hCG não é uma alternativa à eCG no protocolo de iatf em vacas bos indicus mas aumenta a eficiência dos protocolos de iatf em vacas que não apresentam estro

Abstract

The objective of this study was to evaluate the use of hCG at different times in the TAI protocol on the fertility of lactating Bos indicus cows. In experiments 1 and 2, the cows received an intravaginal progesterone (P4) device and 2 mg of estradiol benzoate (EB) on day zero (D0). In experiment 1, the device was removed after eight and a half days (D8.5; study A) or at seven days (D7; study B). At that moment of the P4 device removal, 500 µg of sodium cloprostenol (PGF2α) and 1 mg of an ovulation inducer (EB in study A and EC in study B) were administered. After the removal of the device, in study A, the cows in the control groups (n=320) did not receive additional treatment, while those in the eCG (n=316) and hCG (n=321) groups received 300 IU of eCG and 150 IU of hCG, respectively. Similarly, in study B, the cows in the control (n=146), eCG (n=151), and hCG (n=151) groups received the same aforementioned treatments. Artificial insemination occurred 36 hours after the removal of the P4 device in study A and 48 hours in study B. Ultrasonographic exams were performed on day zero (D0), on the day of the removal of the P4 device, and at insemination. Experiment 2 was subdivided into three studies (A, B, and C). In study A, cows in the control group (n=42) did not receive additional treatment, while the GnRH (n=44) and hCG (n=41) groups received 100 µg of gonadorelin and 1000 IU of hCG, respectively. Ultrasonographic examinations were performed on D0, D8, D10, D11, D12, and D22. In study B, the cows received the same treatments as in study A (Control; n=228, GnRH; n=227, and hCG; n=229). In study C, 500 IU of hCG were administered to the hCG500 group (n=162), 800 IU to the hCG800 group (n=165), and 1000 IU to the hCG1000 group (n=168). In studies A and B of experiment 1, a greater (P>0.05) follicular growth rate was observed in the eCG (P=0.003) and hCG (P=0.001) groups. The cows in the hCG group had greater rates of anticipated ovulation (P=0.001) and estrus expression (P=0.006). However, a lower pregnancy rate was observed in the cows of the hCG group (P=0.01) and the Control group (P=0.04). In experiment 2, cows treated with hCG showed greater ovulation rates (P=0.03; study A) and P/AI rates (P=0.04; studies B). In study C, the hCG1000 group achieved the greater pregnancy rates (P=0.05). It is concluded that hCG is not an alternative to eCG in the removal of the P4 device. However, the administration of 1000 IU of hCG at the time of insemination increases the fertility of Bos indicus cows that did not show estrus.