FAT SUPPLEMENTATION INFLUENCES POSTPARTUM REPRODUCTIVE-PERFORMANCE INBRAHMAN COWS

Multiparous Brahman cows (n = 40) in excellent body condition (6.5 +/- .1) were randomly assigned to receive either 5.2 (rice bran) or 3.7% (control) dietary fat after calving. The experimental diets were formu lated to be isocaloric and isonitrogenous. The experimental diets were fed twice daily from d 1 after calving through the first normal estro us cycle. Cows were weighed, scored for body condition, and bled at we ekly intervals from d 1 through 50 after calving. Weekly bleedings con tinued until, the first detectable estrus. Blood samples were collecte d daily throughout the first normal estrous cycle. All cows were expos ed to a fertile bull at the estrus following the first normal estrous cycle and for a 60-d breeding season. Ovarian follicular populations w ere recorded weekly by transrectal ultrasonography from d 15 to 50 aft er calving. Calf weights were recorded at 14-d intervals from d 1 to 4 3 after birth and at weaning (205 d). Cows receiving rice bran gained more body condition (P <.05) than cows receiving the control supplemen t. The numbers of small (< 4.0 mm, P <.05), medium (4.0 to 7.9 mm, P < .05) and total follicles (P <.05) were greater in the rice bran than i n the control group from 15 to 29 d after calving, and large follicles (greater than or equal to 8.0 mm) increased in number (P <.05) and th e largest follicle increased in size (P <.001) over time regardless of the level of dietary fat. Fat supplementation increased the numbers o f medium (P <.01), large (P <.05), and total (P <.01) follicles and si ze of the largest follicle (P < .05) during the 3 wk before the first normal estrous cycle. ?Pie intervals from parturition to reproductivel y important end points were similar (P >.10) between dietary treatment s as well as the percentage of cows showing normal or abnormal estrous cyclic activity. Treatment did not affect (P >.10) daily serum proges terone (P-4) concentrations. However, there was a tendency (P = .09) f or more rice bran-supplemented cows to be pregnant (94.1 vs 71.4%) aft er being exposed to a fertile bull for 60 d. Calf weight gain tended t o be higher (P = .08) in calves nursing rice bran-supplemented dams. I n conclusion, using rice bran, with high concentrations of oleic and l inoleic acids, as a fat supplement for postpartum cows enhanced ovaria n follicular growth before normal estrous cycles resumed and increased body condition scores and pregnancy rates without altering postpartum interval or serum P-4 concentrations.