Reproductive
physiologist Tom Geary prepares to take a blood sample from a cow to measure
her hormones. An ultrasound monitor on the right indicates this cow is 45 days
pregnant. Click the image for more information about it.
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Fertility Study Looks at Ovulation's Intricate
Workings
By Erin
Peabody May 31, 2005
Agricultural Research Service (ARS) scientists are getting ever closer to
finding out what makes animals tick reproductively. In efforts to boost
fertility in beef cattle, researchers have discovered that the folliclea
tiny structure within a cow's ovary that releases the eggmust reach full
maturity for pregnancy to have the best chance of success.
Pinpointing which hormonal cues enable the follicle to attain maturity
is still keeping the scientists busybut their findings are already
important for livestock producers who would like to artificially inseminate all
of their beef cows at the same time. The study could also shed light on issues
concerning human fertility.
Tom
Geary, a reproductive physiologist at ARS'
Fort
Keogh Livestock and Range Research Laboratory in Miles City, Mont., helped
conduct the studies, along with reproductive physiologist Michael Smith at the
University of Missouri-Columbia.
George Perry, a graduate student who worked with Geary and Smith
before joining the Animal and Range Science Department at
South Dakota State University in
Brookings, once theorized that follicle size might be the best indicator of a
cow's readiness to ovulate and establish a pregnancy.
But in a recent study, the researchers found that when cows were
allowed to naturally ovulate, it didn't matter what size their follicles
weretheir bodies intuitively knew when the tiny, blisterlike structures
were ready to release the eggs.
To induce ovulation in cows, beef producers administer the hormone
known as GnRH. As the study points out, if the hormone is injected before a
follicle is mature enough, pregnancy has a lower chance of success.
Follicular cells may not be fully developed at the time of induced
ovulation because they're not producing enough estrogen, according to Geary. So
he and other Ft. Keogh researchers are currently looking to see if extra
estrogen helps coax follicle maturity along. This work could lead to higher
fertility rates in industry artificial insemination programs.
The researchers' studies relating to follicle maturity were published
recently in the Proceedings of the National
Academy of Sciences.
ARS is the chief scientific research agency of the
U.S. Department of Agriculture.