Performing AI 55 or 65 h after progesterone device removal did not differ in a 7-d progesterone-based protocol for timed-AI in Nellore suckled cows

This study aimed to evaluate the reproductive performance of Nellore suckled cows inseminated 55 ( n = 304) or 65 ( n = 296) h after progesterone (P4) removal in a 7-d protocol. The protocol consisted of the insertion of a device with 2 g of P4 and 2 mg of estradiol benzoate on d 0, with the device remaining in the cows for 7 d. Cows in the 55-h treatment had the P4 device removed in the morning, while cows in the 65-h treatment had the P4 device removed in the afternoon. At P4 removal, cows received intramuscularly 300 IU of eCG, 0.6 mg of estradiol cypionate and 0.52 mg cloprostenol sodium. Artificial insemination was performed according to treatments (55 vs. 65 h after P4 removal). The results of the study showed that the estrus detection rate (69% vs 65%) and pregnancy per AI (P/AI; 49% vs 49%) did no differ in cows inseminated 55 or 65 h after P4 removal, respectively. Furthermore, ovulation rate, the diameter of the largest follicle at the time of AI, and P4 concentration after AI were not affected by treatments. The probability of P/AI was not affected by parity, BCS, age, diameter of largest follicle at AI, days postpartum, BW and time to AI. This study suggests that performing AI from 55 to 65 h after the P4 removal in the 7-d-P4 protocol did not affect the reproductive performance in Nellore cows, and opens the possibility for producers to take more time to perform AI of cows in the field without affecting P/AI.