Heat may trim calf crop next year

This summer's heat wave may have long-lasting effects on the Plains and Midwest beef herd, well beyond when the mercury's fallen.

A gathering of cattle producers and livestock specialists at a University of Missouri Extension field day earlier this month revealed a clear message: This summer's heat stress is likely going to manifest itself when next year's calving season arrives.

"I expect to get calls next spring from producers saying that their cows just quit calving," says University of Missouri Extension livestock specialist Zac Erwin, according to a university report.

That's mainly because of a 2-pronged danger posed by the heat wave: Bulls will "go bad" and cows can have trouble sustaining pregnancies until birth.

"We say that it's not the heat but the humidity. That was true this year, as high humidity makes it difficult for cows to cool down," Erwin says. "Also, high temperatures at night prevented cows from returning to a temperature-neutral zone."

Bulls have the toughest time when it's as hot as it's been in parts of the Plains and Midwest, Erwin adds. Even after the heat has abated, it can take a while for a bull to recover from heat stress.

"I often hear producers say when cows didn’t get bred, ‘The bull tested OK before the breeding season. This fall, he tests OK,’” Erwin says in a university report. “Problems can occur between those times. If a bull loses sperm quality, he takes 60 days to recover. That can cause a big gap in calving next spring.”

In general, it can take 10 to 20 days for a cow to recover reproductive capacity after a serious bout with heat stress.

A rule of thumb to avoid heat stress complications in your herd's reproductive capacity, Erwin says, is to limit summer breeding to those days when it's not as hot.

"Don't try to breed cows past July 1," he says. "That creates situations where cows won't get bred or can't maintain pregnancies."