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Effect of Bovine Growth Hormone Administration on Metabolism of Growing Hereford Heifers: Dietary Digestibility, Energy and Nitrogen Balance^1,2,

Department of Animal Science, Cornell University, Ithaca, NY 14853 ^* Ruminant and Nonruminant Nutrition Laboratories, U.S. Department of Agriculture, Agricultural Research Service, Beltsville, MD 20705

The objective was to determine the effect of daily s.c. injection of bovine growth hormone (bGH) on nitrogen and energy balance in six Hereford heifers. In addition, effects on urinary excretion of 3-methylhistidine and hydroxyproline and on serum mineral concentrations were monitored. A single reversal design was used with two 14-d injection periods of placebo or bGH (29.2 IU/d). Measurements were made on d 8–14 of each period. Injection of bGH did not alter apparent digestibility of dry matter, energy or nitrogen, nor urinary excretion of 3-methylhistidine or hydroxyproline. Serum concentrations of calcium, phosphorus and magnesium were normal with bGH treatment. Nitrogen retention was higher and urinary nitrogen excretion was lower when the heifers were injected with bGH than with the placebo demonstrating an effect of bGH on postabsorptive metabolism of nitrogen. Total energy balance was not altered by treatment. Energy retained as protein was higher after bGH treatment than after the placebo, implying decreased energy retained as fat and demonstrating a role for GH in altering energy partition in growing animals. Total heat production was not altered by treatment indicating no change in the gross efficiency of metabolizable energy use with bGH treatment.

KEY WORDS: • growth hormone • cattle • energy balance • nitrogen balance

¹ Supported in part by U.S. Department of Agriculture Cooperative Agreement No. 58-32U4-3-453, The Upjohn Company, American Cyanamid Company and Monsanto Industrial Chemicals Company.

² Presented in part at the 76th Annual Meeting of the American Society of Animal Science, August 1984, University of Missouri, Columbia, MO. Abstract published in J. Anim. Sci. 59 (Suppl. 1), 202, 1984.

³ Present address: U.S. Department of Agriculture, Agricultural Research Service, Roman L. Hruska U.S. Meat Animal Research Center, Clay Center, NE 68933. To whom reprint requests should be addressed.

⁴ Present address: USDA, Subtropical Agricultural Research Station, Brooksville, FL 33512.

⁵ Deceased.

Manuscript received 14 May 1985. Revision accepted 24 September 1985.