Factors affecting conception rate after artificial insemination and pregnancy loss in lactating dairy cows.

Objectives were to determine factors associated with conception rate (CR) and pregnancy loss (PL) in high producing lactating Holstein cows. In Study 1, CR was evaluated in 7633 artificial inseminations (AI) of 3161 dairy cows in two dairy farms. Pregnancy diagnosis was performed by palpation per rectum 39+/-3 days after AI. Environmental temperature was recorded at different intervals prior to and after AI. In Study 2, 1465 pregnancies from 1393 cows diagnosed at 31+/-3 days after AI by ultrasonography on three dairy farms were re-examined 14 days later to determine PL. Temperature > or =29 degrees C was considered to be heat stress (HS). Exposure to HS was defined as following: NH, no heat stress; HS1, exposure to at least 1 day of maximum temperature > or =29 degrees C and average daily maximum temperature (ADMT) <29 degrees C; and HS2, exposure to ADMT > or =29 degrees C. In Study 1, exposure of cows to HS1 and HS2 from 50 to 20 prior to AI was associated with reduced CR compared to cows not exposed to HS (28.8, 23.0, and 31.3%, respectively). Post-AI HS was not associated with CR. Cows inseminated following estrus detection or timed AI had similar CR. As the number of AI increased, CR decreased. Multiparous cows had lower CR than primiparous cows, and occurrence of milk fever and retained placenta was associated with decreased CR. In Study 2, PL was not associated with exposure to HS either prior to or after AI. Cows diagnosed with clinical mastitis experienced increased PL, but parity, number of AI, AI protocol, milk production, and days postpartum at AI were not associated with PL. In conclusion, CR was affected by HS prior to AI, parity, number of AI, and postparturient diseases, whereas PL was affected by clinical mastitis.