Abstract
A major objective of this study was to determine if early postpartum breeding of dairy cows is detrimental to the animals' future reproductive performance. A total of 393 calving intervals of 168 Holstein cows was used in an experiment of factorial design to compare the effects of breeding at the first postpartum estrus with the effects of breeding at the first postpartum estrus after 74 days, and how these effects might be modified by two different levels of nutrition and two genetic levels for milk production. The first postpartum ovulation occurred without observed estrous behavior in 43% of all calving intervals and high nutrition increased the percentage compared to average nutrition. The interval to first postpartum estrus was longer for cows with high genetic potential for milk production than for genetically low producers and longer for cows on high nutrition compared to average nutrition. Fertility at first insemination was lower in cows bred at the first estrus following calving compared to those bred at a later estrus. There was no indication that early breeding had a cumulative detrimental effect on fertility. The average fertility at second, third and fourth inseminations was similar for the two breeding groups. The first-estrus breeding group had fewer “open” days than the later-estrus breeding group but required more inseminations per pregnancy. Cows on high nutrition had more retained placentas than those on average nutrition and similarly had a higher incidence of metritis. Genetically high-producing cows also had more retained placentas than low producers. Significant differences were not found for the occurrence of lost pregnancies, abortions, twinning, dystocias and nonbreeders. Early breeding can be used to shorten the calving interval thereby increasing reproductive efficiency. The percent fertility at first inseminations will be lower than for later breedings. Copyright © 1974. American Society of Animal Science. Copyright 1974 by American Society of Animal Science.