Fertility programs for lactating dairy cows: a novel Presynch + Timed AI program (Double E-Synch) produces similar ovarian dynamics, synchronization, and fertility as Double-Ovsynch.

Fertility programs were implemented for the first postpartum timed-AI (TAI) in 800 (primiparous and multiparous) lactating dairy cows, evaluating 2 presynchronization (presynch) strategies and 2 TAI protocols, in a 2 × 2 factorial arrangement. Weekly, cows were enrolled into 1 of 4 groups (Ovs+Ovs [Double-Ovsynch], Ovs+OvsP4/E2, PreP4/E2+Ovs and PreP4/E2+OvsP4/E2 [Double E-Synch). On d -17 (34 ± 3 d in milk), the Ovs presynch was initiated with 10 µg of buserelin acetate (GnRH), and cows received 0.5 mg of cloprostenol sodium (PGF) on d -10, and 10 µg of GnRH on d -7. The PreP4/E2 presynch was initiated on d -17 with a used 2 g P4 insert, which was removed on d -10, together with 0.5 mg of PGF and 1 mg of E2 cypionate (EC). For TAI protocols, Ovs group received on d 0: 20 µg of GnRH (double dose), d 7: PGF, d 8: PGF, d 9.5: 10 µg of GnRH, and d 10: TAI (16 h after GnRH). Cows submitted to OvsP4/E2 received on d 0: 20 µg of GnRH (double dose) and a new 2 g P4 insert, d 7: PGF, d 8: P4 insert removal, PGF and EC, and d 10: TAI (48 h after P4 insert removal). The GLIMMIX procedure of SAS 9.4 was used for statistical analyses (P ≤ 0.05). The presence of CL on d -17 (average = 68.8% [550/800]) was similar among treatments. The presence of CL on d 0 of TAI protocols was high, and Ovs as a presynch increased percentage of cows with CL (95.5 [382/400] vs. 90.8% [363/400]). However, at the first PGF of the breeding (TAI) protocols (d 7), there was no effect of presynchronization program and 98.5% (788/800) of the cows had at least 1 CL. Ovulation after d 0 was greater in cows submitted to PreP4/E2 than Ovs (72.0 [288/400] vs. 64.3% [257/400]), and those ovulating had greater P/AI (51.0 [278/545] vs. 41.6% [106/255]). Overall, multiple ovulations after TAI were low and similar between TAI protocols and presynch strategies (7.2% [54/753]). Expression of estrus in OvsP4/E2 protocols was greater than Ovs (69.4 [274/395] vs. 41.5% [168/405]), and an interaction was detected, in which cows not expressing estrus ovulated more after TAI in Ovs compared with OvsP4/E2 protocol (93.3 [221/237] vs. 77.7% [94/121]). Cows expressing estrus had greater P/AI in both Ovs (58.3 [98/168] vs. 42.2% [100/237]) and OvsP4/E2 (57.3 [157/274] vs. 24.0% [29/121]). There was no interaction between presynch and TAI protocol on P/AI on d 32 of cows that ovulated after TAI (48.4, 49.7, 53.3, and 52.5% for Ovs+Ovs [Double-Ovsynch], Ovs+OvsP4/E2, PreP4/E2+Ovs and PreP4/E2+OvsP4/E2 [Double E-Synch], respectively), and no differences in pregnancy loss between d 32 and 90 (average = 24.0% [92/384]). In conclusion, the study validated 2 presynchronization strategies and 2 TAI protocols, establishing 4 possible fertility programs, all of them producing well-controlled ovarian dynamics, excellent synchronization, and high fertility. Moreover, Double-Ovsynch and Double E-Synch both produced similar results, despite differences in pharmacological bases.