Adipose tissue metabolism and its control in birds.

At any age, with increases in body weight, the elevation in total lipid or abdominal fat is more than proportional to body weight. This observation explains why selection of broilers for rapid growth rate leads to excessive fat accumulation. Although adipocyte hyperplasia continues until 12 or 14 weeks of age, hypertrophia becomes increasingly important with age and the degree of fattening. The number of adipocytes appears to be correlated with body size, and the size of the adipocyte is closely related to the fat content of the live bird. The hormonal control of lipolysis involves a number of hormones and appears to be very complex. The increase in fat in adipose tissue is mainly due to hepatic lipogenesis. This review discusses the relative role of hormones in fat metabolism, some pecularities of insulin activity in birds, and the important functions of plasma lipoprotein and adipose lipoprotein lipase. A comparison of a fat line of chickens and mammalian models of obesity is also made.