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Two continuous culture fermentation experiments were used to determine ruminal microbial fermentation in the presence of monensin (Exp. 1) or lasalocid (Exp. 2) with different dietary concentrations of Mg and K. In each experiment, eight 500-ml continuous culture fermentors were supplied with late-cut coastal bermudagrass (80%) and cellulose (20%) as substrate during five trials with two levels of Mg (.07 and .14%), K (.6 and 2.5%) and either monensin (Exp. 1; 0 and 20 mg/kg) or lasalocid (Exp. 2; 0 and 20 mg/kg) in a 2 × 2 × 2 factorial arrangement of treatments (each trial served as a replication). Substrate was added every 8 h (5 g/fermentor) for 5 d and digesta samples were collected every 2 h for 6 h and at 20 h for volatile fatty acid (VFA) analysis on d 6. In Exp. 1, monensin decreased (P<.05) the acetate:propionate ratio (A:P) from 2.98 to 2.22. A Mg × monensin interaction was observed for the molar percentage of acetate and propionate (P<.05). There was a 4.8% reduction in acetate (mol/100 mol) when monensin was fed with .07% Mg and a 12.6% decrease (P<.01) when fed with .14% Mg compared with diets not containing monensin. Propionate (mol/100 mol) increased 14% when monensin was fed with .07% Mg and 32% (P<.001) when fed with .14% Mg compared with diets not containing monensin. Potassium did not affect VFA concentrations in the presence of monensin or Mg. In Exp. 2, lasalocid decreased (P<.01) the A:P ratio from 3.53 to 2.86. There was a Mg × lasalocid interaction (P<.01) for butyrate (mol/100 mol). Lasalocid lowered (P<.001) butyrate (mol/100 mol) 35% when fed with .07% Mg and 53% when fed with .14% Mg. A lasalocid × K interaction existed for propionate (P<.10) and butyrate (P<.05;mol/100 mol). Lasalocid increased (P<.10) propionate molar proportion 30% when fed with .6% K and 41% when fed with 2.5% K compared with diets not containing lasalocid. Butyrate molar proportion decreased (P<.05) more when lasalocid was fed with 2.5% K than when fed with .6% K. These data suggest that previously reported inconsistent results with monensin and lasalocid supplementation may have been due to these ioniphores' interactions with other nutrients. Furthermore, these results suggest that the efficacy of monensin and lasalocid in altering the VFA concentrations of ruminal fermentation might be enhanced by optimizing other nutrients.

Sixty dry, nonpregnant, mature cows of five breeds (Angus, A; Brahman, B; Hereford, He; Holstein, Ho and Jersey, J) and their F, crosses (AB, AHe, AHo, AJ, BHe, BHo, BJ, HeHo, HeJ and HoJ, reciprocal crosses pooled) were used in a 51-d experiment (four cows/breed group) to determine apparent and true digestibility of magnesium (Mg). Cows were greater than 10 yr old and averaged 535 kg. Cows were individually fed daily for four consecutive periods at each of four intake levels in a replicated Latin-square design, with replicate being breed group. The diet was primarily cottonseed hulls, cottonseed meal and ground milo with a Mg content of .30% as fed. Intake levels were 50, 83, 117 and 150% of each cow's estimated maintenance energy requirement. Period 1 consisted of 10 d adjustment and 7 d for each subsequent period followed by a 5 d collection of fecal samples. Fecal samples were collected daily at randomly assigned times. Feed and feces were analyzed for indigestible neutral detergent fiber to determine fecal output and for Mg to determine apparent Mg digestibility. True digestibility of Mg was predicted from the regression of apparent Mg absorption on Mg intake. Apparent digestibility of Mg increased (P<.05) from 13.2 to 43.4% as intake level increased from 50 to 150%. The apparent digestibility of Mg in AHe, J and HoJ was lower (P<.05) than that of B, AB, BHe, BHo, HeJ and BJ. The predicted true digestibility of Mg across all breed groups was 61.1%. Predicted true digestibility of Mg was higher (P<.05) for B, BHo, A and HeHo than He, HeJ, BHe, J and Ho. The estimated endogenous excretion of Mg ranged from 1.8 to 10.5 g/d. Holstein-Jersey and HeHo had a larger (P<.05) quantity of estimated endogenous Mg excreted than AB, He, Ho, HeJ and BHe. Differences observed between breeds of cattle for grass tetany may be partially related to these changes in Mg digestibility.

Body compositions of 40 Angus, 20 Angus-Hereford and 20 Angus-Holstein spring-calving cows were determined by deuterium dilution at the initiation and at the end of the winter feeding period. For the winter feeding period, cows were allotted within breed to metabolizable energy (ME) levels of 12.9 or 18.0 Mcal/ head daily. Weight (W), length, height, heart girth and condition score were measured on each cow before body composition determinations. Regressions were conducted within breed-body composition determination time groups to evaluate linear measurements and condition score as predictors of percentage empty body fat (PEBF) of beef cows. Regressions for Angus and Angus-Hereford cows were similar, but regressions for Angus-Holstein cows differed from those for Angus or Angus-Hereford cows. The best simple regression for the Angus-Holstein cows accounted for only 3% of the variation in PEBF. For the Angus and Angus-Hereford cows, condition score was the best estimator of PEBF (r = .66,P<.01). Weight: height ratio was correlated .58 (P<.01) with PEBF; however, weight alone was correlated .54 with PEBF. Regressions with W2.0, W•75and W did not improve R2values over those obtained with W1.0. Log and square root transformations of linear measurements did not improve ability to estimate PEBF. Multiple regressions did not significantly improve R2 values over that of the simple regression of PEBF on condition score. Results of this study suggest that linear measurements are not superior to visual appraisal as estimators of body composition of beef cows.

Experiments were conducted to determine the effects of whole plant grain sorghum silage processing and dietary lasalocid on stocker calf performance, digestibility and rumen fermentation. Two silage treatments and three concentrations of lasalocid (0, 33 and 49 ppm) were examined in a 100-d growth trial. Lasalocid at 33 ppm depressed feed intake of steers without affecting weight gain and, therefore, improved feed efficiency. Lasalocid at 49 ppm did not improve feed conversion over that observed in controls. Both concentrations of lasalocid increased rumen propionic acid and decreased acetic acid levels. Lasalocid did not affect ruminai concentrations of isobutyric, valeric or isovaleric acids. Dry matter intake and animal weight gain in the growth trial were greater for steers fed the nonprocessed whole plant grain sorghum silage (NPS) with grain in the whole form than for those fed processed silage (PS) with the grain rolled before ensiling. Feed efficiency was similar for steers fed the two silage treatments. Processing treatment did not influence ruminai acetic propionic, isobutyric or isovaleric acid proportions. In a digestion trial, post-ensile rolling of the grain and stover of whole plant grain sorghum silage increased (P<.05) in vivo starch digestion above levels observed for PS or NPS silages. Digestibilities of dry matter, organic matter, crude protein and acid detergent fiber were similar for all silage treatments.

The function of end products of silage fermentation, added initially at levels commonly present in fermented forage, in directing or limiting fermentative activity was evaluated using Plexiglas laboratory silos. Additions, on a dry matter basis, included .7% ethanol, .9% acetic acid and 4.7% lactic acid to chopped corn plant material, singly and in all combinations in a 23factorial arrangement of treatments using 24 laboratory silos with three silos/treatment. Lactic acid added singly stimulated nonlactic acid fermentation. It increased gas production, wet matter loss, energy loss and ethanol levels to values that were 1.6-, 1.3-, and 2.2-fold those found in untreated silage. Lactic acid caused a 41% reduction in acetic acid production. Final lactic acid levels were elevated slightly and pH was reduced. Acetic acid alone inhibited fermentation, since it decreased production of lactic acid and ethanol by 18 and 30% and reduced wet matter and energy losses by 18 and 67%. Ethanol added independently increased lactic acid production 25%, reduced energy loss 52%, but did not alter acetic acid or ethanol production since the resulting silage ethanol levels were elevated to the extent of the initial addition. Responses to combinations did not parallel independent additions. The combination of acetic and lactic acids essentially eliminated their production, since final levels were about equal to the amounts added and reduced gas production to 35% of that from control silos. In this treatment acetic acid negated in part the stimulatory effect of lactic acid on ethanol production, reduced wet matter loss as occurred with acetic alone and resulted in an energy loss that was similar to that for control silos. Other combinations appeared to result in unfavorable responses. Lactic acid added with ethanol reduced production of lactic and acetic acids, increased energy losses and elevated both gas and ethanol productions. While acetic acid or ethanol added independently reduced energy losses, when used in combination energy loss was similar to controls. The combination of lactic and acetic acids with ethanol reduced production of gas, but energy losses were about twice those for control silos. Regulation of fermentation via acetic acid, ethanol and lactic acid was only indirectly related to pH suggesting selective microbial action of these end products on fermentation processes.

An energy balance experiment was conducted to examine the effects of monensin on energy partitioning of cattle fed corn silage diets. One hundred and thirty Hereford steer feeder calves (average initial weight 247 kg) were used. Cattle were fed ad libitumfor 211 days or limit-fed for 253 days. Carcass specific gravity was measured on all cattle for calculation of energy and tissue retention. Conclusions on energy utilization were based on linear regressions of energy retention on metabolizable energy and dry matter intake above maintenance, with comparisons to semilog calculations evaluated. Rates of live weight gain for ad libitum-fedcattle were similar with and without monensin (920 vs923 g/day), while dry matter consumption was significantly reduced (5.91%) with monensin. Feed conversion was improved (5.84%) with monensin. Terminal body composition and total energy retained were not significantly altered by monensin. Limiting energy intake reduced daily rates of fat deposition more (−47.3%) than it reduced protein (−25.1%). Limit-fed steers had 10% less fat than ad libitumfed steers at equal empty body weights. Monensin tended to increase rates of protein and decrease rates of fat deposition in limit-fed cattle, and it induced a change (P<.08) in composition of growth. Monensin increased the apparent efficiency of energy use for maintenance by 5.7% but did not alter the efficiency of energy use for growth. Dry matter needed for maintenance was reduced by 5.4% with monensin. These data indicate that monensin may decrease maintenance requirements and (or) increase efficiency of diet energy use for maintenance.

A growth and energy balance study was conducted to investigate the effects of limestone and monensin on corn silage net energy value. One-hundred and thirty Hereford steer calves (average initial weight, 240 kg) were allotted to 13 groups; an initial slaughter group (“initial” cattle) and 12 groups fed in a 2 × 2 × 2 factorial design (“fed” cattle). Factors were: (1) untreated or 1% limestone (CaCO3)-treated corn silage, (2) no monensin or added monensin and (3) ad libitumor 70% of ad libitumintake, with two groups fed ad libitumand one group limit-fed each treatment. Where indicated, 1% CaCO3was mixed with chopped corn plant material at ensiling, and monensin was provided in the protein mineral supplement. Body composition, energy and tissue balance were calculated from measurements of carcass specific gravity taken on “initial” cattle and “fed” cattle at slaughter. Recovery of silage wet matter in barrel silos was similar whether silages were treated or not. While neither limestone nor monensin altered rate of gain, dry matter intake was reduced (P<.01) 7.8, 12.2 and 18.7% with monensin, limestone and the combination, respectively. Concurrent improvements (P<.05) in dry matter to gain ratio were 5.8, 9.1 and 14.3% for monensin, limestone and both, respectively. Monensin, limestone and the combination increased average net energy value [NEm+ NEg]/2 by 8.8, 9.6 and 15.4%. Restricting energy by limit feeding, even on this forage diet, reduced daily rates of protein deposition by less than 14% while decreasing (P<.01) fat accretion by over 43%. As a result, cattle fed ad libitumwere 21% fatter (P<.01) than limit-fed cattle (30.87 vs25.48% fat) at 352 kilograms. Level of nutrition regulated composition of growth, and the effects of limestone treatment and monensin supplementation on corn silage net energy value were additive.

Two feedlot studies were conducted with 96 Hereford steers to assess the relationship between selenium adequacy and protein requirements of growing and finishing cattle. The first study was a 98-day growing trial with feeder steers as they gained from 230 to 340 kilograms. Diets contained 55% corn silage (dry matter basis) with shelled corn and were supplemented with soybean meal and sodium selenite to provide three levels of protein, each with basal or added selenium. Two lots of eight cattle each were fed each diet. After the growing study, the cattle were reassigned to a 112-day finishing study (340 to 480 kg) and fed diets including whole shelled corn and 7% corn silage, with basal or added protein as soybean meal or linseed meal with or without supplemental selenium as sodium selenite. In the growing study, cattle fed the three protein levels consumed 676, 858 and 1026 g crude protein/day and gained 1.01, 1.09 and 1.23 kg/day over the 98 days. Feed conversion averaged 5.76, 5.60 and 5.07. Rate (P<.01) and efficiency of growth were improved 23 and 12%, respectively, for cattle fed the 16.5% protein compared to those fed the 11.6% protein diet. Feed intakes were greater (P<.05) for cattle fed 14.1 and 16.5% protein diets than for those fed the 11.6% protein diet. Plasma urea nitrogen increased (P<.01) with protein level (7.8, 10.7, 15.2 mg/100 ml). Cattle fed each diet responded positively to selenium in rate and efficiency of gain, with the greatest response observed for those fed the lowest protein diet. Plasma selenium levels were marginal for cattle fed basal diets, indicating a deficiency, and increased (P<.01) about twofold with supplemental selenium. During the finishing phase, supplemental selenium added inorganically as sodium selenite or organically in linseed meal did not alter performance. Although liver selenium levels increased (P<.01) when either sodium selenite or linseed meal was added, the combination resulted in no further increase above levels observed for cattle fed basal selenium linseed meal diets. Response in daily gain to supplemental protein was significant, and performance with either soybean meal or linseed meal was similar. Protein intake averaged approximately 700 and 880 g/day for basal- and soybean meal-supplemented cattle. Gains of cattle previously fed 11.6, 14.1 and 16.5% protein during the growing study differed (P<.002) during the finishing study, with rates of 1.31, 1.24 and 1.12 kg/day, respectively. The interaction of growing-finishing phase protein levels was not significant. These data indicate that for Hereford cattle growing from 230 to 340 kg and fed corn grain-corn silage diets, the crude protein requirement approaches 1,000 g/day, while for finishing cattle over 340 kg and fed shelled corn, the requirement is largely for maintenance and is between 700 and 880 g/day. These data also indicate that selenium levels are most critical during early stages of growth and when cattle are fed diets marginal or deficient in protein.

Sixty-four steer calves were individually fed in a 181-day experiment to determine their gain, feed efficiency, plasma urea-N and seminal vesicle response following implantation with 30 mg of either stilbene, estriol, estrone, β-estradiol, α-estradiol or diethylstilbestrol (DES). Half of the steers were fed a constant level and the remaining half were fed a declining level of supplemental protein providing 1.5, 1 and .5 times that of the constant level of supplemental protein.Gain and dry matter efficiency were stimulated by β-estradiol (24 and 13%, respectively) and DES (12 and 9%, respectively), whereas the other compounds did not result in any stimulation. The plasma urea-N response of these steers paralleled the gain and efficiency response. Thus, it is concluded that marked estrogenic potency of compounds is required for gain and efficiency stimulation in cattle. On the other hand, the seminal vesicle gland was stimulated 62 and 33% as much by estriol and estrone, respectively, as observed with DES or β-estradiol. Thus it appears that the seminal vesicle gland can be stimulated in size by compounds that do not elicit a gain response in steers.Performance of these steers was not altered by feeding a declining level compared to a constant level of supplemental protein. Plasma urea-N levels indicate that 7 to 8 mg/100 ml may be the minimum level compatible with maximum feedlot performance.

Corn grain was ensiled in whole kernel or rolled forms, at harvest or after drying and reconsitution to moisture levels of 21.5, 27.5 and 33.1%. As moisture contents increased, energy losses increased and pH values decreased. Molar percentages of acetic, propionic and butyric acids in the ensiled corn grain averaged 5.2, .8 and 1.6%. Rolled corn and corn ensiled immediately following harvest at 33.1% moisture had the highest butyric acid concentrations. Lactic acid and ethanol concentrations were highest for corn ensiled at 27.5 or 33.1% moisture. Molar percentages of lactic acid were higher and molar percentages of ethanol were lower for corn ensiled at 27.5 or 33.1% moisture than for corn ensiled at 21.5% moisture. In this study energy losses were minimized by ensiling rolled corn grain at moisture contents of 21.5 or 27.5%.

A study was conducted to evaluate the effectiveness of NaHCO3and trona in beef cattle diets. Trace element (n=28) analysis revealed no toxicological or safety concerns with the use of trona. Trona was more (P<.05) soluble in ruminal fluid than Na2CO3, and NaHCO3and had greater (P<.05) buffering capacity (9.6 meq/g) than NaHCO3(6.1 meq/g) but less (P<.05) than Na2CO3(11.1 meq/g). Calcium carbonate was insoluble and did not buffer ruminal fluid. Six yearling (avg 272 kg) Hereford × Angus steers, each with ruminal, duodenal and ileal cannulas, were fed 50:50 (cracked corn-based concentrate:cottonseed hulls) or 90:10 concentrate diets with no buffer, 1% NaHCO3or with 1% trona. Intake, across all treatments, averaged 2.4% of body weight. Propionate (mmol/liter) increased (17.6 vs 13.5; P<.05) and butyrate decreased (3.5 vs 5.2; P<.05) with trona in the 90:10 diet as compared with no buffer. Propionate (16.8) increased (P<.05) with NaHCO3in the 90:10 diet. Average ruminal pH was greater (P<.05) in 90:10 diets with trona or NaHCO3than with no buffer (5.61, 5.61 vs 5.55); duodenal pH was greater (P<.01) with trona than with no buffer (2.66 vs 2.55). Trona reduced ruminal pH-hours (P<.05) and pH-area (P<.12; time and area below mean pH of control) below control for both concentrate levels. While both NaHCO3and trona improved volatile fatty acid patterns, trona was more effective than NaHCO3in modifying acid-base balance, thus providing a more stable ruminal environment by minimizing very low pH conditions.

Six yearling Hereford × Angus steers (avg 272 kg), each with ruminal, duodenal and ileal cannulas were used in a 6 × 6 Latin-square metabolism trial to evaluate the impact of NaHCO, and trona (a ground, nonrefined ore with chemical composition NaHCO3-Na2CO3-2H2O) on site and extent of digestion of nutrients in the digestive tract. The diets were 50:50 or 90:10 (cracked corn-based concentrate:cottonseed hulls) with no buffer, 1% NaHCO3, or 1% trona. Intake, across all treatments, averaged 2.4% of body weight. Dry matter (DM) and starch digestibility (via indigestible acid detergent fiber) before the duodenum was decreased (P<.10) with trona in the 50:50 diet. Digestibility of DM, crude protein and starch before the ileum were greater (P<.05) in the 90:10 diet vs 50:50 diet. Total tract digestibility was similar across buffer treatments in the 90:10 diet. Addition of NaHCO3increased (P<.05) digestibility of dry matter and cell solubles in the 50:50 diet. Organic matter and crude protein digestibility were also increased (P<.10) with NaHCO3. Apparent crude protein and cell solubles digestibility were greater (P<.10) with trona than NaHCO3 in the 50:50 diet. This trial indicates that buffers provide overall enhancement of diet digestibility in mixed grain/roughage diets.