Influence of photoperiod and prolactin on body composition and in vitro lipid metabolism in wether lambs.

An experiment was conducted to determine the possible effects of photoperiod and prolactin on the physical and chemical composition of body weight gain. Prolactin was manipulated by im injections of 2-Br-alpha-ergocryptine (CB154) or sc injections of ovine prolactin (oPRL) and by two light:dark regimens (16L:8D and 8L:16D). The four treatments employed were: 1) 16L:8D, placebo injections; 2) 16L:8D, CB154 injections; 3) 8L:16D, placebo injections and 4) 8L:16D, oPRL injections. After a 9-wk growth study, animals were slaughtered at similar body weights over the next 2-wk period. Weight of intestines was directly related and weight of pelt inversely related to circulating concentrations of prolactin. Content of N and lipid in the carcass was not influenced by treatment. However, N content of the noncarcass components was elevated (P less than .01) in animals receiving CB154. In vitro rates of acetate incorporation (nmol X 100 mg tissue-1 X 3 h-1) were higher in subcutaneous than in perirenal adipose tissue (1,920 vs 777; P less than .001). Rates for treatments 1, 2, 3 and 4 were 1,770, 953, 1,350, respectively. The rate for treatment 1 was greater than that for treatments 2 (P less than .001) and 3 (P less than .05). There was no stimulation of lipogenesis in response to insulin added to the incubation medium. In vitro rates of glycerol release (nmol X 100 mg tissue-1 X 2 h-1) were higher in perirenal than in subcutaneous adipose (135 vs 81; P less than .001). The respective treatment rates were 120, 84, 104 and 124, with treatment 1 being greater (P less than .05) than treatment 2. Epinephrine addition elevated glycerol release (156 vs 60; P less than .001). Differences for in vitro lipid metabolism between the perirenal and subcutaneous depots were independent of differences in cell size. Overall, these data indicate that the increased body weight gain due to extended lighting was not accompanied by detrimental effects on carcass composition. Nor was there any clear relationship between circulating concentrations of prolactin and in vitro lipid metabolism.