EFFECTS OF CALF REMOVAL AT PARTURITION ON POSTPARTUM OVARIAN ACTIVITYIN ZEBU (BOS-INDICUS) COWS IN THE HUMID TROPICS

To assess endocrine and morphological responses of ovaries to total we aning at parturition, 6 Zebu (Bos indicus) cows 5 years or older were investigated. Following parturition, blood samples were collected dail y during the first month and twice weekly thereafter until day 60 to d etermine concentrations of progesterone (P-4) and prostaglandin F-2 al pha metabolite. It took between 25 to 32 days to complete uterine invo lution. The prostaglandin metabolite remained elevated for a mean peri od of 14.2 days (range, 4-21) postpartum. Five of the animals resumed cyclicity with a short estrous cycle starting between days 7 to 34 and lasting between 7 and 14 days. No estrous behavior was recorded prior to the short estrous cycles, but subsequent normal-length estrous cyc les were all preceded by signs of estrus. In the 1 animal that resumed cyclicity with an estrous cycle of normal length on day 37 (length 20 days), the cycle was preceded by estrous behavior. Progesterone conce ntrations reached a mean maximum of 4.8 nmol liter(-1) during the shor t estrous cycles, and prostaglandin metabolite concentrations peaked w hile P-4 concentrations were decreasing. P-4 concentrations reached a mean maximum of 12.2 nmol liter(-1) during the estrous cycles of norma l length. The interval from parturition to the first estrous cycle of normal length varied between 16 and 48 days, and the length of the cyc le was 18 to 22 days. Starting 2 days postpartum, ovaries from 5 of th e cows were scanned by ultrasonography every second day until day 30 p ostpartum. Medium-sized follicles were detected between days 4 to 7 po stpartum in 4 of the scanned cows that later had short estrous cycles. The time between parturition and the appearance of the first dominant follicle was 7.6 days (range 6-10 days). The interval between parturi tion and the appearance of the first ovulatory-sized follicle was 10.2 days (range 8-13 days). In 3 of the scanned cows this ovulatory-sized follicle ovulated. We conclude that cyclic ovarian activity in Zebu c ows can start early in the postpartum period in the absence of offspri ng, and that short luteal phases, not preceded by estrous behavior, ma y play an important role in establishing normal postpartum ovarian act ivity.