Fertility of crossbred dairy cows submitted to FTAI with eCG

The aim of this study was to evaluate the effect of eCG on fertility of crossbred (Bos taurus x Bos indicus) lactating cows submitted to a protocol of fixed time AI (FTAI) between October and November 2013. A total of 265 cows was used, 165 multiparous and 100 primiparous, with an average milk production of 24.3 ± 0.47 kg/d and average of 127.7 ± 5.38 DIM. At a random day of the estrous cycle all cows received an intravaginal progesterone device (CIDR®, Zoetis, Brazil), 2 mg estradiol benzoate im (Gonadiol®, MSD, Brazil) and 100 μg gonadorelin (Fertagyl®, MSD, Brazil) in the morning (D0). At D7 morning, all cows received 0.5 mg D-Cloprostenol im (Sincrocio®, Ouro Fino, Brazil) and were randomly assigned into two groups: eCG (n = 132) – received 400 IU eCG im (Novormon®, MSD, Brazil); and Control (n = 133) – did not receive eCG. At the afternoon of D8, devices were removed and all cows received 0.5 mg D-Cloprostenol im and 1 mg estradiol benzoate im. The FTAI was performed at D10 morning. Diagnosis and confirmation of pregnancy were performed 30 and 60 days after AI. Data were analyzed by PROC GLIMMIX of SAS and the results are presented as least squares means ± SE following eCG and Control groups, respectively. Pregnancy per AI (P/AI) at 30 (37.1 ± 5.4% vs. 22.3 ± 4.5%; P = 0.02) and 60 (27.8 ± 5.1% vs. 16.1 ± 4.0%; P = 0.03) days was higher in eCG group. However, pregnancy loss did not differ between groups (19.6 ± 7.6% vs. 21.5 ± 10.4%; P = 0.80). Furthermore, there was a tendency (P = 0.11) for interaction between the use of eCG and the number of previous postpartum services. Cows treated with eCG and inseminated at 1st AI postpartum had higher P/AI at 30 (42.6 ± 8.2% vs. 18.1 ± 6.0%; P = 0.02) and 60 (32.3 ± 7.9% vs. 12.0 ± 4.9%; P = 0.08) days. When cows were divided according to milk production: higher (30.0 kg/d; n = 134) or lower (18.5 kg/d; n = 131), there was also a tendency for interaction (P = 0.11). Higher producers that received eCG had higher P/AI at 30 (36.0 ± 7.3% vs. 15.0 ± 4.4%; P < 0.01) and 60 (26.5 ± 6.7% vs. 10.2 ± 3.5%; P < 0.01) days. However, in lower producers this did not happen at 30 (30.8 ± 15.8% vs. 25.2 ± 16.6%, P = 0.48) nor at 60 (29.2 ± 6.1% vs. 24.7 ± 6 5%, P = 0.48) days. It is concluded that the use of eCG on D7 of the protocol increases fertility of crossbred dairy cows submitted to FTAI.