by: Glenn Selk
Oklahoma State University, Emeritus Extension Animal Scientist

Fall calving season is just around the corner. In fact, the start of the fall calving season may be closer than many producers realize. Now is the time to get the calving kit ready and make certain that the calving shed is clean, in good operating condition, and ready for business.

Oklahoma State University physiologists studied early fall (August) and late fall (October) calving cows. 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.

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 degrees F for the “early” fall group. The average maximum temperature the week before parturition in the “late” calving group was 66 degrees F. There was a 100 percent survival rate for calves in both groups and both groups of cows had very high re-breeding rates (90 percent and 92 percent, respectively).

The average gestation length for the “early” cows was six days shorter (279 days) as compared to the “late” cows (285 days) in year 1. The average gestation length for the “early” cows was four days shorter (278 days) in year two. Producers with early fall-calving cows should expect calves to start coming several days ahead of the “textbook gestation table” dates. They should begin their routine heifer and cows checks at least a week to 10 days ahead of the expected first calving date.

Source: Kastner, Wettemann and co-workers. 2004 Oklahoma State University Animal Science Research Report.

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