Glenn Selk Takes a Look at the Effects that Heat Stress Can Have on a Bull's Level of FertilityTue, 16 Jul 2019 10:11:04 CDT
Dr. Glenn Selk, Oklahoma State University Emeritus Extension Animal Scientist, offers herd health advice as part of the weekly series known as the "Cow Calf Corner" published electronically by Dr. Peel and Dr. Glenn Selk. Today, Dr. Selk discusses the impacts of hot weather on bull fertility.
"Last week’s newsletter contained a discussion of the impact of high pressure heat domes on cattle reproductive performance in the mid to late summer in Oklahoma. Now let’s look at the effect of heat stress on each side of the reproduction equation. First we examine the impact on the male. Next week we will look at research on the heat stressed cow.
"Several research trials have been conducted throughout the years looking at the effect of high temperatures on bull fertility. Certainly that research has importance to many Oklahoma and Southern Plains cattlemen in the summer of 2019.
"As far back as 1963, researchers exposed bulls to temperatures of 104 degrees F. and 54% humidity for an 8 period and then allowed the temperature to drop to 82 degrees F with 72% humidity for the remainder of the 24 hour period. This temperature regimen was continued for 7 days and was designed to resemble natural conditions in the subtropics. They found the high temperatures resulted in major detrimental effects on initial sperm motility, sperm concentration and total numbers of sperm per ejaculate. One cannot escape the conclusion that high ambient temperatures can result in detrimental effects on fertility by effects on both the cow and the bull.
"Oklahoma scientists (Meyerhoeffer, et al.1985, Jour. of Anim. Sci. 60:352) placed bulls in controlled environments of 95 degrees F. for 8 hours and 87 degrees for the remaining 16 hours while similar bulls were placed in environments of 73 degrees constantly. These treatments were applied to the bulls for 8 weeks and then all bulls were allowed to be in the 73 degree environment for another 8 weeks. During the treatment the heat stressed bulls had rectal temperatures of 101.7 degrees F and non-stressed bulls had rectal temperatures of 100.8 degrees F. The percentage of motile sperm cells decreased significantly in the stressed bulls by 2 weeks of heat stress. See the graph below. Sperm motility did NOT return to normal values until 8 weeks after the end of the heat stress. This explains some of the reduction in fertility that is often associated with summer and early fall breedings."
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