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Effect of Feeding, Fasting and Infusion of Energy Substrates on Plasma Growth Hormone Levels in Cattle¹

Iowa State University of Science and Technology, Ames 50010

Abstract

The mean plasma growth hormone levels in four 5-month-old heifers were 12.8 Ng/ml before feeding, 11.0 Ng/ml during the 6-hr, period after feeding and 10.6 Ng/ml 46 to 58 hr. after feeding. No evidence was obtained to indicate that fasting alone was a stimulus to growth hormone secretion in cattle. Infusion of acetate, propionate or butyrate did not alter plasma levels of growth hormone. Inhibition of glucose metabolism with 2-deoxy-glucose did not change plasma levels of the hormone. A greater growth hormone secretory response to infusion of arginine occurred in fasted heifers as compared with fed heifers. Repeated measurement of plasma growth hormone levels during two 12-hr, periods in four heifers indicated that there was considerable variation in plasma levels within animals that were not related to changes in plasma glucose or the environment.

¹ Journal Paper No. J-6764 of the Iowa Agriculture and Home Economics Experiment Station, Ames. Project No. 1790. This work was supported in part by the Iowa State University Research Foundation.

² Department of Animal Science.