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, American scientists have discovered.
They say this would also eliminate the need to detect when cows go into estrus, thus removing the main barrier to a more widespread adoption of artificial insemination in beef cows.
Animal reproductive physiologists Tom Geary, Michael F. Smith and George Perry discovered 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 that 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.
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A follicle appears like a blister on a cow’s ovary as it goes into estrus. Each contains an egg, along with cells that produce the estrogen that causes a cow to be in heat.
The follicle-size indicator only worked for cows that 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, one with 45 cows in 2001 and another with 273 cows in 2002. Ovulation was induced in all cows and produced similar results. In the larger study, miscarriages occurred only in cows that ovulated smaller follicles.
