EFFECTS OF DIETARY FAT AND BODY WEIGHT ON PROTEIN AND ENERGY UTILIZATION IN LAYING HENS.

Abstract

Four experiments were carried out with laying hens to evaluate the effects of body weight, age, dietary protein, and tallow levels on performance, nutrient intake and energy utilization. In the first experiment, Single Comb White Leghorn birds were divided into four body weight groups at the onset of egg production. Voluntary feed intake was 18% less for the lightest (1.39 kg) in comparison with the heaviest group (1.83 kg). Egg weight was directly related to body weight with the heavy birds producing an average egg weighing 65.3 g and the lightest birds having an average egg weight of 58.9 g. Feed conversion was also significantly better for the lighter birds. Maintenance requirements for the heaviest and lightest birds were 60.5 and 57.9% of metabolizable energy consumed, respectively. Metabolizable energy intakes above maintenance were 131 kcal/d for the heavy birds and only 119 kcal for the light group. A composite regression analysis indicated a maintenance requirement of 127.7 kcal/d/kg('0(.)75) and an energetic efficiency of 75.2% for the conversion of metabolizable energy to net energy. In order to evaluate the effects of age and body weight on laying hen performance, the last three experiments were designed using old, molted, and young hens which were divided into the heaviest and lightest body weight groups. The old birds were 72 weeks old, the molted birds were 106 weeks old, and the young birds were 27 weeks old at the start of the studies. In each experiment the birds were fed ten experimental diets with 12, 14, 16, 18, and 20% dietary protein in combination of 1 and 4% supplemental fat. Egg output was increased with the supplementation of tallow in only the young birds; while energy retentions were improved in the old and molted birds with fat feeding. Average energy retentions per kg physiological body weight were 58.8, 41.7, and 38.6 kcal for the young, molted, and old hens, respectively. The light-bodied birds showed 9% better gross energetic efficiencies than the heavy-bodied birds. Estimated daily protein intake requirements were 16.8, 13.3, and 12.8 g/d to support production levels of 84, 64, and 66% for the young, old, and molted birds, respectively.