Excessive summertime heat can shorten gestation time for beef cattle

Research conducted by Oklahoma State University's Division of Agricultural Sciences and Natural Resources indicates that excessively hot summertime temperatures -- all too normal for the south-central region of the United States -- can shorten the gestation length of beef cows.

"Producers may need to adjust their herd management so as to help cows that require birthing assistance; OSU research shows that cows exposed to 90 degrees Fahrenheit or greater during the last two weeks of gestation calve an average of four days earlier than what is considered normal," said Bob Wettemann, OSU Regents professor and animal science researcher.

Wettemann added some calves in the OSU studies were born two weeks early in August, and showed good survival rates provided the newborn calves had access to sufficient shade.

"It's important that newborns be able to cool down and not be stressed," he said.

The OSU animal science studies strengthen consideration for cattle producers to use a fall-calving system with first-calf cows, instead of a spring-calving system.

"Lighter birth weights for fall-calving first-calf cows should decrease difficulties associated with small cows giving birth to large calves," Wettemann said.

In most mammals, the fetus determines when the birth will occur. There is essentially a "time clock" in the calf that determines when the process is going to be initiated. Recent scientific studies demonstrate that high temperatures can speed up the "time clock" during the last two weeks of gestation, because of hormonal changes in the cow and fetus.

"This is not automatically a bad thing as it can provide certain animal health benefits, but it does require earlier observation of cows during late gestation," Wettemann said. "When used in conjunction with selection of bulls whose genetics promote lower birth weights, producers potentially can see increased calf survival, and getting a live calf on the ground is the whole point."

Cattle and calves are the number one agricultural commodity produced in Oklahoma, accounting for 46 percent of total agricultural cash receipts and adding approximately $2 billion annually to the state economy, according to National Agricultural Statistics Service data.

NASS data indicates Oklahoma is the nation's fifth-largest producer of cattle and calves, with the third-largest number of cattle operations in a state.