The objective of this field trial was to compare the effect of intrauterine (i.u.)
antibiotic or intramuscular (i.m.)
prostaglandin F2 alpha (
PGF2 alpha) 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 > 7.5 cm, 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 500 mg of
cephapirin benzathine intrauterine (i.u.), 500 micrograms 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. There was no benefit of treatment of
endometritis before 4 wk postpartum. Administration of
PGF2 alpha between 20 and 26 DIM to cows with
endometritis that did not have a palpable corpus luteum was associated with a significant reduction in pregnancy rate. Between 27 and 33 DIM, cows with
endometritis treated with
cephapirin i.u. had a significantly shorter time to pregnancy than untreated cows (hazard ratio = 1.63). In this time period, there was no difference in pregnancy rate between
PGF2 alpha and untreated cows, but the difference in pregnancy rate between cows treated with
cephapirin i.u. and with
PGF2 alpha was not statistically significant. Treatment of postpartum
endometritis should be reserved for cases diagnosed after 26 DIM, based on criteria that are associated with subsequent pregnancy rate.