Date of this Version
Livestock Science 148 (2012) 26–35; http://dx.doi.org/10.1016/j.livsci.2012.05.004
A study was conducted to determine if early weaning spring born calves can be an alternative management strategy during drought and if early weaning facilitates rebreeding of young cows. Our objectives were to determine effects of early weaning at the start of breeding on cow body weight, body condition score, and reproductive performance with or without estrous synchronization and AI in two herds in the Northern Great Plains, USA. In Exp.1and 2, crossbred cows were stratified within cow age by postpartum interval, and calf sex, and were assigned within strata to one of two weaning treatments at the start of breeding when calves averaged 80-d of age: (1) early weaned (permanent calf removal); or (2) no weaning (calves suckled cows until normal weaning approximately 210-d of age). Cows in Exp.1 were exposed to natural service whereas cows in Exp.2 were exposed to estrous synchronization for AI using a CIDR for 7 d with GnRH at CIDR insertion and PGF2α at CIDR removal followed by natural service. In Exp.3, cows were stratified within breed by age, postpartum interval, calf sex, and AI sire and were assigned within strata to one of two weaning treatments at the start of breeding, as described for Exp.1and 2. Estrous cycles of all cows were synchronized for AI using one of two protocols including 14 d CIDR + PGF2α 16 d following CIDR removal (primiparous cows) or a CIDR insert for 7 d with GnRH at CIDR insertion and PGF2α at CIDR removal (multiparous cows). Cows in Exp.2 and 3 were bred by AI approximately 12 h after observation of estrus or by timed AI at 80 h after PGF2α concurrent administration of GnRH. Artificial insemination (Exp.2), breeding season pregnancy rate, and day of conception was not influenced (P>0.10) by weaning treatment for Exp.1and 2. However, early weaned cows in Exp.3 had 12.0% greater (P=0.03) AI pregnancy rates and conception occurred 3.78 d earlier (P=0.03) than normal weaned cows. At the time of normal weaning, cows that had their calves removed at early weaning were heavier and had greater body condition (P<0.01)than normal weaned cows in each experiment. We conclude that early-weaning beef cows at the start of the breeding season improved BW gain and BCS allowing those females to enter winter in greater BCS then NW cows, but improvements in reproductive performance were inconsistent.