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Oregon State College
Abstract
The average interval from parturition to the first estrus was 59.2 days in 54 Angus cows and 62.7 days in 97 Hereford cows during a 3-year period. The line of breeding within the Hereford cows and breed dif- ference between the Angus and Hereford cows had no significant effect on the postpartum estrual interval. There was a highly significant effect of year on this interval. The age of cow at calving and sex of calf did not appear to influence the postpartum estrual interval.
The cow repeatability of this postpartum estrual interval was 0.06. There was a highly significant regression of –0.61 of the date of calving upon the interval from calving to the postpartum estrus. Therefore, a cow tended to have a shorter interval of 6.1 days for each 10 days that she calved later in the season. This phenomenon should contribute to a more uniform calving interval from one year to the next.
There was no significant effect of the interval from calving to breeding on fertility, although there was a gradual increase in fertility from the 11–30 day group to the 91–110 day group. The overall fertility following the first service was 74 percent. The fertility of cows bred for the first time at the first and second estrus irrespective of interval length was 72 and 78.3 percent, respectively.
1 Technical Paper No. 900, Oregon Agr. Exp. Sta., Animal Husbandry Dept., Corvallis.
2 Present address: Florida Agr. Exp. Sta., Gainesville.
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