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Agricultural Research Service

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Photo: Tom Geary prepares to take a blood sample from a cow to measure her hormones. Link to photo information
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Paving the Way for More Widespread Artificial Insemination of Beef Cows

By Don Comis
April 16, 2003

Procedures that cause cows' reproductive systems to have medium-sized, egg-containing follicles could ensure high pregnancy rates when artificial insemination is timed to synchronized ovulations, according to Agricultural Research Service scientists. This would also eliminate the need to detect when cows go into estrus ("heat"), thus removing the main barrier to a more widespread adoption of artificial insemination in beef cows.

Animal reproductive physiologists Tom Geary, with ARS in Miles City, Mont., and Michael F. Smith of the University of Missouri-Columbia, along with University of Missouri graduate student George Perry, learned that follicle size can be an important indicator for identifying less fertile cows, or cows that are prone to having miscarriages. The scientists found that cows which ovulate medium-sized follicles had the highest rate of successful pregnancies, about 70 percent. Those ovulating the smallest follicles had a successful pregnancy rate of only about 30 percent.

A follicle appears like a blister on a cow's ovary as she goes into estrus. Each contains an egg, along with cells that produce the estrogen that causes a cow be in heat.

The follicle-size indicator only worked for cows which were induced to ovulate at the time of artificial insemination. It could be that the most fertile cows grow medium-sized follicles, or it could be that certain ovulation-inducing techniques cause cows to grow medium-sized follicles that lead to higher fertility.

The follicle-size research should help scientists evaluate estrus and ovulation synchronization procedures before conducting large field trials.

The discovery came from two studies--the first with 45 cows in 2001, and the second study with 273 cows in 2002. Ovulation was induced in all cows and produced similar results. In the larger study, miscarriages occurred only in cows which ovulated smaller follicles.

More information about this research can be found in the April issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific research agency.

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