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Improve pregnancy rates with simple adjustments

Tweaking general management of the beef herd can improve breeding-season success.

“Accurate detection of estrus, inseminator efficiency, and fertility of the semen are all vital to the success of any breeding program,” says George Perry, South Dakota State University Extension beef reproductive management specialist. “However, even when these three elements are well managed, other factors can reduce pregnancy rates.”

Management in early stages of pregnancy
Management practices aimed at ensuring survival of embryos in the earliest stages of pregnancy (when they’re most vulnerable to death loss) can improve pregnancy rates.

At the time of insemination, fertilization rates can be as high as 89% to 100% when semen is present within the uterus at the time of ovulation. Early embryonic mortality is actually what causes the pregnancy rate to drop to 60% to 70%, the industry average for first-service conception rates.

“Nature contributes to much of this embryonic loss, but management practices can also increase mortality,” says Perry. “Stress can be detrimental to the embryos and can decrease pregnancy rates.”

When embryos are most vulnerable
Stress triggers changes in the uterus that can cause embryonic death. Embryos are most vulnerable between days five and 42 after insemination. Research has shown that shipping cattle during this critical window can result in a 10% drop in pregnancy rates.

After day 42, the embryo is increasingly less vulnerable. Yet, stress-induced embryonic death is still possible. Research suggests that shipping cattle 45 to 60 days after insemination can result in a 6% loss in embryos.

If breeding heifers involves relocating them by trailer, Perry recommends hauling them 30 days before the start of breeding season.

“With older cows, this is not such a big deal,” he says.

Heat stress
While difficult to manage, heat stress, too, can cause embryonic death. An increase in rectal temperature of 2˚F. or 3˚F. on the day of insemination can compromise the development of the embryo. Heat stress can impact pregnancy rates from 42 days before breeding and for as long as 40 days after breeding.

Nutrition and energy
Managing cattle so adequate nutrition is maintained before and after the breeding season is another way to improve pregnancy rates. In order to sustain a normal estrous cycle, females should be on an increasing plane of nutrition prior to breeding.

“If a prebreeding plan requires moving heifers from feedlot to pasture, remember heifers will experience a negative energy balance during the adjustment period,” says Perry. “Moving them 30 days before the start of the breeding season gives them time to adjust. Mature cows adjust more quickly.”

Avoid decreasing nutrition after breeding, as well. Research shows that moving heifers from a wintering drylot to pasture immediately after AI’ing can increase early embryonic losses.

For best reproductive success, Perry suggests a body condition score of six for heifers at the start of the breeding season.

“For cows, a minimum score of five at calving gives them sufficient body reserves for lactation and initiates normal estrous cycles after calving,” he says.

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