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  Discussion on Research Study: Stress and Embryo Recovery Rates
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DrO

Posted on Tuesday, Feb 24, 2009 - 10:02 am:

It has always made sense that stress during reproduction should lower reproductive efficiency. However studies have looked at the stress of transportation on pregnancy immediately following breeding and did not find an effect. Here a relatively small study found a remarkable reduction in embryos recovered when mares were exercised while it was hot and humid during the first 7 days post breeding. Though the percent reduction remarkable the small population suggests this needs conformation and perhaps a better definition of what is acceptable through further experimentation. It should serve as a common sense warning to keep those bred mares stress free.
DrO


Anim Reprod Sci. 2009 Feb;110(3-4):237-44. Epub 2008 Jan 20.
Embryo recovery from exercised mares.

Mortensen CJ, Choi YH, Hinrichs K, Ing NH, Kraemer DC, Vogelsang SG, Vogelsang MM.

Department of Animal Science, College of Agriculture and Life Sciences, Texas A&M University, College Station, TX 77843-2471, USA. cmorten@clemson.edu

The effect of exercise on mare reproductive efficiency was evaluated by comparing rates of embryo recovery from mares assigned to either an exercise regimen or a non-exercise (control) regimen. Exercised mares were worked daily for 30 min under average ambient conditions of >30 degrees C and >50% humidity. Mares were inseminated during estrus and subjected to uterine flush for embryo recovery on d 7 after ovulation for two consecutive cycles. After this, mares were allocated to the opposite group and allowed an estrous cycle without reproductive manipulation; then insemination and uterine flushing were conducted on two more consecutive cycles. Prostaglandin F(2alpha) was administered on the day of uterine flush. Mare rectal temperature increased during exercise from a mean of 38 degrees C to a mean of 39.9 degrees C. Mares had ovulations from smaller follicles when exercised than they did under control conditions (39.8+/-0.5 compared with 41.5+/-0.5mm diameter; P<0.05), and had an increased time from PGF(2alpha) administration to subsequent ovulation (8.47+/-0.337 compared with 9.27+/-0.294 d; P<0.05). Embryo recovery from control mares was 22 of 35 (63%). Fewer embryos were recovered from exercised mares (11 of 32, 34%; P<0.05). The proportion of embryos classified as Grade 1 tended to be less in exercised than in non-exercised mares (4 of 11, 36% compared with 16 of 22, 73%; P=0.051). These data indicate that exercising mares in a hot and humid environment are associated with changes in ovarian follicle development and ovulation, and a reduction in embryo recovery.
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