POSTPARTUM ANESTRUS IN CATTLE IN THE TROPIC

Both productivity and profitability in cattle operations are depending on the physiologic capacity of the cow to obtain one calf per year. The most important fact for achieving this goal is reducing the postpartum period, when pulses of luteinizing hormone (LH) are not enough to allow a final development and ovulation of dominant follicles. Two main factors affect this phenomenon: nutrition and suckling. Several metabolic signals act over the hypotalamus-hypophysis axis indicating the energy balance and allowing the onset of gonadotropin releasing hormone (GnRH) secretion and the onset of cycling. On the other hand, the calf generates endogenous endorphins secretion and inhibition of GnRH release. Further modulators of nutrition and suckling effects are age, parity, breed, heat stress and social factors (male and female effect). Generally, after the first ovulation, a short estrous cycle is shown, probably because of an early luteolisis in response to prostaglandin F2 alpha (PGF2α) release by the uterus; however, progesterone released by the short estrous cycle corpus luteum plays an important role on the establishment of the subsequent cyclicity