Magazine article Science News

Follicle Size Matters: Hormone Regimen May Reduce Pregnancy Success

Magazine article Science News

Follicle Size Matters: Hormone Regimen May Reduce Pregnancy Success

Article excerpt

The hormone injections used to induce livestock and women to ovulate may force some eggs to leave ovarian follicles too early to begin and maintain a successful pregnancy, a new study reports. This finding, made in beef cattle, may explain why women who receive this type of fertility treatment have lower pregnancy and birth rates than do women who ovulate on their own.

For convenience, livestock breeders like to artificially inseminate all their cows or the same day. To do this, they frequently provide a standard series of hormone shot, starting 9 days before insemination that induce entire herds to grow follicles and release eggs simultaneously.

Although the treatment is identical, each cow's follicles may grow at a different rate and thus end up being different sizes at ovulation. George A. Perry of the University o Missouri in Columbia and his colleagues wondered whether this variation in follicle size affects whether cows can establish or maintain pregnancies.

Perry's team started by studying a herd in which all the cows were artificially induced to ovulate. The researchers tracked hormone concentrations in the animals blood from the first injection until insemination and did daily ultrasound scans to measure ovarian follicles.

They found that cows with follicles of 11 millimeters or smaller across at ovulation were significantly less likely to become pregnant than cows with larger follicle were. All cows that lost pregnancies, about 13 percent of the herd, had had the smaller follicles at ovulation. …

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