Search

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.

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 trials were undertaken to study the effect of nutrient intake on skeletal size in growing pullets. Leghorn chicks at 28 days were smaller in weight and shank and keel length when fed 16% as compared to 22% crude protein. Increasing the energy or mineral-vitamin concentration of the diet had no effect on skeletal parameters. Increased skeletal size of pullets in response to increased diet protein was associated with reduced (P less than .01) tibial ash content. In a subsequent trial, broiler breeder pullets were fed, ad libitum, starter diets (0 to 21 days) containing graded levels of protein from 20 to 13%. Reducing protein level had a consistent negative effect on body weight, shank length, and keel length at 21 days. When birds were subsequently fed restricted quantities of a common grower diet, no differences in body weight and skeletal parameters were evident at maturity. It is concluded that although early body weight and skeletal size can be markedly influenced by diet protein level, such effects are subsequently nullified by conventional restricted feeding programs.

Several experiments were undertaken to evaluate diets that could be used to bioassay methionine activity in various compounds. The following semipurified diets were tested: a corn-soy-gelatin basal (CSG) diet supplemented with essential amino acids (EAA) at 23% crude protein (CP); a soybean meal diet at 23% CP; and a soybean meal diet at 15% CP with all the protein coming from dehulled soybean meal and starch, glucose, and fat used as sources of energy. The CSG and 15% CP soybean meal diets proved to be sensitive in their response to methionine supplementation. Birds fed the CSG diet supplemented with methionine and tryptophan were smaller (P less than .01) than birds fed the 23% CP soybean meal diet, thus suggesting that something other than EAA was limiting the performance of birds fed this diet. Based on sensitivity to methionine supplementation, simplicity and cost of diet, the low protein soybean meal diet seems most appropriate for methionine bioassays.

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.

An experiment was conducted to examine the effect of previous diet on feed intake and weight gain, in the subsequent period, for broiler and Leghorn cockerels. Three dietary treatments, consisting of 20% protein and either 2400, 2800, or 3200 kcal Me/kg, were fed in combinations consisting of three, 2-week periods, with nine combinations in all. The experimental design was balanced for residual effects, and period weight gains and feed intake were determined. Analysis of the data by period indicated that treatments by residual interactions were confined to the final period. Therefore, it was concluded that diets fed in the previous two periods may be acting in combination to effect weight gain and feed intake in the final period. Examination of the pooled period data indicated that for optimum performance, broilers required a dietary regimen consisting of increased calorie-to-protein ratios with time while Leghorns required lower calorie-to-protein ratios. Type differences were also observed in the ability to adapt to high protein, low intakes: Leghorns grew optimally but body weight gain for broilers was reduced with such a feeding program.

Day-old male broiler chickens were fed diets containing 0, 5, 10, 15, or 20% raw, ground, full-fat canola for a period of three weeks. Increasing the dietary proportion of full-fat canola significantly reduced feed intake (P less than .05) and weight gain (P less than .01), without altering feed:gain ratio. Diet had no significant effect on protein retention although there was a significant decrease in fat retention with an increase in dietary levels of full-fat canola (P less than .01). This was accompanied by a significant decrease in metabolizable energy (P less than .01). Increasing the proportion of dietary full-fat canola significantly reduced the concentration of soap in the digesta (P less than .05) and excreta (P less than .01). There was no significant effect of the dietary treatments on calcium or phosphorus retention. There was also no effect of the dietary full-fat canola on bone ash, bone calcium, or phosphorus content.

Varying levels of dietary protein (16, 20, 24, 28, 32, 36%) and energy (2600, 2800, 3000, 3200, 3400, 3600 kcal [metabolizable energy] ME/kg) were fed in a factorial arrangement to broilers to determine the effect of alteration in nutrient density on performance and economic traits. Body weight and feed efficiency improved with increased dietary protein or energy. However, a significant interaction between protein and energy indicated the importance of a balanced energy: protein ratio to achieve optimum performance. Sex differences in protein requirements were observed for 49-day body weights. Returns over feed costs remained essentially constant, providing a balance between dietary protein and energy was maintained. However, an increase above 28% crude protein or 3400 kcal ME/kg resulted in reduced returns as did excessive quantities of one nutrient relative to the other. Male broilers were able to accommodate a higher level of dietary protein (24%) than female broilers (20%) before returns were reduced. Regression equations were derived for prediction of performance and economic parameters. Reliable estimates were obtained with the inclusion of protein or energy intake in addition to diet composition.

A number of experiments were undertaken using White Leghorn pullets to determine the effect of diet and growing treatment on 16-wk body weight and carcass composition. Irrespective of the level of dietary energy, body weight gain and carcass composition appeared to be closely correlated with energy intake of the pullets. Diets as low as 15% protein with and without methionine supplementation resulted in 16-wk body weights similar to those of animals fed diets containing 21% protein, suggesting that protein is not a critical nutrient influencing weight gain of pullets. Pullets fed ad libitum every other day from 12 to 16 wk of age were significantly lighter at 16 wk than pullets full fed a regular grower diet or the regular diet diluted with 20% oat hulls. Pullets must achieve a certain body weight and carcass composition in order to trigger the onset of production. Dietary energy, not protein, appears to be the critical nutrient involved.