Postpartum endometrial cytology in beef cows.

The objectives were to characterize postpartum endometrial cytology and to determine the prevalence of subclinical endometrial inflammation and its impact on reproduction in beef cows. Samples for endometrial cytology (low-volume uterine lavage) were obtained from 135 of 137 Angus cows (2-87d postpartum) in northern Minnesota, 26d before breeding started. Agreement between examiners for subjective inflammation scores was very high (kappa=0.971); the correlation between these scores and PMN counts was high (r=0.83; P<0.001), validating subjective categorization. The proportion of PMN and large mononuclear cells (principally macrophages) declined with postpartum interval (P<0.001), whereas small mononuclear cells were consistently present (and not significantly affected by postpartum interval). Pregnancy rate to fixed-time AI was 29% and overall pregnancy rate was 89%. There was no association between cell type and ultimate pregnancy status or day of conception (P>0.10). Although inflammation later in the postpartum period apparently impaired subsequent reproduction in dairy cows, in cows >50 d postpartum at sample collection in the present study, no cytological parameter significantly predicted final pregnancy status or day of conception. Previous twinning increased the risk of subclinical endometritis (P=0.02), but not the probability of becoming pregnant (P=0.14). In conclusion, we inferred that beef cows had the ability to clear uterine inflammation after resumption of ovarian cyclicity.