The use of hormonal treatments to improve reproductive performance of anestrous beef cattle in tropical climates.

Most of the world's bovine herd is found in tropical regions. Bos indicus predominates, due to their adaptation to the climate and management conditions. Anestrous is the main factor that negatively affects reproductive performance of animals bred in these regions of the globe. Several factors affect postpartum anestrous, including suckling and maternal-offspring bond, and pre- and postpartum nutritional status. The short duration of estrus and the tendency to show estrus during the night, greatly affect the efficiency of artificial insemination (AI) programs in B. indicus cattle managed in tropical areas. Several restricted suckling or weaning procedures (temporary or permanent), and hormonal treatments have been used to induce ovulation and cyclicity in postpartum cows. Most hormonal treatments are based on progesterone/progestogen (P4) releasing devices associated with estradiol benzoate (EB), or a combination of GnRH/PGF(2alpha)/GnRH (Ovsynch). Treatments with GnRH/PGF(2alpha)/GnRH has presented inconsistent results, probably due to the variable number of cows in anestrous. Treatments using P4 devices and EB have resulted in apparently more consistent results than Ovsynch programs in B. indicus cattle; however, pregnancy rates are low in herds presenting high anestrous rates and moderate to low body condition. The addition of an eCG treatment at the time of device removal, which increased plasma progesterone concentrations and pregnancy rates in anestrous postpartum suckled B. indicus cows, may be useful to improve reproductive performance of beef cattle in tropical climates.