Reproductive responses and calf birth and weaning weights as affected by body condition at parturition and postpartum weight gain in primiparous beef cows.

Effects of body condition score (BCS) at parturition and postpartum weight gain on reproduction and production responses were evaluated using 240 primiparous (21 to 28 mo) beef cows calving in 60-d periods in three states over 3 yr. Cows were randomly allotted 90 d before parturition and fed to achieve BCS of 4, 5, or 6 (1 = emaciated, 9 = obese) at parturition. After parturition, one-half of these cows (within state) were group-fed to gain .45 kg/d (moderate) or .90 kg/d (high) until the start of a 60-d breeding season. Cows calving in BCS of 4, 5, or 6, respectively, had calves with progressively heavier (P < .05) birth weights, but dystocia score was not influenced by BCS at calving. Parturient BCS of cows had no effect on actual or 205-d adjusted weaning weights of calves. Birth weights, dystocia score, and actual and 205-d adjusted weaning weights were affected by location (P < .05). Cows with greater weight gains postpartum had calves with heavier (P < .05) actual and 205-d adjusted weaning weights than did cows with moderate weight gains. No significant interactions among location, BCS, or postpartum nutrition-group were observed for any of the production variables described above. Greater BCS at calving resulted in more (P < .05) cows in estrus and more (P < .05) cows pregnant by 40 and 60 d of a breeding season. Luteal activity by start of breeding, as well as estrus responses and pregnancy rates at 20, 40, or 60 d of a breeding season, were affected by location (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)