Effects of Somatotropin on Milk Yield and Physiological Responses During Summer Farm and Hot Laboratory Conditions

The effects of bST on performance and physiological responses of lactating cows was studied under farm summer and laboratory heat conditions. Twelve cows, 90 to 50 d postpartum, were injected with either bST or vehicle solution for 30 d under farm summer and 10 d under either laboratory thermoneutra...

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Bibliographic Details
Published in:Journal of dairy science 1991-04, Vol.74 (4), p.1250-1262
Main Authors: Johnson, H.D., Li, R., Manalu, W., Spencer-Johnson, K.J., Ann Becker, B., Collier, R.J., Baile, C.A.
Format: Article
Language:English
Subjects:
ambient temperature
Animals
Biological and medical sciences
blood composition
body temperature
Cattle - physiology
Circadian Rhythm
dairy cows
Drinking
Eating
feed conversion
feed intake
Female
Food industries
Fundamental and applied biological sciences. Psychology
Growth Hormone - pharmacology
heat production
heat stress
Hematocrit - veterinary
Hot Temperature
Humidity
Hydrocortisone - blood
Insulin - blood
Lactation - drug effects
Leukocyte Count - veterinary
Milk - secretion
Milk and cheese industries. Ice creams
milk fat percentage
milk protein percentage
milk yield
Prolactin - blood
Seasons
somatotropin
summer
Thyroxine - blood
Triiodothyronine - blood
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Summary:The effects of bST on performance and physiological responses of lactating cows was studied under farm summer and laboratory heat conditions. Twelve cows, 90 to 50 d postpartum, were injected with either bST or vehicle solution for 30 d under farm summer and 10 d under either laboratory thermoneutral or heat conditions. Somatotropin increased milk yield by 6.1 (21%), 8.1 (32%), and 7.3kg (35%) under the farm summer, laboratory thermoneutral, and heat conditions, respectively. Somatotropin also increased milk fat by 15 and 19% and dry matter intake by 16 and 18% under laboratory thermoneutral and heat conditions, respectively. Somatotropin increased the efficiency of feed conversion into milk without any significant changes in body weight and temperatures. Somatotropin reduced plasma concentrations of triiodothyronine and cortisol and had no effect on plasma prolactin and insulin concentrations. Somatotropin did not increase water intake; however, hematocrit was decreased. The results suggest that stimulatory effects of bST on milk production are still observed on heatstressed cows without any significant indications of additional heat stress.
ISSN:0022-0302
1525-3198
DOI:10.3168/jds.S0022-0302(91)78281-7