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The objective of this field trial was to compare the effect of intrauterine (i.u.) antibiotic or intramuscular (i.m.) prostaglandin F_2α (PGF_2α) on time to pregnancy in dairy cows diagnosed with clinical endometritis between 20 and 33 days in milk (DIM). The case definition of endometritis was the presence of purulent uterine discharge or cervical diameter >7.5cm, or the presence of muco-purulent discharge after 26 DIM. There were 316 cows with endometritis from 27 farms assigned randomly within herd to receive 500mg of cephapirin benzathine intrauterine (i.u.), 500μg of cloprostenol i.m., or no treatment. The rate of resolution of clinical signs 14 d after treatment was 77% and was not affected by treatment. Reproductive performance was monitored for a minimum of 7 mo after treatment. Survival analysis (multivariable proportional hazards regression) was used to measure the effect of treatment on time to pregnancy …