Observed and expected combined effects of clinical mastitis and low body condition on pregnancy loss in dairy cows.

The objective was to compare the observed and expected combined effects of clinical mastitis before timed artificial insemination (TAI) and low body condition at 70 d postpartum (dpp) on pregnancy loss in dairy cows. Cows were examined for pregnancy by ultrasonographic examination 28-32 d after TAI; the presence of an embryo with a heartbeat was the criterion used to determine pregnancy. Cows diagnosed pregnant were re-examined by transrectal palpation of the uterus and its contents 28 d later to confirm pregnancy status and to identify pregnancy loss. Eighty-eight (17%) of 512 cows were diagnosed with pregnancy loss. Cows affected with clinical mastitis before insemination and a body condition score (BCS)≤2.75 at 70 dpp were 2.03 times more likely to experience pregnancy loss, compared to cows without clinical mastitis and with a BCS>2.75 (RR=2.03; 95% CI=1.15, 3.60; P=0.01). This observed combined effect for pregnancy loss (RR=2.03) was higher than the expected combined effect based on adding (RR=1.39) or multiplying (RR=1.42) absolute independent excesses due to clinical mastitis or low body condition.