|Short, Robert - RETIRED ARS|
Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: May 1, 2004
Publication Date: June 15, 2004
Citation: Grings, E.E., Short, R.E., Heitschmidt, R.K. 2004. Post-weaning production of steers from varying calving and weaning strategies. Western Section of Animal Science Proceedings 55:126-129. Interpretive Summary: Calves from various calving seasons and weaning strategies may differ in weight at weaning in rangeland-based production systems. Profitability of post-weaning production of steer calves from these systems may then be influenced by the length of time in the feedlot and, potentially, carcass composition. We conducted a three year study to determine the post-weaning production characteristics of steers from various rangeland-based cow-calf production systems in the Northern Great Plains. Steers calves born in one of three calving seasons (late winter, early spring, or late spring) were weaned at one of two ages and fed until harvest. Body weight and carcass characteristics were collected at harvest. Calving season and weaning age affected the weight of steers entering the feedlot. The number of days in the feedlot was affected primarily by age of steers at weaning. Weight at harvest was impacted by calving season. We conclude that season of birth can impact growth and carcass composition independent of age of steers at weaning when harvested at equivalent fat thickness. This may be related to environmental factors both during the feeding period and before weaning. Calving season should, therefore, be considered in effective feedlot management strategies along with weaning age and weight at feedlot entry.
Technical Abstract: The impact of varied calving and weaning times on post-weaning production of steer calves from the Northern Great Plains was evaluated in a 3-yr study. Steers (n = 215) born in one of three calving seasons [late winter (LW), early spring (ES), or late spring (LS)] were weaned at 4 (LS1), 6 (LW1, ES1, LS2), or 8 (LW2, ES2) mo of age after grazing with their dams on native range. Later weaned cow-calf pairs continued to graze native range until weaning. Steers were pen-fed a corn silage and alfalfa hay-based diet until the weaning group averaged 375 kg. They were then moved to an individual feeding facility and fed a higher energy diet. Steers were individually allotted to harvest dates based upon visual estimates of fat thickness. Data were analyzed as a completely random design with fat thickness as a covariate using mixed model procedures. Year and year by treatment were random effects. Non-orthogonal estimates were used to delineate treatment effects. Initial steer weights averaged 216 ± 12 kg but were affected by calving season and age at weaning, with LS2 steers weighing 24 ± 10 kg less (P < 0.05) than the average of the LW1 and ES1, LW and ES steers weaned at 6 mo averaging 26 ± 8 kg less (P < 0.01) than those weaned at 8 mo of age, and LS1 weighing 26 ± 11 kg less (P < 0.05) than LS2. There were no treatment differences in ADG during the growing or finishing phases. Total days to harvest averaged 311 ± 15 d and differed between LW and ES steers weaned at 6 versus 8 mo of age due to a 37 ± 12 d difference (P < 0.01) in time to reach harvest. Total days to harvest did not differ between LS steers weaned at 4 versus 6 mo of age. Steers averaged 527 ± 12 kg at harvest and weights were 23 ± 10 kg less (P < 0.01) for ES than LW. Differences in production of steers among calving and weaning strategies may be related to differences in harvest weights and time on feed as affected by weaning weights.