Dietary Energy and Fat Content as Factors in the Nutrition of Developing Egg Strain Pullets and Young Hens

Four hundred commercial S.C.W.L. chicks of two strains were floor 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. At 18 weeks of age the pullets were moved to a windowless cage house, housed in individual cages, fed two laying diets that differed in energy and fat content and sacrificed after 280 days of lay. Moisture, fat, nitrogen and ash were determined on each carcass and liver. While feeding of the high energy rearing diet depressed feed intake (approximately 7% over the duration of the rearing period) and resulted in a marked increase in caloric intake from 6 to 18 weeks of age, energy level of the rearing diet failed (P=0.05) to affect mortality or body weight gains. Energy level of the rearing diet failed (P=0.05) to affect subsequent mortality, production (hen day basis), efficiency (g. feed/egg) or body composition at the end of lay. Energy content of the laying diet significantly (P=0.05) depressed feed intake and significantly (P=0.05) increased caloric intake, body weight gains, efficiency (g. feed/egg), abdominal fat pad weight (g.) and total body fat. While many strain differences were noted in the various parameters studied, of considerable importance was the finding of no significant strain by diet energy level interaction. This finding suggests that, while significant strain differences may occur, the two strains responded in a similar manner to changes in the dietary energy content of the laying ration. Body and liver composition for the two strains did not differ at the end of lay.