The ability of different hormones administered on day five of the estrous cycle to increase pregnancy rates was studied in 196 recipient crossbred Holstein-Zebu heifers, randomly assigned to four treatments: T1-control (n=50), T2- subcutaneous administration of 500mg of rbST (n=44), T3- intramuscular administration of 100m g of GnRH (gonadorelin; n=46) and T4-administration of 3000IU of hCG (1000IU endovenous and 2000IU intramuscular; n=56). Seven-day embryos were equally distributed (stage and quality) and transferred to recipient heifers on day seven of the estrous cycle. Pregnancy rates detected on day 53 after embryo transfer did no differ among treatments, being: 15/24 in T1 (62.5%), 15/25 in T2 (60.0%), 13/29 in T3 (44.8%) e 22/31 in T4 (71.0%). The results showed that administration of rbST, or GnRH or hCG on day five of the estrous cycle was not capable to increase pregnancy rates.
Cattle; Nelore; embryo; rbST; GnRH; hCG
