EFFECTS OF TIME OF WEANING, SUPPLEMENT, AND SIRE BREED OF CALF DURINGTHE FALL GRAZING PERIOD ON COW AND CALF PERFORMANCE

A 4-yr experiment was conducted to determine effects of protein supple mentation, age at weaning, and calf sire breed on cow and calf perform ance during fall grazing. Each year 48 pregnant, crossbred cows nursin g steer calves ((x) over bar calving date April 8) were assigned to a 2 x 2 x 2 factorial experiment replicated in three native range pastur es. Treatment factors were: 1) no supplement(NS) or an individually fe d supplement (S, 3 kg of a 34% protein supplement fed to cows every 3r d d); 2) calves weaned at the beginning (W, mid to late September) or at the end (NW, mid to late December) of the trial each year; or 3) ca lves sired by Hereford or Charolais bulls. Data were adjusted for cow size (initial hip height and initial and final weights and condition s cores) by analyses of covariance using principal component coefficient s as covariates. Change in cow weight and condition score were increas ed by S and W (P <.01), but these responses interacted and were not th e same each year (yr x S, year x W, and year x S x W, P <.01). Forage intake was decreased (P <.1) by S and W. Total intake (forage + supple ment) was not affected by S but was decreased by W (P <.1). Digestibil ity of OM was decreased by S (P <.01). Some carryover effects of treat ments were observed the next spring in cow weight, condition score, an d birth weight (NW decreased birth weight by 2 kg, P <.01), but there were no effects by the next fall on weaning weights or pregnancy rates . Milk yield decreased during the experimental period, and S maintaine d higher milk production in late lactation (P <.01). Calf ADG was incr eased by S and Charolais sires (P <.01). Efficiency (grams of output/m egacalorie of input) was not affected by sire breed but was enhanced b y S (P <.01). Our conclusions are that 1) effects of feeding a 34% pro tein supplement to cows were to increase calf gains and improve persis tency of lactation and efficiency; 2) delaying weaning decreased cow w eight and condition score; 3) effects of weaning age and protein suppl ementation were highly dependent on forage and environmental condition s in any given year; and 4) whatever effects existed in a given year d id not carry over to effects on next year's production as measured by pregnancy rates and weaning weights.