Excessive summer heat can shorten the gestation time for beef cattle and trigger a greater incidence of premature births, according to research by Oklahoma State University's Division of Agricultural Sciences and Natural Resources.
“The 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," Bob Wettemann, OSU Regents professor and animal science researcher, told science website ScienceDaily.
Some calves in the OSU studies were born two weeks early, but showed good survival rates where the newborn calves had access to sufficient shade.
"It's important that newborns be able to cool down and not be stressed," Dr Wettemann said.
The OSU animal science studies, focused on northern hemisphere production systems, strengthen consideration for cattle producers to use an autumn-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," Dr Wettemann said.
In most mammals, the foetus 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 foetus.
"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," Dr 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."