Four experiments were conducted to compare adipocyte dynamics and body composition among adult chickens from lines differing in growth rate and feed consumption. In Experiment I, forced caloric overconsumption increased weight gain and fat deposition, with concomitant increases in the total adipocyte DNA content of the assayed fat depots. Injections of DNA-specific [methyl³H] thymidine resulted in higher radioactivity levels in the fat depots of forced versus ad libitum or restricted-fed birds. Evidently, stimulation of fat deposition in adult chickens can be associated with adipocyte hyperplasia. A second experiment was conducted to histologically examine the effects of forced caloric overconsumption on adipocyte size, number, and distribution in the retroperitoneal fat depot of adult weight-line birds. Similarly to Experiment I, force feeding increased fat deposition, resulting in increases in the retroperitoneal fat depot total adipocyte DNA content. The lipid/adipocyte DNA ratio also decreased during rapid depot expansion. This resulted in an increase in the small adipocyte population of the force fed birds when adipocyte diameter was increasing. Subsequently, when the constraints of force feeding were removed, adipose depot reduction occurred, with the mobilization of lipid from small as well as large adipocytes. In a third experiment, the effects of estrogen administration and partial lipectomy were examined. In addition to the weight-line birds, a commercial broiler breeder stock was utilized. Estrogen administration depressed body weight gain and abdominal fat deposition when compared to placebo implanted birds. Partial lipectomy depressed body weight, fat deposition, and abdominal fat total adipocyte DNA content. Lipectomy modified several components of carcass composition without altering feed intake. No indication of a compensatory hyperplastic response to lipectomy was indicated. A final experiment was conducted examining the effects of forced body weight fluctuations on body composition of male and females from the weight-selected lines. Although numerous first-order interactions were detected, force-feeding resulted in transient modifications in carcass composition and fat deposition which were more apparent in the high than low weight line, in females than males. After release to ad Iibitum feeding, the differences resulting from force feeding were reduced. / Ph. D. / incomplete_metadata