PREPARTUM BODY CONDITION AND WEIGHT INFLUENCES ON REPRODUCTIVE-PERFORMANCE OF FIRST-CALF BEEF-COWS

Data were collected on 476 spring-calving, primiparous cows at six loc ations in Louisiana over a 2-yr period. Objectives of the study were t o evaluate changes in prepartum body condition score (BCS) and BW of h eifers when fed varying energy levels and to determine the influences of prepartum BCS and BW changes and BCS at calving on postpartum trait s. Heifers were allocated to one of three energy levels from approxima tely 90 d prepartum to parturition. The diets were formulated to provi de low, recommended, and high energy levels based on TDN requirements. After calving, cows were placed on annual ryegrass pasture and manage d similarly at each location. Weight and BCS at calving were greater(P < .05) for females with higher BCS at 90 d prepartum (IBCS) and for t hose assigned to higher energy levels. Calving and calf growth traits were not affected (P > .05) by IBCS, energy level, prepartum changes i n BCS and BW, or BCS at calving. Prepartum changes in BCS and BW regul ated by varying energy levels had no effect (P > .05) on postpartum re production; however, BCS at calving influenced (P < .03) pregnancy rat e and days to pregnancy. Cows with BCS 6 and 7 at calving had higher ( P < .05) pregnancy rates (87.0 and 90.7%) than those with BCS 4 and 5 (64.9 and 71.4%). Interval to pregnancy for cows with BCS 4 at calving was 10 to 18 d longer (P < .05) than for those with BCS greater than or equal to 5. These results indicate that body condition of primiparo us cows at calving is a reliable indicator of subsequent; reproductive performance regardless of prepartum BCS and BW changes.