title: Pregnancy per AI differences between primiparous and multiparous high-yield dairy cows after using Double Ovsynch or G6G synchronization protocols.
abstract: The objective of the present work was to determine the optimal protocol for timed AI on high-yield dairy cows. The pregnancy per AI (pregnancy/AI) arising from 7805 first timed artificial inseminations on 27 dairy farms in eastern Spain was examined after use of the Double Ovsynch (DOv; N = 6783) or G6G (N = 1022) synchronization protocols. Parity number, farm, prostaglandin analogue, and season (hot or cool) were examined for their possible association with postsynchronization fertility (in terms of pregnancy/AI). Mean pregnancy/AI overall was 36.1 ± 8.4%, with no significant differences between the DOv or G6G protocols (36.3 ± 8.3% vs. 34.8 ± 9.1%). However, parity and synchronization treatment resulted in a significant interaction (P = 0.03). When DOv AIs (N = 6783) and G6G AIs (N = 1022) were analyzed separately it was observed that pregnancy/AI was significantly better in primiparous than in multiparous cows after DOv (44.3 ± 11.4% vs. 31.4 ± 8.2%; P < 0.0001), and pregnancy/AI was similar after G6G in primiparous and in multiparous cows (34.7 ± 9.2% vs. 34.8 ± 9.9%). Hot season significantly reduced pregnancy/AI to a similar extent for primiparous and multiparous cows and showed a significant interaction of protocol and season (P = 0.001). These results were similar across all farms, regardless that their overall pregnancy/AI was similar or significantly different from the average. These results indicate that G6G tended to be associated with a higher pregnancy/AI than DOv in multiparous cows, and the opposite was observed in primiparous cows.
authors: Departamento Reproducción Animal, INIA, Madrid, Spain. susana.astiz@terra.es
authors: S
authors: S
authors: Astiz
authors: O
authors: O
authors: Fargas
mesh_terms: D000818:Animals; D002064:Buserelin / Q000494:pharmacology; D002417:Cattle / Q000502:physiology*; D002980:Climate; D003612:Dairying / Q000379:methods; D004973:Estrus Synchronization / Q000379:methods*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D007315:Insemination, Artificial / Q000379:methods; D016015:Logistic Models; D010298:Parity; D011247:Pregnancy; D018873:Pregnancy Rate; D012621:Seasons; D013696:Temperature
chemical_list: D007987:Gonadotropin-Releasing Hormone; D002064:Buserelin