Gestation Intervals Shorter in Heat
Excessive summer heat may cause fall calves to be born
earlier than normal.
Cattle producers with fall-calving herds need to be aware that calves may be born earlier than normal this year because of the extremely hot summer experienced by the Southern Great Plains states.
"It's a good idea for producers to begin their routine heifer and cow checks at least a week to 10 days prior to the normally expected first-calving date," said Glenn Selk, Oklahoma State University (OSU) Cooperative Extension emeritus cattle specialist.
OSU animal science research studying cows calving in early fall (August) and late fall (October) indicates that calves may start coming several days ahead of "textbook gestation table" dates.
Data from two successive years were combined for 50 Angus ✕ Hereford crossbred cows. The "early" and "late" fall-calving cows had been artificially inseminated (AIed) in early November and early January, respectively. Semen from the same sire was used for all cows. All cows were exposed to a single cleanup bull for 35 days at four days after the AI season.
The weather prior to calving was significantly different for late pregnancy in the two groups. The average maximum temperature the week before calving was 93° F for the "early" fall group. The average maximum temperature the week before parturition in the "late" calving group was 66° F.
"There was a 100% survival rate for calves in both groups and both groups of cows had excellent rebreeding rates of 93% and 96%, respectively," Selk said.
The average gestation length for the "early" cows was six days shorter (279 days) as compared to the "late" cows (285 days) in year one. The average gestation length for the "early" cows was four days shorter (278 days) as compared to the "late" cows (282 days) in year two.
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