ARS | Publication request: PERFORMANCE OF EARLY WEANED (~80 D) VS NORMAL WEANED (~215 D) COWS IN THE NORTHERN GREAT PLAINS

Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: May 15, 2006
Publication Date: June 15, 2006
Citation: Geary, T.W., Waterman, R.C., Paterson, J.A., Ansotegui, R.P., Lipsey, R.J. 2006. Performance of early weaned (~80 d) vs normal weaned (~215 d) cows in the northern great plains. Western Section of Animal Science Proceedings 57:99-102.

Interpretive Summary: Our objective was to determine effects of early weaning at the start of breeding on cow reproductive performance following AI with a 50-d cleanup breeding season among cows in the Northern Great Plains. Angus (n = 199) and Angus x Simmental (n = 158) cows stratified within breed by age, postpartum interval, calf sex, and AI sire were assigned within strata to one of two weaning treatments. Cows (n = 232) receiving early weaning (EW ' 80 d) had calves permanently removed at the time of prostaglandin (PGF) injection and start of AI breeding. Cows (n = 125) receiving normal weaning (NW) were suckled by calves until weaning at approximately 215 d of age. Estrous cycles of all cows were synchronized for AI using a protocol including 14 d progesterone insert (CIDR) + PGF 16 d following CIDR removal (primiparous cows) or a CIDR insert for 7 d with gonadotropin releasing hormone (GnRH) at CIDR insertion and PGF at CIDR removal (multiparous cows). Cows detected in estrus within 72 h after PGF were inseminated approximately 12 h later. Cows not detected in estrus by 72 h after PGF received timed AI with GnRH at 80 h after PGF (d 0). Bulls were placed with cows beginning 2 wk after AI for the remainder of a 50-d breeding season. Pregnancy rates from AI were higher (P < 0.05) for early weaned cows (66%) compared to normal weaned cows (54%). Cow age and age by weaning treatment had no effect (P > 0.10) on AI pregnancy rates. Breeding season pregnancy rates tended (P = 0.12) to favor cows that were early weaned (94%) compared to normal weaned (89%). Date of conception was 7 d earlier (P < 0.05) for early weaned cows compared to normal weaned cows. Early weaned cows gained more weight during the grazing period and were 36 kg heavier than normal weaned cows at the time of normal weaning (P < 0.01). Primiparous early weaned cows were 65 kg heavier than primiparous normal weaned cows. We conclude early weaning at the start of a synchronized breeding season increased AI pregnancy rates and cow weights at the time of normal weaning. Early weaning may be a viable alternative to culling cows during periods of low forage production in the Northern Great Plains.

Technical Abstract: Our objective was to determine effects of early weaning at the start of breeding on cow reproductive performance following AI with a 50-d cleanup breeding season among cows in the Northern Great Plains. Angus (n = 199) and Angus x Simmental (n = 158) cows stratified within breed by age, postpartum interval, calf sex, and AI sire were assigned within strata to one of two weaning treatments. Cows (n = 232) receiving early weaning (EW ' 80 d) had calves permanently removed at the time of prostaglandin (PGF) injection and start of AI breeding. Cows (n = 125) receiving normal weaning (NW) were suckled by calves until weaning at approximately 215 d of age. Estrous cycles of all cows were synchronized for AI using a protocol including 14 d progesterone insert (CIDR) + PGF 16 d following CIDR removal (primiparous cows) or a CIDR insert for 7 d with gonadotropin releasing hormone (GnRH) at CIDR insertion and PGF at CIDR removal (multiparous cows). Cows detected in estrus within 72 h after PGF were inseminated approximately 12 h later. Cows not detected in estrus by 72 h after PGF received timed AI with GnRH at 80 h after PGF (d 0). Bulls were placed with cows beginning 2 wk after AI for the remainder of a 50-d breeding season. Pregnancy rates from AI were higher (P < 0.05) for early weaned cows (66%) compared to normal weaned cows (54%). Cow age and age by weaning treatment had no effect (P > 0.10) on AI pregnancy rates. Breeding season pregnancy rates tended (P = 0.12) to favor cows that were early weaned (94%) compared to normal weaned (89%). Date of conception was 7 d earlier (P < 0.05) for early weaned cows compared to normal weaned cows. Early weaned cows gained more weight during the grazing period and were 36 kg heavier than normal weaned cows at the time of normal weaning (P < 0.01). Primiparous early weaned cows were 65 kg heavier than primiparous normal weaned cows. We conclude early weaning at the start of a synchronized breeding season increased AI pregnancy rates and cow weights at the time of normal weaning. Early weaning may be a viable alternative to culling cows during periods of low forage production in the Northern Great Plains.