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Influences of Age, Breed and Sex on Plasma Hormones in Cattle¹

Iowa State University of Science and Technology, Ames³ 50010

Abstract

Blood samples were obtained from Angus, Hereford, Shorthorn and crossbred cattle when 18 (116 animals), 204 (129 animals) and 371 (89 animals) days old. No differences in plasma levels of growth hormone, insulin or protein-bound iodine could be related to age or breed of the animals. The male compared with female cattle had slightly higher plasma levels (17.4 vs. 12.9 ng/ml) of growth hormone. At 371 days, when the steers were fed a finishing ration and the heifers were fed a lower energy ration, the males had higher levels (41.4 vs. 19.7 µU/ml) of plasma insulin. The results of this study indicated there was no marked dilution of plasma hormones with increasing age of cattle.

¹ Journal Paper No. J-6547 of the Iowa Agriculture and Home Economics Experiment Station, Ames. Project No. 1208. This work was supported in part by the Iowa State University Research Foundation.

² Present address: Extension Production Livestock Specialist, 310 Kahl Building, 326 West Third Street, Davenport, Iowa 52801.

³ Department of Animal Science.