performance when phytase is supplemented to 12,000 U/kg diet and that current phytase supplementation levels within the poultry industry may need to be reevaluated.

An experiment was conducted to compare two common methods of estimating bone ash from growing broiler chicks (A = autoclaving; B = boiling/extracting). Ross x Ross 1-d-old broiler chicks were fed a corn-soy, phosphorus-deficient diet (22.7% CP, 1% calcium, 0.22% non-phytate phosphorus), with 0, 750, 1,500, 3,000, or 6,000 units of phytase (FTU) to produce bones with a range of ash. The methods were compared with bones from chicks at 7, 14, and 21 d of age. Left legs were used for method B, and right legs were used for method A. Data was analyzed by the general linear models procedure of SAS software, and differences between means were detected using the Duncan's new multiple range test at the 0.05 level. Variance estimates were the mean square errors (from SAS outputs). Sample sizes needed to detect a 2% difference in bone ash were calculated using the method of Zar. The addition of 6,000 FTU/kg increased tibia ash from 26 to 37%, 29 to 41%, and 33 to 43% on Days 7, 14 and 21, respectively (method B). With bones from 7-d-old chicks, the same number of samples was necessary to detect a 2% difference using methods A and B. With bones from 14- and 21-d-old chicks, approximately 50 and 150% more samples were necessary, respectively, using method A. The autoclaving method is less labor-intensive and requires no toxic solvents, but for older birds, many more samples or replications are needed to detect the same treatment differences.

Studies were conducted to determine the effect of dietary supplementation with cholecalciferol (D3), 1,25-dihydroxycholecalciferol [1,25-(OH)2D3], 1alpha-hydroxycholecalciferol (1alpha-OHD3), and 25-hydroxycholecalciferol (25-OHD3) on utilization of phytate P by broiler chickens. Three experiments were conducted with corn-soybean meal type diets with D3 and 1,25-(OH)2D3 being tested in one experiment and 1,25-(OH)2D3, 1alpha-OHD3, and 25-OHD3 being tested in two experiments of exactly the same design. In the first experiment, high levels of D3 (110 microg and 220 microg/kg of diet) increased phytate P utilization, but the increase was not as great as that obtained from 1,25-(OH)2D3 supplementation. In the other two experiments, 1,25-(OH)2D3, D3 and 1alpha-OHD3 were consistently effective in increasing phytate P utilization as measured by plasma Ca and P, incidence of P rickets, bone ash, and retention of Ca, P, and phytate P. Supplementation with 25-OHD3 in general gave smaller and more inconsistent responses to these criteria, indicating some inconsistency in its ability to improve phytate P utilization.

Two experiments were conducted using a corn-soybean meal diet that meets or exceeds the NRC (1984) requirements for all nutrients except cholecalciferol (D3) to determine the effectiveness of 1-alpha-hydroxycholecalciferol (1alpha-OHD3) as a substitute for D3 in the diet of young broilers. Ross x Ross mixed-sex, 1-d-old chicks were reared in Petersime battery brooders not exposed to ultraviolet light with feed and water supplied ad libitum for 16 d. In Experiment 1, D3 was fed at 0, 2.5, 5, 10, 20, and 40 microg/kg and one source of 1alpha-OHD3-(Hoffmann-LaRoche, Inc.; HLR) was fed at 0.625, 1.25, 2.5, 5, and 10 microg/kg of diet. In Experiment 2, the D3 was fed at 0, 2.5, 5, and 10 microg and two sources of 1alpha-OHD3-[HLR and Majestic Research Inc. (MRI)] were fed at 0, 0.625, 1.25, and 5 microg/kg of diet. Slope ratio analysis of data from the measurement of 16-d body weight, plasma Ca, rickets, and bone ash indicated bioavailability of the 1alpha-OHD3 as compared to D3 from 1.88 to 21.2. Percentage bone ash gave the most precise values in both experiments. Considering all the data from both experiments, the 1alpha-OHD3 appears to be approximately eight times as effective as D3 for satisfying the requirements of several criteria in two experiments with broiler chickens.

Two experiments were conducted with broiler chicks in battery brooders from 1 to 18 d of age to determine Trp requirements and to evaluate the performance of different genotypes (classic vs. high yield and male vs. female). Experiment 1 was a 6 x 2 factorial experiment, with six levels of Trp (0.09, 0.12, 0.15, 0.18, 0.21, and 0.24% of the diet) and two broiler chicken strains (male Arbor Acres Classic and Arbor Acres High Yield). Experiment 2 was a 6 x 2 factorial design with the same levels of Trp as in Experiment 1 and two sexes (males and females); Ross x Ross 308 birds were used. Both experiments had four replicate pens of eight birds each per treatment. The basal diet was based on corn (70.79%), corn gluten meal (17.44%), and gelatin by-product and poultry fat (23% of CP and 3.34 kcal/g of ME). At 18 d of age, three birds per replicate were killed, and livers and fat pads were removed. The broken-line linear model was used to estimate the chicks Trp requirement. Liver or liver fat and fat pad weights (as a percentage of body weight) were affected by dietary Trp level. In Experiment 1, the Trp requirements differed little; for gain they were 0.18 +/- 0.002% and 0.17 +/- 0.002%, and for feed conversion they were 0.16 +/- 0.004% and 0.16 +/- 0.002%, for the Classic and High Yield broilers, respectively. In Experiment 2, the Trp requirement of males was 0.17 +/- 0.003% for BW and 0.17 +/- 0.003% for feed conversion, and that of females was 0.17 +/- 0.003% for body weight and 0.16 +/- 0.001% for feed conversion. There was no apparent difference in the Trp requirement of young broilers due to genetic stock or gender (P > 0.05).

The objectives of this work were to study the responses of one Leghorn and two broiler stocks and sexes to different levels of Thr and to estimate their requirements for this amino acid. All experiments were conducted with birds from 1 to 18 d of age. Body weight gain (BWG) and feed consumption were measured on the eighteenth day, and feed conversion ratio (FCR) was calculated. At Day 18, three birds per replicate were killed, and liver and fat pads were collected and weighed. The data were analyzed by the general linear model and nonlinear model procedures of SAS software, and the broken-line linear model was used to estimate Thr requirements of chicks. Experiment 1 had a 5 x 3 factorial design with five levels of Thr (0.63, 0.70, 0.77, 0.84, and 0.91% of the diet), two broiler genotypes (Arbor Acres Classic and High Yield), and one Leghorn genotype (Hy-line W-36), with three replicate pens of eight male birds each. The basal diet was composed of corn, peanut meal (PNM), poultry by-product meal, poultry fat, DL-Met, L-Lys, and L-Ile (23% CP and 3.2 kcal/g of ME). The Leghorn chicks did not respond to Thr supplementation, indicating their requirement was < or = 0.63%. High Yield birds had better BWG and FCR than Classic. The BWG and FCR were reduced more in Classic than High Yield strains by the lowest Thr level. The percentage of liver was higher in the Classic than High Yield strain broilers with Thr supplementation. The second experiment (2 x 2 x 2 factorial design) was conducted to evaluate the effects of two levels of Thr (0.63 and 0.90%), two levels of Ile (0.72 and 0.90%), and two broiler strains (as Experiment 1). There were no responses to Ile for any parameters measured. Experiment 3 (6 x 2 factorial design, corn, PNM-based basal diet) had six Thr levels (0.63, 0.67, 0.71, 0.75, 0.79, and 0.83%) and two broiler strains (as Experiment 1), with four replicate pens of eight male birds each. The High Yield strain broilers grew significantly better at the lowest Thr level, but performance was similar at the higher Thr levels (significant interaction, P = 0.018). FCR was affected by Thr level but not by strain. The Thr requirement of the Classic strain broilers was 0.69 +/- 0.01% for BWG and 0.68 +/- 0.01% for FCR. The Thr requirement of the High Yield strain broilers was 0.68 +/- 0.01% for BWG and 0.69 +/- 0.01% for FCR. The Thr requirements of male versus female High Yield strain broilers were evaluated in a 6 x 2 factorial design, with six Thr levels (Experiment 4), with four replicate pens of eight birds each. Males and females had the same performance and carcass composition results (P > 0.05), except for percentage abdominal fat pads. The Thr requirement was 0.71 +/- 0.01% for BWG and 0.71 +/- 0.01% for FCR for the males and 0.72 +/- 0.008% for BWG and 0.71 +/- 0.001% for FCR for females. Excellent performance was observed from the corn- and PNM-based diet supplemented to contain 0.72% Thr. The Thr requirements of High Yield and Classic broilers (males and females) were similar and greater than for the Leghorn strain studied.

1. The effects of maize particle size and steam pelleting on growth and nutrient utilisation were studied with broiler chicks. 2. The presence or absence of 10 microg/kg of 1,25 dihydroxycholecalciferol in diets adequate or deficient in phosphorus was also investigated. Food efficiency was superior with the fine maize diets but calcium retention and phytate phosphorus retention were greatest with the coarse maize diets. Pelleting improved food efficiency and growth in both experiments while phytate phosphorus utilisation was decreased. 3. Addition of 1,25-dihydroxycholecalciferol to the diet increased 16-d body weight, bone ash, plasma dialysable phosphorus and retentions of total phosphorus and phytate phosphorus while decreasing phosphorus deficiency rickets and tibial dyschondroplasia. 4. There were significant interactions between maize particle size and food form. The improvement in calcium retention observed with the coarse maize diets was reduced when the diets were pelleted. When fed as a mash, coarse maize diets resulted in increased plasma dialysable phosphorus levels but when the diet was pelleted this response was eliminated. 5. There was also a significant interaction between particle size and phosphorus concentration in that chicks given diets deficient in phosphorus had improved bone ash when fed coarse maize as compared to fine maize. However, this response was eliminated when the diets were adequate in phosphorus. 6. In one experiment, fine maize diets had higher metabolisable energy values and there was a significant interaction between maize particle size and food form as pelleting improved the metabolisable energy value of coarse maize diets but not fine maize diets. In another experiment only pelleting of the factors studied improved the metabolisable energy value of the diets.

One hundred forty-three broiler chick excreta samples were obtained from previous experiments dealing with phytate phosphorus utilization. The air-dried samples were ground in a Cyclotech 1093 sample mill and analyzed for the following: moisture, N, Ca, energy, total P, and phytate P. By chemical assay, the sample compositions were moisture: mean = 9.62, SD = 1.27% (range = 7.37-13.59); N: mean = 5.31, SD = 0.37% (range = 4.28 to 6.48); Ca: mean = 1.66, SD = 0.32% (range = 0.85 to 2.6); total P: mean = 1.13, SD = 0.28% (range = 0.66 to 1.75); gross energy: mean = 3,560, SD = 120 kcal/kg (range = 3,309 to 3,882); phytate P: mean = 0.63, SD = 0.17% (range = 0.32 to 0.97). The samples were scanned in a Feed & Forage Analyzer Model 5000 with near-infrared reflectance spectroscopy (NIRS)-2 Software. One hundred twenty-three samples were used to create the calibration curves (20 randomly selected samples were set aside for validating the calibration). The combination of math treatments and scatter corrections that provided the best standard error of cross validation (and its correlation coefficient) was chosen for the standard curves. The coefficients of determination (R2) were moisture, 0.96; N, 0.88; Ca, 0.84; total P, 0.91; gross energy, 0.86; and phytate P, 0.86. The standard errors of prediction were moisture, 0.342%; N, 0.193%; Ca, 0.143%; total P, 0.134%; gross energy, 74.66 kcal; and phytate P, 0.91%. We concluded that it is possible to predict the moisture, N, Ca, gross energy, total P, and phytate P in broiler excreta by using NIRS.

Three experiments were conducted to test the potencies of nine sources of cholecalciferol using a chick bioassay. The tested products were compared with a Sigma Reference Standard (SRS). All of the diets fed to the chicks were prepared from corn-soybean meal. Each of the products was in premix form containing cholecalciferol. Their physical characteristics reflected the methods used to produce the premixes. They were categorized as spray-dried or drum-dried in the beadlet or flake form. Basal diets without cholecalciferol were used in all experiments. For Experiments 1 and 2, the designs were a 2 x 3 factorial arrangement using three different cholecalciferol products and two levels of 200 and 400 IU/kg dietary cholecalciferol. For both experiments, three additional SRS levels of 600, 800, and 1,000 IU/kg were included in the studies as positive controls as there is a possibility that the cholecalciferol products being tested may exhibit activity higher than the amount stated. In Experiment 3, a 3 x 4 factorial arrangement was used, which was represented by three cholecalciferol products and four levels of dietary cholecalciferol at 150, 300, 600, and 1,200 IU/kg. By using the slope ratio analysis, the potencies of the products from the three experiments were between 86 and 118%. In Experiment 3, the requirement of chicks for cholecalciferol using the three tested products, as determined by a nonlinear regression model based on bone ash, were 843+/-85, 911+/-106, and 986+/-131 IU/kg of diet as compared with 915+/-82 IU/kg when using the SRS. The results from these studies indicate that the chemical assays used to determine the cholecalciferol activity of these products were very reliable.

Several excellent reviews regarding nutrition and skeletal disorders have appeared in the last 20 yr. This review will cover several areas of vitamin D research, the area of feed deprivation, and bone abnormalities, because there has been considerable interest in these areas during the past 10 yr. Studies indicate that the quantitative requirement for cholecalciferol (D3) for broiler chickens is much greater than previously thought. Ascorbic acid may play a role in stimulating 1-hydroxylation of 25-hydroxycholecalciferol [25-(OH)D3], but the evidence is not clear under exactly what conditions this relationship is important in practical prevention of tibial dyschondroplasia. Studies indicate that dietary supplementation with 1,25-dihydroxycholecalciferol [1,25(OH)2D3] will reduce the incidence of tibial dyschondroplasia in three different strains of broilers bred to develop a high incidence of the disease. But it did not prevent the disease totally in the strains, unless high enough levels of 1,25-(OH)2D3 were fed to reduce growth rate. These studies indicate that these high tibial dyschondroplasia strains have a defect(s) in vitamin D metabolism. Studies continue to elucidate the role of ultraviolet light in preventing leg abnormalities. Only a few studies have been conducted on the efficacy of various vitamin D3 derivatives to prevent tibial dyschondroplasia. Feed deprivation continues to be an intriguing method of preventing tibial dyschondroplasia, and examination of exactly how this prevents the bone abnormality could open avenues for explaining the disease.

Three experiments were conducted to determine the effects of pelleting and extrusion of feeds on the utilization of phytate P by broilers. The first experiment investigated the effects of pelleting the whole corn-soybean meal (SBM) diet, the corn, or SBM separately on phytate P utilization. The P-deficient basal diet contained 0.5% total P and 0.2% phytate P. Steam pelleting the whole diet, the corn, or SBM separately did not decrease the severity of the P deficiency obtained and there were no indications of increased phytate P utilization. In the second experiment, the whole corn-SBM P-deficient diet was extruded. Extrusion of the diet did not influence bone ash and P rickets, both sensitive criteria of P deficiency. Extrusion decreased Ca, P, and phytate P retention and decreased the ME value of the diet. In the third experiment, phytate P retention by chickens fed three commercial pelleted diets was compared to chicks fed the corn-SBM P-deficient diet. Phytate P retention by the chickens fed the commercial diets was much lower than retention by chickens fed the corn-SBM P-deficient diet. These studies gave no indication that pelleting or extrusion of corn-SBM diets would increase phytate P utilization by broiler chickens.

Two experiments were conducted to investigate the effects of supplementing a corn-soybean layer diet with either phytase, 1,25-dihydroxycholecalciferol [1,25-(OH)2D3], or their combination. The basal diet was formulated to contain 3.00% Ca and 0.33% total P. In Experiment 1, 160, 56-wk-old laying hens were randomly assigned to treatment groups fed either the basal diet alone or diets supplemented with either 600 phytase units (FTU) per kilogram feed, 5 microg 1,25-(OH)2D3/kg feed, or their combination for an experimental period of 9 wk. Experiment 2 had the same design and treatment groups except that laying hens 24 wk of age were used for 8 wk. In both experiments, phytase had a positive effect on BW and increased plasma dialyzable P, tibia bone ash, and phytate P retention. In the first experiment, the addition of phytase, 1,25-(OH)2D3, or their combination prevented a rapid decrease in egg production due to a Mycoplasma gallisepticum infection observed in hens fed the basal diet. However, no benefit in egg production was obtained in the second experiment. No effects on egg weight and egg specific gravity were observed in both experiments. These results clearly indicate that phytase, and to a lesser extent 1,25-(OH)2D3, can be used to increase the utilization of phytate P by laying hens.

Three experiments were conducted to determine the influence of vitamin A on the utilization and amelioration of toxicity of cholecalciferol (vitamin D3), 25-hydroxycholecalciferol [25-(OH)D3], and 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] in young broiler chicks. Two levels of vitamin A (1,500 and 45,000 IU/kg or 450 and 13,500 microg) were fed in all experiments. In Experiment 1, chicks were fed six levels of vitamin D3 (0, 5, 10, 20, 40, and 80 microg/kg). High dietary vitamin A decreased bone ash (P < 0.001), and increased the incidence of rickets (P < or = 0.02). Linear and quadratic responses to vitamin D3 levels were significant (P < 0.01) for body weight, bone ash, incidence and severity of rickets, and plasma calcium. In Experiment 2, six levels of 25-(OH)D3 (0, 5, 10, 20, 40, and 80 microg/kg) were added to the basal diet. Adding 25-(OH)D3 increased (P < 0.001) body weight, bone ash, and plasma calcium, and decreased rickets and plasma vitamin A. Adding 25-(OH)D3 overcame the reduction in bone ash produced by high dietary vitamin A showing a significant (P < 0.02) interaction. In Experiment 3, six levels of 1,25-(OH)2D3 (0, 2, 4, 8, 16, and 32 microg/kg) were added to the basal diet. High dietary vitamin A increased (P < 0.01) the incidence and severity of rickets. Adding 1,25-(OH)2D3 increased (P < 0.01) body weight, bone ash, plasma calcium, and reduced rickets and plasma and liver vitamin A. Adding 1,25-(OH)2D3 overcame the reduction in bone ash, and the increase in rickets produced by high vitamin A was significant (P < or = 0.05). These results indicate that high dietary vitamin A (45,000 IU/kg) interferes with the utilization of vitamin D3, 25-(OH)D3 and 1,25-(OH)2D3, increasing the requirement for each of them. Moreover, 45,000 IU/kg of dietary vitamin A ameliorated the potential toxic effects of feeding high levels of vitamin D3, 25-(OH)D3 and 1,25-(OH)2D3 to young broiler chickens. Further work is necessary to find the minimum levels of these vitamins needed to cause these effects.

Experiments were conducted to determine whether dietary 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] will alleviate a cholecalciferol deficiency induced by low dietary cholecalciferol and no fluorescent lighting and to determine cholecalciferol requirements as influenced by fluorescent lighting or 1,25-(OH)2D3. In each study, nutritionally complete basal diets were fed to broiler cockerels from 1 to 16 d of age. Experiment 1 had a 2 x 2 x 2 factorial arrangement of treatments with 1,25-(OH)2D3 at 0 and 10 micrograms/kg, cholecalciferol at 2.75 and 27.5 micrograms/kg, and fluorescent lights on or off. Experiments 2 to 4 had four levels of dietary cholecalciferol (0, 5.0, 27.5, and 50.0 micrograms/kg) and fluorescent lights on or off (Experiment 2) or 1,25-(OH)2D3 at 0 and 10 micrograms/kg (Experiments 3 and 4). In Experiment 1, fluorescent lighting increased bone ash, and decreased the incidence and severity of rickets at 2.75 micrograms/kg cholecalciferol and 0 microgram/kg 1,25-(OH)2D3 and reduced the severity of TD at both levels of cholecalciferol and 0 microgram/kg 1,25-(OH)2D3. In all cases 1,25-(OH)2D3 improved bone ash. The metabolite also decreased the incidence and severity of TD at both cholecalciferol levels with lights off and decreased the incidence and severity of rickets at 2.75 micrograms/kg cholecalciferol and lights off. In the absence of fluorescent lighting and 1,25-(OH)2D3 27.5 micrograms/kg cholecalciferol reduced the incidence and severity of rickets to levels equivalent to those produced by either fluorescent lighting or 1,25-(OH)2D3 alone (Experiments 2, 3, and 4). However, even 50.0 micrograms/kg cholecalciferol was not as effective as fluorescent lights or 1,25-(OH)2D3 in reducing the incidence and severity of TD.

Three experiments were conducted to examine the efficacy of dietary 1,25-dihydroxycholecalciferol [(1,25-(OH)2D3)] on the development of tibial dyschondroplasia (TD) in chickens divergently selected for high (HTD) and low (LTD) incidences of TD. In Experiment 1, chickens from the two lines were fed two calcium levels (0.75 and 1.0%), with and without 5 micrograms/ kg dietary 1,25-(OH)2D3. In Experiment 2, both lines were fed diets containing 1.0% calcium and 0, 5, 10, or 15 micrograms/kg 1,25-(OH)2D3. The addition of 1,25-(OH)2D3 did not reduce the overall incidence of TD in Experiment 1, but did reduce the incidence of severe TD from 69 to 48% in the chickens receiving the 0.75% calcium diet. In this experiment, LTD chickens had higher plasma phosphorus and bone ash. No line differences were noted between plasma vitamin D metabolites or intestinal vitamin D receptors. In Experiment 2, 5 micrograms/kg of 1,25-(OH)2D3 decreased the incidence of TD from 94 to 76% and number three scores from 69 to 44% (P < or = 0.001). Higher amounts of 1,25-(OH)2D3 further decreased TD, but there was a reduction in body weight above 5 micrograms/kg. Plasma 25-hydroxycholecalciferol [25-(OH)D3] and 1,25-(OH)2D3 were higher and intestinal vitamin D receptors were lower in HTD chickens than in LTD chickens. Plasma 1,25-(OH)2D3 was not affected by dietary treatment, but 25-(OH)D3 was reduced by dietary 1,25-(OH)2D3. Experiment 3 was conducted to examine effects of line and dietary 1,25-(OH)2D3 on plasma vitamin D metabolites and intestinal and growth plate receptors. No effect of genetic line or dietary 1,25-(OH)2D3 was observed for vitamin D receptors concentration or plasma 1,25-(OH)2D3 levels. Plasma 25-(OH)D3 was reduced when 1,25-(OH)2D3 was fed. These results indicate that HTD chickens are somewhat responsive to dietary 1,25-(OH)2D3, but this treatment failed to prevent the lesion in a large portion of the population.

Four experiments were conducted to investigate the effects of ultraviolet (UV) light exposure and several cholecalciferol metabolites on the development of tibial dyschondroplasia (TD) and other parameters associated with vitamin D metabolism in chickens selected for high (HTD) and low (LTD) incidence of TD. In Experiment 1, exposure of chickens to UV light reduced the incidence and severity of TD more in LTD chickens than in HTD chickens, as evident by the significant interactions (P < 0.10 and 0.04). In Experiment 2, the addition of cholecalciferol to diets that were deficient in cholecalciferol linearly decreased the incidence of vitamin D rickets and increased bone ash, but increased the incidence of severe TD. The LTD chickens had a higher maximal bone ash of 40.0 +/- 0.7% than did the HTD chickens, which had a maximal bone ash of 37.0 +/- 0.7%. In Experiment 3, the addition of 5 micrograms/kg of 25-hydroxycholecalciferol [25-(OH)D3], 1-alpha-hydroxycholecalciferol, or 1,25- dihydroxycholecalciferol decreased the incidence and severity of TD in the LTD chickens and had no effect on TD in HTD chickens. In Experiment 4, increasing dietary 25-(OH)D3 increased plasma 25-(OH)D3 levels in both lines, but HTD chickens had higher plasma 25-(OH)D3 levels at 20 and 40 micrograms/kg of dietary 25-(OH)D3. The incidence and severity of TD were reduced in the LTD chickens by dietary 25-(OH)D3, but little effect was noted in HTD chickens. The LTD chickens reached a maximal bone ash at 9.7 +/- 1.9 micrograms/kg and HTD chickens reached the same bone ash at 33.0 +/- 7.0 micrograms/kg. These results indicate that UV light and vitamin D metabolites are not effective in preventing TD in HTD chickens, but that altered vitamin D metabolism does exist between HTD and LTD chickens.

Three experiments were conducted to determine the effects of supplementing 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] and a commercial phytase product on Ca and P requirements of 0- to 21-d-old broiler males. These experiments were conducted with four levels of dietary Ca and P in corn-soybean diets with and without supplementation of 5 micrograms/kg of 1,25-(OH)2D3, 600 units/kg of phytase, and the combination of these supplements. The results show that these levels of phytase and 1,25-(OH)2D3 can replace up to 0.1% of the inorganic P for criteria such as BW, bone ash, and plasma P. Both supplements increased phytate P retention, whereas higher levels of Ca and P decreased phytate P retention. The addition of 1,25-(OH)2D3, but not phytase, reduced Ca requirements and decreased the incidence of tibial dyschondroplasia. The combination of these levels of phytase and 1,25-(OH)2D3 replaced 0.2% inorganic P for criteria such as BW, bone ash, and P rickets. Total dietary P requirements are estimated to be between 0.55 and 0.60% at the levels of phytase and 1,25-(OH)2D3, listed above, or 0.45% when the combination is added. The Ca requirements are estimated to be 0.77% when 1,25-(OH)2D3 is added to the diet and 0.9 to 0.95% when phytase is added.

Two experiments were conducted to compare the effects of supplementation with 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] and a commercial phytase on P utilization by broiler males. Experiment 1 was conducted with three levels of total dietary P (0.45,0.55, and 0.65%) in corn-soybean meal diets supplemented with 5 micrograms/kg of 1,25-(OH)2D3, 600 units/kg of phytase, or the combination of these supplements in a factorial arrangement from 0 to 21 d in battery brooders. A second experiment was conducted with a similar design except that it was carried out in floor pens for a period of 35 d. In Experiment 1, maximal BW was obtained at 0.65% P in chicks receiving the basal diet, 0.55% P in chicks receiving phytase or 1,25-(OH)2D3, and 0.45% P in chicks fed both supplements. Bone ash for chicks receiving the basal, phytase, 1,25-(OH)2D3, and combination treatments at 0.45% total dietary P were 26.6, 34.9, 35.1, and 38.8%. There were significant interactions between phytase and 1,25-(OH)2D3 for BW, bone ash, and incidence of rickets. Similar results were noticed in Experiment 2, with the exception that 1,25-(OH)2D3 had little influence on BW from 0 to 3 wk, likely due to slightly higher dietary P. From 3 to 5 wk, BW and bone ash were increased by each supplement and further increased by their combination. These interactions suggest different mechanisms of action for these supplements in influencing phytate P utilization.

Studies were conducted to evaluate the level of dietary 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] required to decrease the incidence of tibial dyschondroplasia (TD) in male broilers at 3 and 5 wk of age. The birds were reared in floor pens with wood shavings and fed a corn-soybean meal diet supplemented with 0, 3, 6, or 9 micrograms/kg 1,25-(OH)2D3. The diet contained, by averaged analyses, 0.73% calcium, 0.74% total phosphorus, and 0.22% phytate phosphorus. There was no treatment effect on body weight or gain: feed at either age. The incidence and severity of TD and the percentage of severe lesions were decreased and bone ash was increased by 6 micrograms/kg 1,25-(OH)2D3 at 3 wk of age. At 5 wk of age, the incidences of TD and severe lesions were decreased when 6 micrograms/kg 1,25-(OH)2D3 was fed. Bone ash was increased by this level in one of the two experiments. Plasma calcium was increased at 5 wk when 9 micrograms/kg 1,25-(OH)2D3 was fed, but there was no treatment effect on plasma dialyzable phosphorus or 1,25-(OH)2D3. The results indicate that 6 micrograms/kg 1,25-(OH)2D3 is effective for decreasing TD under practical rearing conditions.

Two experiments were conducted to determine the effects of dietary supplemental folic acid and methionine on the performance of starting broiler chicks for 18 d. Four levels of dietary folic acid (.24, .54, 1.14, and 2.34 mg/kg) and four levels of dietary methionine (.45, .53, .61, and .69%) were fed in a factorial design. There were three replicates of eight chicks each per each treatment. The basal diet was based on corn, isolated soybean protein, meat and bone meal, and fish meal. It contained adequate amounts of all nutrients except methionine and folic acid. Increased growth was observed in chicks fed the basal diet supplemented with either folic acid or methionine. Total dietary folic acid and methionine plus cysteine requirements for maximum growth were estimated to be 1.80 mg/kg and .85% in Experiment 1 and 1.47 mg/kg and .87% in Experiment 2, respectively. There were interactions between dietary folic acid and methionine on weight gain in both experiments. Chicks fed the diet containing 2.34 mg folic acid/kg tended to have depressed growth, as in previous experiments. There was a significant linear feed conversion response to folic acid in Experiment 1 and to methionine in Experiment 2. There were both linear and quadratic liver folic acid responses to dietary folic acid in both experiments. There was no indication that dietary methionine had any effect on liver folic acid content. No differences in bone ash, hemoglobin, hematocrit, or incidence of tibial dyschondroplasia were detected due to methionine or folic acid supplementation.

Two experiments were conducted to determine whether dietary 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] can prevent tibial dyschondroplasia in broiler chickens throughout the growing period when withdrawn from the grower diet. The birds were reared in floor pens with pine shavings to 6 wk in Experiment 1 and 5 wk of age in Experiment 2. Calcium was fed at .65 or 1.00% and 1,25-(OH)2D3 was fed at 0 or 5 micrograms/kg to 3 wk of age. Half the birds consuming 1,25-(OH)2D3 were then fed 0 microgram/kg until the end of the experiments. The higher level of calcium decreased the incidences of tibial dyschondroplasia and severe lesions and increased bone ash. Dietary 1,25-(OH)2D3 increased bone ash at both levels of calcium at 3 wk and the end of the experiments when supplemented for the duration of the studies. When 1,25-(OH)2D3 was fed, tibial dyschondroplasia was reduced in Experiment 2 only at 3 wk. Tibial dyschondroplasia was decreased at 5 wk in Experiment 2 when .65% calcium was fed with or without 1,25-(OH)2D3 from 3 to 5 wk of age. There were no treatment effects on plasma calcium, dialyzable phosphorus, or 25-hydroxycholecalciferol. Plasma 1,25-(OH)2D3 was decreased at 3 and 5 wk in Experiment 2 when 1.00% calcium was fed. The results of Experiment 2 suggest that 1,25-(OH)2D3 can prevent tibial dyschondroplasia caused by inadequate calcium when fed for only 3 wk. The bone ash observed when 1.00% dietary calcium is fed is equal to that obtained when 5 micrograms/kg 1,25-(OH)2D3 is fed with .65% calcium for the entire growout period.

Studies were conducted with corn-soybean meal diets to evaluate the effects of phytate phosphorus utilization on zinc absorption and retention in broiler chicks. In the first two experiments, zinc-65 was used to determine zinc absorption. Experiment 1 was a 2 x 2 factorial with 0 or 5 micrograms/kg dihydroxycholecalciferol and 0 or 40 ppm supplemental zinc. In Experiment 2, 5 micrograms/kg 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] or 750 units/kg phytase or both were added to a diet containing 35 ppm zinc. The diets in Experiment 3 were similar to Experiment 2 except that 600 units/kg phytase was fed. Experiment 4 was similar to Experiment 3 except that dietary phosphorus was decreased by .15%. There were no treatment effects on body weight in Experiments 1 and 2. Zinc absorption was higher in zinc-deficient birds in Experiment 1, but there were no other effects on zinc-65 absorption or retention. Body weight was increased by 1,25-(OH)2D3 in Experiments 3 and 4 and by phytase in Experiment 4. Phytate phosphorus retention was increased by phytase and 1,25-(OH)2D3 and was increased additively when both sources were fed. Dietary 1,25-(OH)2D3 increased zinc retention at times during Experiments 3 and 4, but this response was inconsistent. Phytase did not affect zinc retention. Phytase plus 1,25-(OH)2D3 increased zinc retention synergistically in Experiment 3. Bone zinc was increased by 1,25-(OH)2D3 and phytase, and there was an additive effect in Experiment 3. Plasma zinc and alkaline phosphatase were not affected. The results suggest that supplemental zinc may be decreased in a corn-soybean meal diet when phytate phosphorus utilization is enhanced.

Four experiments were conducted to study the effects of genetic strain, dietary Ca level, and feed withdrawal on growth, feed efficiency, tibia bone ash, tibial dyschondroplasia (TD), and plasma 1,25-dihydroxycholecalciferol [1,25(OH)2D3] and 25-hydroxycholecalciferol [25(OH)D3]. Experiment 1 used five strains and Experiments 2 to 4 used three broiler strains. A TD-inducing basal diet was used in each experiment. In Experiment 3, the birds were fed .60 or .95% dietary Ca, and in Experiment 4 the birds were fed the basal diet and were fed or deprived of feed for 8 h daily. In Experiment 1, Athens-Canadian Randombred and Single Comb White Leghorn chicks did not develop TD. In birds fed the basal diet alone, Peterson x Hubbard chicks had a significantly higher incidence of the most severe TD lesion than two other broiler strains in each experiment and were significantly lighter in BW in two of the four experiments. Of the three broiler strains, the incidence and average lesion score of TD was significantly higher in Peterson x Hubbard birds in Experiment 2 and was numerically highest in the other three experiments. In birds fed the basal diet, Peterson x Hubbard birds had significantly higher plasma 1,25(OH)2D3 in two of the four experiments. Both feed deprivation and .95% Ca increased bone ash and decreased the incidence and severity of TD. There were no significant differences in plasma 1,25(OH)2D3 among strains of birds deprived of feed or fed .95% Ca. In three of the four experiments, high plasma 1,25(OH)2D3 in Peterson x Hubbard birds was associated with an increase in the incidence and severity of TD.

Body weight of male Nicholas strain turkeys, castrated at 8 to 10 d of age, averaged .60, 2.20, 5.26, 8.26, and 10.83 kg at 3, 6, 9, 12, and 15 wk of age, respectively. These weights did not differ significantly from those of sham-operated control birds, but were significantly less than those of unoperated controls at 12 and 15 wk of age. Pectoralis major weights of 15-wk-old castrated turkeys were not significantly different than the sham-operated controls, but were less than those of intact controls. Pectoralis weights, expressed as a percentage of BW, did not differ among these groups. There were no differences in tarsometatarsal lengths, weight, or percentage ash among the groups. The incidence of tibial dyschondroplasia ranged from 66.7 to 80.0%, with average scores ranging from 1.00 to 1.42, with no differences among groups. Plasma testosterone concentrations of unoperated and sham-operated controls averaged .16 and .26 ng/mL at 15 wk, whereas concentrations in 7 of 12 castrates were undetectable and amounts in the other 5 castrates averaged .03 ng/mL.

Studies were conducted to determine the basic requirement of the bird for cholecalciferol in the absence of ultraviolet light by utilizing filter sleeves on fluorescent lights in the room and brooder. In Experiment 1, some pens were fitted with filter tubes and some lights were turned off. All the birds received a cholecalciferol-deficient diet. Birds with ultraviolet light excluded grew slowly, developed rickets (95%), had low plasma calcium, and low bone ash (27%); whereas birds exposed to the fluorescent light had normal growth and plasma calcium, slightly low bone ash (38%), and some rickets (12%). Experiments 2 and 3 were conducted to determine the amount of cholecalciferol that must be added to the diet under conditions in which ultraviolet light was excluded. In Experiment 2, the highest level of cholecalciferol fed was 400 ICU/kg. This level was not sufficient to permit the chickens to have weight gain or bone ash equal to the birds receiving the ultraviolet light. The birds receiving 400 ICU/kg of diet also had a 77% incidence of rickets compared with 20% for the birds receiving ultraviolet lights. In Experiment 3, when birds received 800 or 1,600 ICU/kg of cholecalciferol in the diet, they grew and were comparable to those receiving ultraviolet light for the criteria measured.

These studies were conducted to determine if supplementation of a corn-soybean meal diet with 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] would increase the utilization of natural phytate phosphorus by broiler chickens. Two experiments were conducted to evaluate the effect of dietary 1,25-(OH)2D3 in the presence and absence of supplemental phytase and at several dietary levels of inorganic phosphorus supplementation. The criteria measured in these studies were weight gain, gain:feed ratio, bone ash, rickets due to phosphorus deficiency, plasma calcium and phosphorus and retention of calcium, phosphorus and phytate phosphorus. In the first experiment, the types and amounts of fecal inositol phosphates were determined by HPLC, and the total fecal phytate was determined by the classic FeCl3 precipitation technique. In the first experiment, the addition of 1,25-(OH)2D3 to the diet in the presence of dietary phytase resulted in greater 9-d weight and bone ash and lower incidence of rickets; the retention of total fecal phytate and phytate phosphorus was greater than in controls. The second experiment was a complete 2 x 2 x 2 factorial design [phosphorus levels x phytase x 1,25-(OH)2D3]. The addition of 1,25-(OH)2D3 alone to the diet resulted in greater 9-d weight and bone ash, lower incidence of rickets, and greater retention of total calcium and phosphorus and phytate phosphorus. The highest retention of phytate phosphorus (79.4%) was obtained when both phytase and 1,25-(OH)2D3 were present in the diet. The possible mode of action and importance of these results in many areas of nutrition and environmental science are discussed.

A series of experiments was conducted to investigate interactions of dietary calcium levels with ultraviolet light, cholecalciferol (D3), 1,25-dihydroxycholecalciferol [1,25-(OH)2D3], dietary protein, and a synthetic zeolite on the development of tibial dyschondroplasia in broilers. A basal diet low in calcium, high in phosphorus and chloride, and known to promote a high incidence of tibial dyschondroplasia was used. The chicks received ultraviolet radiation from fluorescent lights in addition to 1,100 ICU/kg (27.5 micrograms/kg) of D3 in the basal diet when these were not experimental variables. Regardless of whether the calcium level was low (.65%) or adequate (.95%), the incidence of tibial dyschondroplasia was significantly lower in chicks receiving ultraviolet radiation or dietary vitamin D3 levels well above the required amounts. The addition of 10 micrograms/kg of 1,25-(OH)2D3 to the diet when calcium levels varied from .45 to .95% resulted in a reduction in the incidence of tibial dyschondroplasia and increased tibial bone ash when dietary protein levels were 18 or 22%. The addition of 1% synthetic zeolite to the diet did not influence the incidence of tibial dyschondroplasia when the diet contained widely varying dietary calcium levels (.65 to 1.81%) and .73% phosphorus.

The first experiment was a central composite rotatable design with calculated calcium levels of 6.2, 7.0, 9.0, 11.0, and 11.8 g/kg diet and total phosphorus levels of 5.2, 6.0, 8.0, 10.0, and 10.8 g/kg diet (2.8 g phytin-P/kg by analysis). This design involved three replicates for each rotatable point and fifteen replicates of the central point. The second experiment was a 4 x 4 factorial design with calculated Ca levels of 8.0, 10.0, 12.0, and 14.0 g/kg diet and calculated total P levels of 7.0, 9.0, 11.0, and 13.0 g/kg diet (2.5 g phytin-P/kg by analysis). There were four replicates for each treatment. In both 16 d experiments maize-soya-bean diets were used and each replicate consisted of one pen containing 10-d-old broad-breasted, white tom turkeys. The Ca and total P requirements for optimum growth were estimated to be 12.5 and 10.0 g/kg diet respectively. Bone ash was adequate at these levels of Ca and total P, but maximum bone ash was not achieved until much higher levels of Ca and total P were employed. At the required levels of Ca and total P for growth the incidences of Ca- and P-deficiency rickets were very low. There were no treatment effects on feed efficiency. Increasing dietary Ca decreased the incidence of the Ca-deficiency lesion. There was a quadratic response due to dietary total P on both P-deficiency rickets and plasma dialysable P; intermediate levels of dietary P resulted in low incidence of the P-deficiency lesion and high levels of plasma dialysable P. There was a strong negative correlation between the incidence of P-deficiency rickets and plasma dialysable P. Percentage retention was very low at high levels of dietary P and low levels of Ca which corresponded with slightly higher P-deficiency rickets and low plasma dialysable P. No such obvious relationships existed between Ca retention, incidence of Ca-deficiency rickets, and plasma Ca. The incidence of tibial dyschondroplasia was very low in the present study. There were pronounced dietary treatment effects on phytin-P retention; at 14 d percentage phytin-P retention treatment means ranged from 18 to 46 in Expt 1 and from 0 to 40 in Expt 2 with the highest retention of phytin-P at low levels at both Ca and total P.

Two experiments were designed to determine the effect of dietary boron on broiler cockerels and four experiments were conducted to determine whether an interaction exists among dietary boron, cholecalciferol, and calcium. The parameters measured were weight gain, feed efficiency, tibia bone ash, rickets, tibial dyschondroplasia, and plasma minerals. All experiments were conducted with tibial dyschondroplasia-inducing basal diets fed to broiler cockerels from 1 to 16 days of age. Experiments 1 and 2 had four levels of dietary boron (0, 20, 40, and 80 mg/kg (Experiment 1) and 0, 5, 10, and 20 mg/kg (Experiment 2). Boron had no effect on weight gain, feed efficiency, or plasma minerals in either experiment. In Experiment 2, increasing levels of boron had no influence on tibial dyschondroplasia but did exert a quadratic effect on bone ash with 5 and 10 mg/kg boron increasing bone ash. In Experiment 1, bone ash and the incidence of tibial dyschondroplasia were unaffected, but the severity of tibial dyschondroplasia linearly increased by increasing boron levels. Experiments 3 to 6 had a 2 x 2 x 2 factorial arrangement of treatments with calcium at .65 and .90%, cholecalciferol at 110 and 1,100 ICU/kg, and boron at 0 and 40 mg/kg (Experiments 3 to 5) or 0 and 3 mg/kg (Experiment 6). The higher levels of calcium and cholecalciferol improved weight gain, decreased the incidence of rickets, and decreased the incidence and severity of tibial dyschondroplasia. Feeding cholecalciferol at 1,100 ICU/kg increased plasma calcium and plasma dialyzable phosphorus and decreased plasma magnesium. Calcium at .90% had no effect on plasma magnesium or plasma dialyzable phosphorus and increased plasma calcium only in Experiment 4. The only response to boron in Experiments 3 to 6 was a boron effect and a boron by cholecalciferol interaction on bone ash in Experiment 3, in which boron reduced bone ash at .65% calcium and 110 ICU/kg cholecalciferol. From these experiments, there is no indication that an interaction among boron, cholecalciferol, and calcium exists in broiler cockerels.

Three experiments were conducted to investigate the effect of zeolites on laying hens (Experiments 1 and 2) and broiler chickens (Experiment 3). Each experiment used corn and soybean meal-based practical diets. Experiment 1 was a 90-day trial and used 200 40-wk-old laying hens. The basal diet contained 2.75% calcium and .7% total phosphorus. The dietary treatments were the basal diet and the basal diet plus 1.5% synthetic zeolite (SZ; Ethacal). Experiment 2 was a 56-day trial and used 360 36-wk-old laying hens. The dietary treatments were .12, .22, .32, and .42% nonphytin phosphorus with and without 1.0% SZ and 1.0% natural zeolite (NZ; Zar-Min). All diets contained 3.5% calcium. Experiment 3 utilized 240 broiler cockerels from 1 to 16 days. The dietary treatments were two calcium levels (.65 and 1.0%) with and without 1.0% supplementary SZ and NZ. In Experiment 1, egg specific gravity was significantly increased with SZ supplementation. Egg weight and egg production were unaffected. Phytin phosphorus retention and plasma dialyzable phosphorus were significantly reduced by SZ. In Experiment 2, egg specific gravity was not affected by SZ or NZ. Egg weight, egg production, plasma dialyzable phosphorus, and the retention of phosphorus and phytin phosphorus were significantly reduced by SZ with the effect on egg weight and egg production being the most severe at the lower levels of dietary nonphytin phosphorus. Natural zeolite had no effect on egg weight, egg production, plasma calcium, plasma phosphorus, or on the retention of calcium, phosphorus, and phytin phosphorus. In Experiment 3, weight gain and percentage tibia bone ash were significantly reduced by SZ. The SZ had no effect on the incidence and severity of tibial dyschondroplasia. Weight gain, feed efficiency, and the incidence and severity of tibial dyschondroplasia were significantly reduced and the percentage bone ash significantly increased by 1.0% calcium. Natural zeolite significantly improved feed efficiency and had no effect on any other parameter measured.