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Assessment of Thermal Status of Somatotropin-Injected Lactating Holstein Cows Maintained under Controlled-Laboratory Thermoneutral, Hot and Cold Environments^{1 ,2, 3,}

Wasmen Manalu⁴, Harold D. Johnson, Ru-Zhi Li^*, Barbara A. Becker^,5 and Robert J. Collier^**

Department of Animal Sciences U.S. Department of Agriculture, Agricultural Research Service, Animal Physiology Research Unit, University of Missouri, Columbia, MO 65211 ^* Department of Animal Production, Nanjing Agricultural University, Nanjing, People's Republic of China ^** Division of Animal Sciences, Monsanto Company, Chesterfield, MO 63198

Two experiments, with a single-reversal design and 12 cows per experiment, were conducted to study the effects of somatotropin on thermal status of lactating cows under laboratory thermoneutral (18 to 22°C, 30–50% relative humidity), hot (24–35°C, 30–50% relative humidity) and cold (-5 - +5°C, 50–55% relative humidity) conditions. Throughout the experiment six cows were injected with somatotropin (25 mg/d) and six with sodium bicarbonate. All injections were started the first day of the 30-d natural environmental period (22–35°C and 41–97% relative humidity for summer experiment, and -5 - +5°C and 4–25% relative humidity for winter experiment) before the cows were exposed alternatively to laboratory thermoneutral and hot or cold environments. The somatotropin-treated cows had higher energy intake (13 and 17%), heat production (19 and 25%), heat loss (36 and 24%) and milk energy (40 and 49%), than control cows under thermoneutral and hot conditions, respectively. The somatotropin-treated cows had higher heat production (18 and 10%), respiratory heat loss (27 and 17%) and milk energy (14 and 25%) than control cows under thermoneutral and cold conditions, respectively. The increased heat production associated with somatotropin was accompanied by increased heat losses. Part of the increased heat production was attributed to the increased milk energy and energy intake. These results suggest that increased heat production during somatotropin treatment was within the range that could be dissipated by the cows.

KEY WORDS: • bovine somatotropin • thermal stress • heat production • heat loss • cows

¹ Contribution from Missouri Agricultural Experiment Station. Journal Series Number 11,347.

² Presented in part at the 82nd Annual Meeting of the American Dairy Science Association, June 1988, at the University of Alberta, Edmonton, Canada [Manalu, W., Johnson, H. D., Becker, B. A., Li, R., Abdalla, E. B., Katti, P. S. & Collier, R. J. (1988) Effects of sometribove (methionyl bovine somatotropin, BST) on heat balance during heat and cold exposure in lactating cattle. J. Dairy Sci. 71(Suppl. 1):124(abs. P17)] and in International Symposium Washington: Biotechnology for Control of Growth and Product Quality in Meat Production, Implications and Acceptability, Dec. 5–7, 1990, Rockville, MD [Becker, B. A., Johnson, H. D., Knight, C. D., Collier, R. J., Manalu, W. & Baile, C. A. (1990) Effect of exogenous somatotropins on thermal balance and consequences in thermally stressful environments. Paper #9].

³ Mention of a trade mark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.

⁴ Permanent address: Department of Physiology and Pharmacology, Faculty of Veterinary Medicine, Bogor Agricultural University, Jalan Taman Kencana No. 1, Bogor, Indonesia.

⁵ To whom correspondence should be addressed.

Manuscript received 10 January 1991. Revision accepted 22 May 1991.

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