Effect of recombinant equine chorionic gonadotropin on fertility of lactating dairy cows.

Two experiments evaluated the effect of recombinant equine chorionic gonadotropin (reCG) on pregnancies per AI (P/AI) in lactating dairy cows. In Experiment 1, cows (n = 797) received a progesterone (P4)-insert and estradiol benzoate (EB) on Day0. Seven days later, P4-insert was removed and cows received prostaglandin F2α (PGF2α) and estradiol cypionate (ECP). Timed-AI was performed on Day9. On Day7, cows were randomly assigned to 1 of 3 groups: 1) Control, 2) 140 IU of reCG (reCG), or 3) 400 IU of serum-based eCG (seCG). The P/AI were greater for cows treated with eCG (27.8% vs. 37.2% vs. 36.8%, for Control, reCG, and seCG, respectively). In Experiment 2, cows (n = 591) received EB, double dose of GnRH, and a P4-insert on Day0. Seven days later, P4-insert was removed, and cows received PGF2α and ECP. On Day8, cows received a second PGF2α. On Day9, cows received GnRH and Timed-AI. On Day0, cows were randomly assigned to a 2x3 factorial arrangement of treatments to test the effects of 1) P4 load (0.75g vs. 2.0g of P4) in the P4-insert, and 2) dose of reCG on Day7 (Control vs. 105 IU of reCG vs. 140 IU of reCG). The P/AI was not affected by level of P4 (41.4% vs. 41.7%, for 0.75g and 2.0g of P4, respectively). Cows treated with reCG had more P/AI than Control cows (34.1% vs. 45.2% vs. 42.0%, for Control, 105reCG, and 140reCG, respectively). In conclusion, use of reCG increased P/AI in pasture and confined-based dairy cows, and is a viable alternative to seCG.