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Influence of Photoperiod and Prolactin on Body Composition and Vitro Lipid Metabolism in Wether Lambs^1,2,

Cornell University and US Department of Agriculture⁴, Ithaca, NY 14853-0281

³ Reprint requests should be sent to this author.

Abstract

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--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<.01) in animals receiving CB154. In vitro rates of acetate incorporation (nmol lOO mg tissue^–1 • •3 h^–1) were higher in subcutaneous than in perirenal adipose tissue (1,920 vs 777; P<.001). Rates for treatments 1, 2, 3 and 4 were 1,770, 953,1,320 and 1,350, respectively. The rate for treatment 1 was greater than that for treatments 2 (P<.001) and 3 (P<.05). There was no stimulation of lipogenesis in response to insulin added to the incubation medium. In vitro rates of glycerol release (nmol 100 mg tissue^–1 • 2 h^–l) were higher in perirenal than in subcutaneous adipose (135 vs 81; P<.001). The respective treatment rates were 120, 84, 104 and 124, with treatment 1 being greater (P<.05) than treatment 2. Epinephrine addition elevated glycerol release (156 vs 60; P<.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.

¹ The authors would like to express appreciation to the National Institute of Arthritis, Metabolism & Digestive Diseases and the National Pituitary Agency for providing the oPRL used in this study, and to Sandoz, Inc. for providing the CB154. Also M. L. Thonney, C. E. Allen and N. L. Firth are gratefully acknowledged.

² Supported in part by Cornell Univ. Agr. Exp. Sta., Merck Institute for Therapeutic Research and Agway, Inc.

⁴ Dept. of Anim. Sci.