Post-Weaning Performance of Steers from Varying Calving and Weaning Strategies in Montana1

The impact of varied calving and weaning times on post-weaning production of steer calves was evaluated in a 3yr study. Steers (approximately 12 steers per calving-weaning treatment per year) born in late winter or early spring were weaned at 190 or 240 d of age, and steers born in late spring were weaned at 140 or 190 d of age after grazing with their dams on native range. Steers were pen-fed a growing diet until approximately 375 kg BW. They were then moved to an individual feeding facility and fed a higher-energy diet. Steers were allotted to harvest dates based upon visual estimates of degree of fat cover. Mixed model procedures were used to evaluate fixed effects of treatment and random effects of year and year × treat1This research was conducted under a cooperative agreement between USDA-ARS and the Montana Agric. Exp. Sta. USDA-ARS is an equal opportunity and affirmative action employer and all agency services are available without discrimination. Mention of a proprietary product does not constitute a guarantee or warranty of the product by USDA, Montana Agric. Exp. Sta., or the authors and does not imply its approval to the exclusion of other products that may also be suitable. 2To whom correspondence should be addressed: [email protected] 3Retired. ment. Predefined contrasts were used to delineate treatment effects. Initial steer BW was affected by calving system and age at weaning. No treatment differences in ADG during the growing phase or ADG, feed intake, or feed efficiency during the finishing phase occurred. Steers averaged 537 ± 4 kg at harvest and age at harvest did not differ among treatments. Late winter steers had greater hot carcass weights, marbling scores, and quality grades than early spring steers. Calving later in the calendar year without altering weaning times produced younger calves at weaning with lighter BW at the start of the feeding period, which required greater number of days from weaning to harvest and produced carcasses with less marbling and lesser quality grades.