hCG is not an alternative to eCG in the TAI protocol in Bos indicus cows, but it increases the efficiency of TAI protocols in cows that do not show estrus.

The study evaluated the use of hCG at different times in the TAI protocol on the fertility of Bos indicus cows. In Experiment 1, cows received a progesterone device and 2 mg of estradiol benzoate (EB) on D0. The device was removed on D8.5 (study A) or D7 (study B), followed by 500 µg of cloprostenol and 1 mg of EB or estradiol cypionate. At this moment, cows were assigned to Control (no treatment), eCG (300 IU), or hCG (150 IU) groups. TAI occurred 36 h (A) or 48 h (B) post-device removal. In Experiment 2, in studies A and B, treatments [Control, GnRH (100 µg), or hCG (1000 IU)] were administered at TAI. In study C, cows received or did not receive 500, 800, or 1000 IU of hCG at TAI. In Experiment 1, cows of the control group had lower follicular growth (P < 0.01), and cows of the hCG group had greater estrus expression (P = 0.006) and early ovulation (P = 0.001). However, the cows of the hCG and control groups had lower P/AI (P = 0.01). In Experiment 2, cows of the hCG group had greater ovulation rates (P = 0.03) and pregnancy rates (P = 0.04). In study C, 1000 IU of hCG at TAI increased (tendency) the fertility (P = 0.07). In conclusion, hCG is not an effective alternative to eCG at device removal. However, 1000 IU of hCG at the time of insemination improves fertility in cows that did not express estrus. • hCG at the time of progesterone device removal decreases the P/AI rate. • hCG at AI increases ovulation and CL vascularization in cows without estrus. • hCG at AI increases the P/AI rate in cows that did not show estrus.