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Two experiments were conducted using four strains of Leghorn pullets, namely Babcock, DeKalb, H & N, and Shaver. Pullets were grown on conventional or low protein diets fortified with additional amino acids. At 18 wk of age, 64 pullets from each strain and diet treatment were transferred to individual laying cages, using eight replicate groups of four adjacently caged birds. In a second experiment, pullets from the four strains were selected based on body weight at 18 wk of age (approximately 1,270 vs 1,650 g). Each weight group and strain was again represented by eight replicate groups of four birds. In Experiment 1, there were no strain or rearing diet effects on egg production (P > 0.05). Rearing diet had little long-term effect on any adult characteristics. There were significant (P < 0.01) strain effects on body weight, feed intake, and egg weight, although these were independent of rearing diet. In Experiment 2, regardless of bird strain, the pullets with smaller body weight matured more slowly (P < 0.01) and produced less total egg mass to 70 wk age (P < 0.05). These smaller birds ate less feed and produced smaller eggs (P < 0.01). There were strain effects, independent of 18-wk body weight, for egg weight and eggshell quality (P < 0.01). It is concluded that minor strain differences exist with respect to response to juvenile nutrition, although such effects are only evident in early lay. All strains of bird remain small, 18-wk body weight is reduced, and these birds subsequently eat less feed and produce smaller eggs.

Two experiments were undertaken to study the response of White Leghorn hens to low dietary phosphorus levels from 18 to 64 wk of age. A corn-soybean meal diet containing .2% available phosphorus gave similar performance, up to 32 wk of age, as a similar control diet containing .4% available phosphorus. Beyond 32 wk, although shell quality and average egg weight were similar, egg production was significantly reduced with the lower phosphorus diet. Phosphorus excretion (grams per bird per day) averaged .47 g for .4% vs .28 g for .2% available phosphorus when measured at 28 wk of age. In a second experiment identical procedures and bird number as used in Experiment 1 were employed with the exception that the test diet contained .3% rather than .2% available phosphorus. No differences were noted for any of the production variables measured between the .4 and .3% available phosphorus diets. Phosphorus excretion data collected at 25, 32, 44, and 60 wk of age showed a decrease of approximately 20% for hens receiving the lower phosphorus diet. Indeed the overall average for phosphorus excretion for the lower phosphorus diet was calculated to be identical to the 20% lower total phosphorus content of this diet (.59 vs .47%).

White Leghorn chicks were fed corn-soybean meal diets containing 20, 17, 14, and 11% protein, with similar levels of energy, from hatch to 16 wk of age. Body weights at 16 wk were similar for pullets fed the 20 and 17% protein diets, but were reduced by 11 and 27% for birds fed the 14 and 11% protein diets, respectively, as compared with the 20% protein diet. At 16 wk of age, all birds were placed on a common 17% protein laying diet. Pullets fed the 14 and 11% protein laying diets were slightly slower coming into production, however, by 28 wk of age egg production was similar for all four growing treatment groups and remained so until the end of the experiment. Average egg weight was similar for pullets fed the two higher levels of protein during the growing period and significantly lower for those pullets fed the 11% grower diet for all except the 28- and 32-wk periods. Pullets fed the 14% grower diet produced eggs with average weights significantly lower than those for the higher protein diets from 40 to 58 wk of age. Although the results might be interpreted as indicating that higher protein growing diets result in body protein reserves that subsequently enhance egg size, it is more likely that the pullets consuming lower protein diets produce smaller eggs because they have smaller body weights.

Two experiments were conducted to investigate the effect of supplemental niacin on laying hen performance and liver fat and egg cholesterol content. In Experiment 1, 16 replicate groups of four adjacently caged birds were fed corn and soybean meal diets calculated to contain 22, 44, 66, or 132 mg supplemental niacin/kg (23.2, 38.7, 57.0, and 143 mg/kg niacin by analysis). Egg production, egg weight, feed intake, and eggshell quality were assessed each 28 days through a 364-day trial period. After 280 days, cholesterol content on three eggs per replicate was measured. At the end of the study, one bird per replicate was killed for subjective scoring of liver fat content. In Experiment 2, 24 birds from the control treatment (22 mg/kg supplemental niacin) of Experiment 1 were retained and fed for a subsequent 28-day period. Over this time, eight birds were each fed diets containing 22, 522, or 1,022 mg/kg supplemental niacin. Egg cholesterol content was measured in eggs collected on the last 3 days of the study. In Experiment 1, birds fed 66 or 132 mg/kg supplemental niacin/kg produced more eggs (P less than .05) than birds fed 22mg/kg. Niacin supplementation affected shell quality (P less than .05). Dietary niacin level had no effect on egg cholesterol content of liver lipid evaluation. In Experiment 2, supplementary niacin levels up to 1,022 mg/kg, which more closely stimulates therapeutic levels used for humans, again failed to affect egg cholesterol content.

Leghorn pullets of a commercial strain were cage-reared at densities of 293 or 586 cm2/bird. Diet treatments consisted of a control step-down protein program, a reverse-protein program, and two treatments involving 18% crude protein throughout rearing with modification of texture and energy concentration according to bird age. Thus, one treatment involved a crumbled low-energy diet to 10 weeks, followed by a crumbled high-energy diet to 16 weeks, while the alternate series involved a mash low-energy diet to 10 weeks followed by the crumbled high-energy diet to 16 weeks. Birds were weighed periodically throughout rearing and, when they were subsequently moved to laying cages, light was immediately increased from 8 to 14 hr. Irrespective of diet treatment, the more liberal density of 586 cm2/bird resulted in a 5 to 8% increase in feed intake (P less than .01). However, this increased intake was not associated with increased body weight (P greater than .05), and as confirmed by carcass analysis, it is assumed that this increased nutrient intake relates to increased maintenance requirement associated with bird activity. Birds offered the crumbled vs. mash high-energy diet to 10 weeks of age, consumed more feed (P less than .01), although change of diet texture from mash to crumble at 10 weeks failed to stimulate appetite. Also, birds reared on either the step-up energy programs were similar in weight to control-reared birds at 16 weeks of age.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparative study was conducted to determine the effect of two varieties of rapeseed meal at 10 and 20% levels in the diet on the productive performance, organ weights and liver lesions of two commercial strains of laying hens. The double-low (Brassica napus 1788) rapeseed meal appeared to be superior to Span meal (Brassica campestris) at the 10% level in maintaining egg production, feed efficiency, thyroid weight and body weight gain. However at the 20% level the productive performance was decreased in all the hens except the thyroid weights in the double-low group. Mortality caused by haemorrhagic liver syndrome was significantly higher among birds fed rapeseed meals than in the controls and was higher in the Span-fed groups than in those receiving the double-low variety. The two strains of birds showed no difference in mortality due to haemorrhagic liver syndrome. It was suggested that the lower level of glucosinolates in the double-low variety was responsible for the superiority of this meal over the Span meal.

An experiment was undertaken to test the response of dwarf broiler pullets when fed on two planes of nutrition in the growing period and fed either a 17 or 19% protein diet in the breeder house. Pullets offered 20% more feed in the growing period were heavier at 21 weeks of age and reached 50% egg production 2 weeks earlier than birds fed the regular diet. Pullets fed 20% more feed in the growing period and full-fed to 26 weeks in the laying house, gained appreciably more weight, and although they came into production faster, were less persistent in lay than birds fed the regular diet. There was no difference in egg production, egg size, or body composition of dwarfs fed 17 or 19% breeder diets.

Two trials were conducted to note the effect of immature body size of leghorn pullets on subsequent laying performance, and in particular, egg size. In Trial 1, birds were classified as small, medium or heavy at 15 wk of age (997, 1,100, and 1,226 g, respectively). In Trial 2, segregation at 19 wk resulted in groups with mean weights of 1308, 1411, and 1564 g, respectively. In each trial, weight groups were represented by 40 replicate groups of four individually caged birds. Original weight groupings were maintained throughout the trials (P less than .05). In both trials, immature weight classification had a consistent effect on both feed intake and egg weight (P less than .05); larger birds consumed more feed while producing larger size eggs. In Trial 1, medium weight birds produced more eggs over the 52 wk. Similarly, smaller weight birds produced more eggs than did heavy birds (P less than .05). In Trial 2, weight grouping had no overall effect on egg production, although during the 19 to 23-wk period, heavy birds produced more eggs (P less than .05). It is concluded that immature body weight (15 to 19 wk age) can influence egg weight and that this relationship is linked to levels of nutrient intake. Each 100-g increase in body weight was associated with approximately 3.5 g increase in feed intake and 1.2 g increase in egg weight.

A total of 192 Single Comb White Leghorn pullets were divided into three groups to study the effect of heat stress and diet composition on feed intake and laying performance at 21, 25, and 33 weeks of age. For each age group all birds were fed a control diet [17.1% crude protein (CP), 2770 kcal metabolizable energy (ME)/kg] for a 7-day period. During this time they were kept at a temperature of 18 C. The temperature was then immediately increased to 35 C, and groups of 16 birds offered either the control diet, a high protein diet (43.5% CP), a high energy diet (3371 kcal ME/kg), or a diet of high nutrient density (28.3% CP, 2842 kcal ME/kg, and 6.5% Ca) for a 3-day period. After the 3-day test period, temperature was returned to 18 C, although birds were still offered the experimental diets for an additional 4 days prior to returning to the control diet. Production parameters were measured for individual birds. Feed consumption, egg production (except for the 21-week-old birds), egg weight, and egg shell thickness decreased (P less than .05) with heat stress. Increases in energy and calcium intake helped partially to maintain normal egg production, egg weight, and egg shell deformation. Egg weight and egg shell deformation returned to pretest levels within an 8-week postexperimental period. With the exception of those birds receiving the control and high nutrient density diets at 21 weeks of age, data collected over the test periods showed that heat stress caused a significant reduction (P less than .05) in liveweight birds.

Leghorn pullets of a commercial strain were subjected to a conventional light program of constant photoperiod or an intermittent programming involving, during the house of conventional "lights-on", 45 min light (L): 15 min dark (D) from 24 to 27 weeks of age; 30 min L:30 min D from 28 to 35 weeks; and 14 min L:45 min D from 36 weeks to the duration of the trial. Each light treatment was tested with 12 replicate groups of 14 individually caged birds housed in adjacent rooms, with all birds fed a standard 15% crude protein, 2750 kcal ME/kg diet. Intermittent lighting resulted in a significant (P less than .05) reduction in feed intake and a consistent but nonsignificant (P less than .05) reduction in egg production. Egg size, egg shell quality, and albumen quality, as assessed by Haugh units, were not affected by light treatment. Due to the effect on egg production, it is concluded that intermittent lighting programs should not be initiated close to time of peak egg production.

Leghorn pullets were cage reared to 15 or 19 wk of age in environmentally controlled rooms that provided either 8 h or 14 h of light per day. In Experiment 1, birds were moved to laying cages at 15 wk of age and subjected to either 14 h light (L): 10 h (D) dark or ahemeral 14L:14D photoperiods. Feed intake, egg weight, shell quality, and egg production were monitored to 67 wk of age. In Experiment 2, pullets were moved at 19 wk of age and subjected to 14L:10D or 17L:7D light programs. Production parameters were measured as previously described. No significant (P greater than 0.5) interactions were observed between rearing and laying photoperiods, suggesting that increase in the length of photoperiod around time of maturity is not essential for adequate performance. In Experiment 1, ahemeral lighting resulting in reduced egg production, whereas egg shell quality and egg weight were improved (P less than .05). In both experiments, the 14-h rearing program resulted in improved egg size together with improved eggshell quality (P less than .05). Whereas increased egg size may relate to body weight, no explanation is apparent for the consistent pattern with respect to shell quality. In Experiment 2, poorer shell quality was observed with 17 vs. 14 h light per day. It is concluded that light stimulation at maturity has little effect on overall egg production. Improved shell quality observed with birds reared under 14 h light vs. those reared under 8 h per day may relate to a less rapid attainment of peak egg production.