Characteristics of Adipose Tissue Growth in Broiler-Type Chickens to 22 Weeks of Age and the Effects of Dietary Protein and Lipid

Abstract

Female broiler-type chickens were fed diets containing different concentrations of protein and fat in two experiments. The first experiment was for 4 weeks. The mean weights of the abdominal fat pads were inversely related to dietary concentrations of protein between 20 and 35%. Adipocyte size and cellularity of the fat pads were lower with 30 than 20% protein. Fat deposition in the abdominal pad was increased in 3-week-old chicks by isocaloric substitution of oil for starch in the diets. At 4 weeks of age the effect of oil was not significant with 30 or 20% dietary protein (no measurements were made in chicks fed 35 or 25% protein). In Experiment 2, the development of the abdominal fat pad in birds fed 18 to 33% protein was monitored for 22 weeks. By 7 weeks the distribution of adipocyte size was bimodal. The initial adipocyte population showed comparatively little increase in numbers after 12 weeks, but cell size continued to increase. The numbers of adippcytes in the second population of adipocytes was still increasing rapidly at 22 weeks, although the size of the cells in this population remained small. At 22 weeks the small cells constituted 62% of the total adipocyte population but contained only 2.4% of the lipid in the fat pad. Adipocyte cell size was significantly affected by dietary protein and energy until 9 weeks of age, but the effects subsequently declined.