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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