|Paterson, J - MONTANA STATE UIVERSITY|
|Lipsey, R - AMERICAN SIMMENTAL ASSOC|
Submitted to: Livestock Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 1, 2012
Publication Date: June 13, 2012
Citation: Waterman, R.C., Geary, T.W., Paterson, J.A., Lipsey, R.J. 2012. Early weaning in Northern Great Plains beef cattle production systems: I. Performance and reproductive response in range beef cows. Livestock Science 148:26-35. Interpretive Summary: Beef cattle operations may optimize cow performance by early weaning calves during times when forage quantity and/or quality are insufficient to meet cow requirements (e.g., drought) or when there is concern about impacts of low body condition on cow reproductive success (i.e. young cows). Lactation places additional nutritional demands on beef cows, especially during periods of drought. Increases in milk yield have shown to increase forage dry matter intake during lactation Suckling has also been shown to delay the onset of estrus in beef cows and early weaning before the breeding season has been found to shorten the postpartum anestrous period and increased conception rates. Primiparous heifers have benefited from higher planes of nutrition when compared to multiparous cows during the anestrous, which would again suggest a benefit to early weaning. Weaning calves can increase the opportunity for cows to gain weight and improve body condition before winter. This may facilitate over-wintering cows using less harvested feedstuffs than would be necessary for them to achieve a specific targeted BCS at calving with normal autumn weaning. Under some circumstances, EW may also increase the likelihood of the cow becoming pregnant early in the breeding season.
Technical Abstract: Early weaning of spring born calves may be an alternative management strategy during drought and may help facilitate rebreeding of young cows. Our objective was to determine effects of early weaning at the start of breeding on cow reproductive performance with or without estrous synchronization and AI in the Northern Great Plains. In experiment 1 and 2, crossbred cows (predominantly Angus (= 75%) with Hereford, Red Angus, Charolais, and Tarentaise making up the remainder) at the USDA-ARS, Fort Keogh Livestock and Range Research Laboratory were stratified within cow age, postpartum interval, and calf sex and were assigned within strata to one of two weaning treatments at the start of breeding when calves were approximately 80-d of age. Cow in experiment 1 were natural mated at time of early weaning whereas cows in experiment 2 were exposed to estrous synchronized for AI using a CIDR for 7 d with GnRH at CIDR insertion and PGF2a at CIDR removal. In experiment 3, at the Judith Gap, MT location, Angus and Angus × Simmental 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. Estrous cycles of all cows were synchronized for AI using one of two protocols including 14 d CIDR + PGF2a 16 d following CIDR removal (primiparous cows) or a CIDR insert for 7 d with GnRH at CIDR insertion and PGF2a at CIDR removal (multiparous cows). Cows in experiment 2 and 3 were observed for estrus continuously during daylight hours from PGF2a injection until 72 h after PGF2a at which cows were time AI with second administration of GnRH. Artificial insemination, seasonal pregnancy rate and d of conception was not influenced (P > 0.05) by weaning treatment for experiment 1 and 2. However, cows that had their calves removed at time of PGF injection resulted in a 12.4 % increase (P < 0.05) in AI pregnancy rates and a 4 d earlier (P < 0.05) day of conception in experiment 3. After 133-d (time from early to normal weaning) cow body weights increased (P <0.001) for all early weaned cows and for normal weaned cows in experiment 3. We conclude that early weaning beef cows at the beginning of the breeding season improves weight gain and allows less harvested feeds to be fed during winter to calve at similar body conditions of normal weaned cows.