Producers with cows set for fall calving should start thinking about their plan and get the calving kit ready, according to Glenn Selk, Oklahoma State University Cooperative Extension emeritus cattle specialist.
"Producers with early fall-calving cows should expect calves to start coming several days ahead of the textbook gestation table dates," he said. "They should begin routine cow checks at least a week to 10 days ahead of the expected first calving date."
Selk's advisory is based on a 2004 OSU livestock physiologists' study of early fall (August) and late fall (October) calving cows, which looked at gestation length, weather and survival rates.
Data from two successive years were combined for 50 Angus x Hereford crossbred cows. The early and late fall calving cows had been artificially inseminated in early November or early January respectively.
"Semen from the same sire was used for all cows," Selk said. "All cows were exposed to a single cleanup bull for 35 days at four days after the artificial insemination 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 degrees F for the early fall group vs. 66 degrees F for the late fall group.
"There was a 100% survival rate for calves in both groups and both groups of cows had very high rebreeding rates of 90% and 92% respectively," Selk said.
The average gestation length for the early cows was six days shorter – 279 days – compared to the late cows – 285 days – in the first year of the study.
In the second year, the average gestation length for the early cows was four days shorter – 278 days – compared to the "late" cows at 282 days.