Effect of using 200 µg of gonadorelin at the first GnRH of the breeding-Ovsynch on ovulatory response and pregnancies per AI in first service lactating Holstein cows

This study aimed to determine if 200 μg of GnRH (gonadorelin hydrochloride) would increase ovulatory response and pregnancies per AI (P/AI) compared with 100 at the first breeding-Ovsynch a Double-Ovsynch program (DO) in lactating Holstein cows. Weekly cohorts primiparous (n = 719) multiparous 1,191) cows submitted DO [GnRH – 7 d PGF2α 3 (G1) (PG1) 1 ~32 h (G2) ~16 TAI] for timed-artificial insemination (TAI), randomly received either or G1 (primiparous, 64–75 DIM; multiparous, 59–70 DIM). Ovulation was determined by ultrasound 2 after 1,294) G2 1,020). Blood samples were collected PG1 evaluate serum progesterone (P4) concentrations. Conventional 314, Angus; n 1,084, Holstein) sexed-semen 276) used. Pregnancy diagnosed on 32, 46, 88, post-TAI. The high dose (200 μg) increased overall (81.3% vs. 65.1%), being similar between parities 72.2%; 73.9%). Mean P4 concentrations did not differ treatments (100 µg: 9.59 ± 0.15 ng/mL 9.43 ng/mL). Cows no ovulation had higher than (6.27 0.19 4.66 0.07 At PG1, proportion functional CL (98.7% 89.7%) (9.68 0.12 9.14 0.22 ng/mL) greater that ovulated ovulate. Also, from (5.26 3.32 0.25 improved P/AI 32 post-TAI inseminated conventional semen (54.6% 48.2%) tended improve 46 (48.8% 44.9%), 88 (47.6% 43.4%) (45.3% 41.2%) Primiparous better (58.2% 49.4%), (55.1% 44.4%), (53.2% 43.2%) (51.6% 40.7%) treated µg lower when sexed semen. In summary, Moreover, effect treatment depended type (conventional semen).