Decreasing from 9 to 7 days the permanence of progesterone inserts make possible their use up to 5 folds in suckled Nellore cows

This study aimed to evaluate the effects of decreasing permanence period of progesterone (P4) inserts from 9 (9d) to 7 (7d) days in timed-AI (TAI) protocol, as well as their reuse on pregnancy per AI (P/AI) during 7d protocol. At the beginning of all protocols, cows received 2 mg of estradiol benzoate (EB) and a vaginal insert containing 1.9 g of P4. In the 7d protocol, the P4 insert was removed, and cows were given 25 mg of prostaglandin F2α, 0.6 mg of estradiol cypionate and 300 IU of eCG 7 days later. In the 9d protocol, the P4 insert was removed, and cows received the same hormones that were administrated in 7d protocol, however, they were applied on the 9th day of the protocol. In the experiment I, 302 suckled Nellore cows were undergone to 7d protocol, and AI was performed 10-14 h later after estrus detection. In the experiment II, 679 suckled Nellore cows were assigned to receive either 7d or 9d protocols. In the experiment III, 999 suckled Nellore cows were assigned to receive either a new P4 insert (CIDR1), or a P4 insert used previously for 7 (CIDR2), 14 (CIDR3), 21 (CIDR4) or 28 (CIDR5) days, and 227 Nellore heifers received a P4 insert used previously for 21 (CIDR4) or 35 (CIDR6) days during the 7d protocol. When 7d protocol was used, 45% of cows exhibited estrus 48 h after P4 removal. Thus, the AI was performed 55 h after P4 removal in experiments II and III when 7d protocol was used. There was no difference in estrus detection rate (72 vs 74%; P = 0.60), ovulation rate (80 vs 88%; P = 0.13) and P/AI (56 vs 54%; P = 0.49) between 7d and 9d protocols, respectively. In the 7d protocol, the P/AI was similar (P = 0.72) using a new P4 insert (47%), or a P4 insert used previously for 7 (48%), 14 (45%), 21 (54%), or 28 (49%) days in Nellore suckled cows. In addition, P/AI was similar (P = 0.15) in heifers that received a P4 insert used previously for 21 (52%), or 35 (61%) days during the 7d protocol. In conclusion, cows submitted to 7d or 9d protocols had similar reproductive performance, and the reuse of P4 inserts up to 6 folds (five in suckled cows plus one in heifers) did not affect reproductive performance of Nellore cattle in 7d protocol.