The effects of dietary restriction during the growth period on rate of growth, mature body weight, tissue proportions, and adipose tissue cellularity of broiler-type chickens

Male and female broiler-type chicks were subjected to different periods of dietary restriction between the ages of 0 and 14 weeks of age. Feed was restricted during this period of time by limiting feed consumption to 30 minutes of feeding per day. Growth rate of the birds and mature body weights were measured. The proportion of organs and tissues, and adipocyte diameter and number in the retroperitoneal and M. sartorius depots were determined in mature female birds subjected to the different periods of dietary restriction. The following summarizes the findings: 1. Male and female birds subjected to different periods of dietary restriction from 0-14 weeks of age had similar body weights at the end of any given period of feed restriction. However, following ad libitum feeding, the male birds previously subjected to different periods of dietary restrictions, grew at a greater rate and obtained a greater final body weight than did the females. 2. Dietary restriction increased mortality in both male and female birds. There was, however, no sex difference in mortality in response to the early dietary restriction. Cropbound birds and birds with leg weakness accounted for most of the mortality. Dietary restriction from 0-12 and from 0-14 weeks of age caused significant decreases in the mature body weights of female birds. The lighter weights appeared to be due to a reduction in the growth of all tissues since the proportional -weights of the M. pectoralis major, liver, tibiotarsus, retroperitoneal and M. sartorius adipose depots were similar in the restricted and the control birds. The tibiotarsus and the M. sartorius adipose depot were the tissues most sensitive to the dietary restriction. Since the weight of the retroperitoneal adipose depot was not significantly affected by dietary restriction, there may be differences in the responses of the retroperitoneal depot and the M. sartorius depot, to early dietary restriction. Determining the average, retroperitoneal adipocyte diameter at 17-19 weeks and 40-43 weeks of age, revealed that adipocyte enlargement in the retroperitoneal depot occurred in all treatments between the) two ages. Adipocytes from the retroperitoneal depot were significantly larger than adipocytes from the M. sartorius depot regardless of dietary treatment. Dietary restriction reduced the average adipocyte diameter in the retroperitoneal and the M. sartorius depots of birds subjected to dietary restriction from 0-12 and from 0-14 weeks of^age; and the effect on cell size was still apparent at 40-43 weeks of age. 7. Adipocyte cellularity in the M. sartorius depot was similar for all treatments studied, indicating that the number of adipocytes in this depot was unaffected by early dietary restriction. In the retroperitoneal depot, however, birds restricted from 0-12 and from 0-14 weeks of age had significantly more adipocytes than did the control birds. Whether this increase in observable adipocytes reflected an increase in adipocyte cellularity or an increase in the lipid-filling of pre-adipocytes is not clear from this study The difference in response to early dietary restriction exhibited by the retroperitoneal and the M. sartorius depots may reflect a greater propensity of adipocytes in the retroperitoneal depot to multiply.Land and Food Systems, Faculty ofGraduat