|Adams, Don - UNIV OF NEBRASKA|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 20, 1996
Publication Date: N/A
Interpretive Summary: When to wean calves and when and whether to supplement cows are major management decisions in a cow-calf enterprise. These decisions affect both economic and production efficiency, but little data are available under Northern Great Plains conditions to aid in making those decisions. Delaying weaning from September until December will usually result in an increase in weaning weight while utilizing native range forage, but that increase in weaning weight will come at the expense of decreased weights and condition scores of the cows in years when forage quantity and(or) quality is limiting. However, with mature cows and adequate nutritional inputs between weaning and breeding the next year, there may be no detrimental carryover effects on subsequent pregnancy rates and weaning weights, even if the delayed weaning has decreased precalving weights and condition scores of the cows. Protein supplementation during the fall will offset the negative effects of delayed weaning in years with limited forage resources and will consistently increase production efficiency and weaning weights primarily through increased milk production of the cow. The choice of genetic potential for calf growth and propensity to deposit fat will affect calf weaning weight and forage intake but not efficiency.
Technical Abstract: A 4-yr experiment was conducted to determine effects of protein supplementation, age at weaning, and calf sire breed on cow and calf performance during fall grazing. Crossbred cows nursing steer calves were assigned to a 2x2x2 factorial experiment. Treatment factors were: 1) no supplement (NS) or an individually fed supplement (S, 3 kg of a 34% protein supplement fed to cows every 3rd d); 2) calves weaned at the beginning (W, mid to late Sept.) or at the end (NW, mid to late Dec.) of the trial each yr; or 3) calves sired by Hereford or Charolais bulls. Change in cow weight and condition score were increased by S and W (P < .01), but these responses interacted and were not the same each yr (yr*S, yr*W, and yr*S*W, P < .01). Forage intake was decreased (P < .1) by W and S. Total intake (forage + supplement) was not affected by S but was decreased by W (P < .1). Digestibility of OM was decreased by S (P < .01). There were no carryover effects by the next fall in weaning weights or pregnancy rates. Milk yield decreased during the experimental period, and S maintained higher milk production in late lactation (P < .01). Calf ADG was increased by S and Charolais sires (P < .01). Efficiency (mg output/kcal input) was not affected by sire breed but was enhanced by S (P < .01). Our conclusions are: 1) effects of S on cows were to increase calf gains and improve persistency of lactation and efficiency; 2) delaying W decreased cow weight and condition score; 3) effects of W and S were highly dependent on forage and environmental conditions in any given year; and 4) effects did not carry over to next year's production.