Effects of Controlled Heat Stress on Ovarian Function of Dairy Cattle. 1. Lactating Cows

The objective of this experiment was to determine the effects of controlled heat stress on ovarian function of lactating dairy cows. Estrus was synchronized (estrus = d 0), and cows were randomly assigned to either heat stress (n = 11; 29 degrees C, 60% relative humidity) or thermoneutral (n = 11; 1...

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Published in:Journal of dairy science 1998-08, Vol.81 (8), p.2124-2131
Main Authors: Wilson, S. J, Marion, R. S, Spain, J. N, Spiers, D. E, Keisler, D. H, LUCY, M. C
Format: Article
Language:English
Subjects:
Animals
Biological and medical sciences
Body Temperature
Cattle - physiology
Corpus Luteum - physiology
Eating
Estradiol - blood
Estrus
Estrus Synchronization
Female
Fundamental and applied biological sciences. Psychology
Hormone metabolism and regulation
Hot Temperature
Humidity
Lactation - physiology
Luteolysis
Mammalian female genital system
Ovarian Follicle - physiology
Ovary - physiology
Progesterone - blood
Vertebrates: reproduction
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Summary:The objective of this experiment was to determine the effects of controlled heat stress on ovarian function of lactating dairy cows. Estrus was synchronized (estrus = d 0), and cows were randomly assigned to either heat stress (n = 11; 29 degrees C, 60% relative humidity) or thermoneutral (n = 11; 19 degrees C, 60% relative humidity) treatment. For cows undergoing heat stress, ambient temperature (19 degrees C) was increased from d 11 to 13 of the estrous cycle (3.3 degrees C/d increase) and remained at 29 degrees C until d 21. Beginning on d 11, the growth and regression of ovarian follicles and corpora lutea were measured by using ultrasonography. Blood was collected daily by coccygeal venipuncture for measurement of serum concentrations of progesterone and estradiol. The second wave dominant follicle was more likely to ovulate in cows in the thermoneutral treatment than in cows undergoing heat stress (91 vs. 18% ovulation, respectively). Patterns of follicular growth in cows under-going heat stress were associated with decreased serum estradiol from d 11 to 21 and on the day of luteolysis. The average day of luteolysis was delayed by 9 d in heat-stressed cows. Conclusions were that follicular growth and development and luteolytic mechanisms were compromised in heat-stressed cows; as a result, luteolysis was delayed, and second wave dominant follicles did not ovulate.
ISSN:0022-0302
1525-3198
DOI:10.3168/jds.s0022-0302(98)75788-1