Dietary Energy and Fat Content as Factors in the Nutrition of Developing Egg Strain Pullets and Young Hens: 1. Effect on Several Parameters and Body Composition at Sexual Maturity

Abstract

Four hundred commercial S.C.W.L. chicks of two strains were cage reared on two dietary programmes (pullet versus broiler diets) which differed in energy content by approximately 457 kcal. of M.E./kg. for the starting and growing diets. Upon reaching sexual maturity (age at first egg) the pullets were killed and a number of parameters measured. Moisture, fat, nitrogen and ash were determined on each carcass and liver.Pullets receiving the high energy diets consumed 19% less feed, significantly more protein (9.2 versus 8.7 g./day) and approximately the same calories (139 versus 143 kcal. M.E./day) to 18 weeks of age, as did pullets receiving the low energy diet. No difference in body weight was evident.Energy level of the diet had no effect at sexual maturity on the following parameters; mortality, age, body weight, wet liver weight, liver color or liver firmness, liver water, fat, protein or ash, abdominal fat pad weight, total body water, fat, or ash. The carcasses of pullets receiving the high energy diets contained significantly more protein.Significant strain differences were apparent for many of the parameters studied. The heavy bodied pullets (Strain B) showed less mortality, consumed more feed, energy and protein to 18 weeks of age and gained more weight. The heavy bodied pullets reached sexual maturity 6.3 days earlier and weighed 168 grams more than the light bodied strain. Abdominal fat pad and liver weights were heavier at sexual maturity for Strain B birds. Livers from Strain B birds showed a lighter color score. The heavy bodied birds contained 2.21% less water, 2.7% more fat and 0.43% less protein than the light bodied pullets. Total body ash and liver composition were unaffected by strain.Regression equations to predict total body fat and protein from total body water were developed.