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Effects of Breed and Zeranol Implantation on Serum Insulin, Somatomedin-Like Activity and Fibroblast Proliferative Activity¹

The Pennsylvania State University, University Park 16802

Abstract

Twenty-eight Suffolk-sired (Sx) and 28 Finnsheep-sired (Fx) lambs were implanted with either 0 or 12 mg zeranol. Zeranol significantly increased average daily gain over that of controls. Serum taken at biweekly intervals for 6 weeks was assayed for insulin, somatomedin-like activity (Sm) and fibroblast proliferative activity (FPA). Insulin appeared to increase with time, but there were no consistent time changes for FPA or Sm. Serum insulin concentration was higher (P<.05) in implanted lambs than in controls (33.4 vs 25.6 µU/ml). Unlike insulin, serum Sm and FPA were not affected by zeranol implantation, and, thus, these serum factors appeared not to be involved in zeranol-stimulated growth. Sm was higher in the faster growing Sx lambs than in the slower growing Fx lambs. Thus, serum Sm activity may be involved in normal regulation of growth

¹ Authorized for publication as Paper No. 5751 in the Journal Ser. of the Pennsylvania Agr. Exp. Sta.

² Dept. of Dairy and Anim. Sci.

³ Present address: Upjohn and Co., Kalamazoo, Ml 49001.

⁴ Present address: Dept. of Foods and Nutrition, Univ. of Georgia, Athens 30602.