Effect of presence of clinical and subclinical endometritis at the initiation of Presynch–Ovsynch program on the first service pregnancy in dairy cows

The present study examined the effect of presence of clinical or subclinical endometritis at the initiation of Presynch–Ovsynch estrous synchronization program on the first service pregnancy rate in dairy cows. Lactating Holstein cows (N = 275) were given a thorough reproductive examination at 32–38 days in milk, 3 days prior to the scheduled start of Presynch–Ovsynch program. Based on the reproductive exam findings the cows were diagnosed and classified into three groups as clinical endometritis, subclinical endometritis and normal. All cows received two set-up injections of 25 mg PGF2α (Lutalyse®, Pfizer Animal Health, New York, NY, USA) i.m., 14 days apart starting at 35–42 days in milk (DIM). All cows received 75 μg of GnRH (Cystorelin, Merial, Iselin, NJ, USA) i.m. 14 days after the second pre-synchronization injection of PGF2α, followed by a third injection of 25 mg PGF2α i.m. 7 days later. Cows received a second injection of 75 μg of GnRH i.m. 54 h after the third PGF2α, and received timed artificial insemination at the time of the second GnRH injection or 24 h later. Multivariate logistic regression was used to analyze the odds of pregnancy at the first service. Variables included in the model were endometritis status (clinical endometritis, subclinical endometritis and normal), farm (two), presence of corpus luteum (CL, yes or no), timing of second GnRH in relation to AI (0 or 24 h), sire fertility (bulls with greater compared with lesser estimated relative conception rates), parity (primiparous and multiparous) and their interactions. Of all variable included in the model, cows with corpus letuem (OR = 1.83 versus OR = 1.00; P = 0.05) 3 days prior to the scheduled start of Presynch–Ovsynch program and primiparous cows (OR = 1.00 versus OR = 0.55; P = 0.04) had increased odds of becoming pregnant at the first service. No differences were found in the odds of first service pregnancy among clinical, subclinical endometritis and normal cows (P > 0.1). In summary, presence of clinical or subclinical endometritis at the initiation of Presynch–Ovsynch estrous synchronization program does not harm the first service pregnancy rate in dairy cows.