EXERCISE AND INDUCED-PARTURITION EFFECTS ON DYSTOCIA AND REBREEDING IN BEEF-CATTLE

The study involved 44 primiparous, 2-yr-old heifers and 74 multiparous cows, 3 or 4 yr old, bred to a single Charolais bull. Variables were dam age (heifer, H; or cow, C), restricted (RE) or forced (FE) exercis e for the last 90 d precalving, and natural (NP) or induced (IF) partu rition. The RE dams were held in drylots; FE dams were on range until d 260 to 267 and walked 3.2 km/d for feed and water. Dams with IP rece ived 10 mg of flumethazone on d 269 of gestation. Diets for FE and RE dams contained the same hay and grain, but FE dams were fed in amounts projected to give weight changes approximating those of RE dams. All dams were calved in drylots; thereafter, all pairs were maintained tog ether on pasture to the end of the study. Exercise did not affect dyst ocia score or incidence, increased feed requirement 31% (P < .01), and gave a 14.8% higher (P < .05) pregnancy rate in the subsequent 45-d b reeding season. We hypothesize the increased pregnancy may have result ed from a feed-endocrine effect related to body weight gain, body comp osition-metabolic changes, or subsequent higher feed intake. Induced c alving shortened gestation length 8 d (P < .01), reduced calf birth wt 2.4 kg (P < .01), increased the incidence of retained fetal membranes (RFM) 60.3% (P < .01), increased interval from calving to first estru s 7.6 d (P < .05), and reduced calf weaning weight 6.9 kg (P < .15). B ody weights and calf birth weights from C exceeded those of H (P < .05 to < .01), and more C (47.1%; P < .01) showed estrus by beginning of the breeding season and had 20.4-d shorter (P < .01) postpartum interv al than H. We conclude that gestation exercise increased feed requirem ents, had no significant effect on parturition traits, and increased s ubsequent pregnancy rate; induced calving increased the incidence of R FM, increased the postpartum interval, and decreased subsequent pregna ncy rate.