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.