Influence of Nutrient Density on Growth and Carcass Composition of Weight-Segregated Leghorn Pullets

Abstract

Leghorn pullets were weight-segregated at either 8, 12, or 16 weeks of age and classified as either light, medium, or heavy weight. Six replicate cages each containing 10 birds of each of the three weight groups received a control diet ad libitum that contained 15% CP and provided 2800 kcal ME/kg. The same replicate number of light-weight pullets were also offered either high protein (18% CP, 2800 kcal ME/kg) or low energy (15% CP, 2400 kcal ME/kg) diets. Groups of heavy pullets received either low protein (12% CP, 2810 kcal/kg) or high energy (15% CP, 3200 kcal/kg) diets. Feed intake and body weight were recorded at 12, 16, and 19 weeks of age. At 19 weeks of age, 12 birds per treatment were sacrificed for carcass analysis.Diet modification had no beneficial effect on stimulating the growth rate of light pullets regardless of age. High protein diets increased protein intake of the light pullets (P<.05), although this was not related to growth or carcass composition. Feeding light pullets a low energy diet resulted in reduced energy intake (P<.05), contrary to the situation previously reported with unsegregated pullets. Feeding a high energy diet to the heavy pullets resulted in increased energy intake (P<.05) with no moderating effect on growth rate. Growth rate of the heavy pullets was tempered through use of low protein diets introduced at 8 or 16 weeks of age. Feeding the high energy diet to heavy pullets resulted in a consistent trend for increased carcass fat content. A possible explanation for these results is that genotype is largely responsible for early differences in body weight. (

Response of Leghorn Pullets to Protein and Energy in the Diet when Reared in Regular or Hot-Cyclic Environments

“…With pullets identified as being small at 12 wk of age, these same authors show little differential response of birds to diets of 3,100 kcal ME/kg and 20% CP vs. diets of 2,700 kcal/kg and 14% CP. The above results are similar to those reported by Leeson and Summers (1984b), where genetically small pullets in a population failed to respond to dietary manipulation. Another factor that may confound experiments involved with the use of high energy diets is inadequacy of protein or amino acid intake.…”

“…Feed intake per cage group was also ascertained over these time periods. Shank length was measured when birds were 28, 36, and 84 days of age (Leeson and Summers, 1984b).…”

Effects of Metabolizable Energy Intake and Body-Weight Restriction on Layer Pullets: 1-Growth, Uniformity, and Efficiency

“…Dietary energy dynamics in animals are complex depending on the dietary nutrients provided, and several reviews have shown their complexity in depth [20][21][22]. Ultimately, changes in dietary energy can enhance or reduce pullet growth rate and modify the growth of fat tissue, muscles and the relationship between fat and lean deposition [23,24].…”