EFFECTS OF POSTPARTUM NUTRITION AND ONCE-DAILY SUCKLING ON REPRODUCTIVE EFFICIENCY AND PREWEANING CALF PERFORMANCE IN FALL-CALVING BRAHMAN (BOS-INDICUS) COWS

Brahman cows were used to evaluate the effects of postpartum nutrition and suckling on reproductive and calf performance. Cows received high or low TDN and once-daily or unrestricted suckling. High TDN (H; 111% of NRC recommendation) cows received a 75% corn:25% soybeam meal diet . Low TDN (L; 93% of NRC recommendation) cows received no concentrates . Once-daily suckled (restricted, R) cows nursed calves for 30 min/d s tarting at d 21 after calving. In the unrestricted (U) suckling groups , calves had continuous access to cows. By 2 wk of suckling restrictio n, more (P < .01) R than U cows had progesterone concentrations of gre ater-than-or-equal-to .7 ng/mL (55 vs 0%) and more (P < .05) HR than L R cows had progesterone concentrations greater-than-or-equal-to .7 ng/ mL (70 vs 40%). All groups had increases in progesterone and 13,14-dih ydro-15-keto-prostaglandin F2alpha before estrus. The interval to firs t estrus was shorter (P < .01) for R than for U cows (42 vs 65 d). By d 42 postpartum, more (P < .01) R than U cows exhibited estrus (67 vs 0%), and more (P < .05) HR than LR cows exhibited estrus (89 vs 44%). Calving interval was shorter (P < .01) for R than for U cows (361 vs 3 95 d). Initial ADG were lower (P < .01) for R than for U calves (.02 v s .69 kg), but weaning weights were similar. Once-daily suckling permi tted ovarian activity, hastened return to estrus, and reduced calving interval without reducing weaning weights. Increased postpartum energy intake enhanced the response to restricted suckling.