Peripheral testosterone in boars after administration of hCG, ACTH and testosterone at three ages

The frequency of short cycles after the first postpartum estrus was determined from data collected in three experiments. Short estrous cycles (SEC) were defined as those less than 17 days long. Cows that were bred at the first estrus postpartum and conceived were included in the non-short cycle count. In Exp. 1, designed to determine the influence of genetic ability for milk production on postpartum traits, 16 of 118 Holstein cows (13.6%) had short estrous cycles. The incidence of SEC was greater in the low milk production group, but the differences were not significant (P>.25). This group had a shorter mean postpartum interval to first estrus (PPI) when compared to the high milk production cows (P<.025). Exp. 2 was designed to test the influence of suckling versus nonsuckling on postpartum traits, and seven of 54 Angus cows (13.0%) had SEC. The incidence of SEC in suckled and nonsuckled cows was 2 26 and 5 28 , respectively (P<.25). The nonsuckled cows had a shorter (P<.005) PPI than suckled cows. When these cows were grouped according to winter or summer calving, the incidence of SEC was 1 20 vs 6 34 (P<.25). In Exp. 3, designed to determine breed of sire x nutrition interactions on postpartum traits, there were 14 SEC out of 174 (8.0%) first estrous cycles in three parities of 58 crossbred cows. There was a tendency (P<.15) for more SEC to occur in the high nutrition group, but this may have been due in part to two cows in the high nutrition group that exhibited SEC in more than one parity. The high nutrition group also tended (P<.10) to have a shorter mean PPI than the low nutrition group. In all experiments, there were more SEC among cows displaying first estrus before 20 days postpartum.