The objectives were to evaluate pregnancy per AI (P/AI) of dairy cows subjected to the 5-day timed AI protocol under various synchronization and luteolytic treatments. Cows were either presynchronized or received supplemental progesterone during the synchronization protocol, and received a double luteolytic dose of PGF 2α, either as one or two injections. In Experiment 1, dairy cows (n = 737; Holstein = 250, Jersey = 80, and crossbred = 407) in two seasonal grazing dairy farms were randomly assigned to one of four treatments in a 2 × 2 factorial arrangement. The day of AI was considered study Day 0. Half of the cows were presynchronized (G6G: PGF 2α on Day -16 and GnRH on Day -14) and received the 5-day timed AI protocol using 1 mg of cloprostenol, either as a single injection (G6G-S: GnRH on Day -8, PGF 2α on Day -3, and GnRH + AI on Day 0) or divided into two injections of 0.5 mg each (G6G-T: GnRH on Day -8, PGF 2α on Day -3 and -2, and GnRH + AI on Day 0). The remaining cows were not presynchronized and received a controlled internal drug-release (CIDR) insert containing progesterone from GnRH to the first PGF 2α injection of the 5-day timed AI protocol, and 1 mg of cloprostenol either as a single injection on Day -3 (CIDR-S) or divided into two injections of 0.5 mg each on Days -3 and -2 (CIDR-T). Ovaries were examined by ultrasonography on Days -8 and -3 and plasma progesterone concentrations were determined on Days -3 and 0. In Experiment 2, 655 high-producing Holstein cows had their estrous cycle presynchronized with PGF 2α at 46 ± 3 and 60 ± 3 days postpartum and were randomly assigned to receive 50 mg of dinoprost during the 5-day timed AI protocol, either as a single injection or divided into two injections of 25 mg each. Pregnancies per AI were determined on Days 35 and 64 after AI in both experiments. In Experiment 1, presynchronization with G6G increased the proportion of cows with a CL on Day -8 (80.6 vs. 58.8%), ovulation to the first GnRH of the protocol (64.2 vs. 50.2%), and the presence (95.6 vs. 88.4%) and number (1.79 vs. 1.30) of CL at PGF 2α compared with CIDR cows. Luteolysis was greater for two injections compared to a single PGF 2α injection (two PGF 2α = 95.9 vs. single PGF 2α = 72.2%), especially in presynchronized cows (G6G-T = 96.2 vs. G6G-S = 61.7%). For cows not presynchronized, two PGF 2α injections had no effect on P/AI (CIDR-S = 30.2 vs. CIDR-T = 34.3%), whereas for presynchronized cows, it improved P/AI (G6G-S = 28.7 vs. G6G-T = 45.4%). In Experiment 2, the two-PGF 2α injection increased P/AI on Days 35 (two PGF 2α = 44.5 vs. single PGF 2α = 36.4%) and 64 (two PGF 2α = 40.3% vs. single PGF 2α = 32.6%) after AI. Presynchronization and dividing the dose of PGF 2α (either cloprostenol or dinoprost) into two injections increased P/AI in lactating dairy cows subjected to the 5-day timed AI protocol.
|Original language||English (US)|
|Number of pages||12|
|State||Published - Jul 15 2012|
- 5-Day timed AI protocol
- Dairy cow