Determination of optimal diagnostic criteria for purulent vaginal discharge and cytological endometritis in dairy cows

The objectives of this observational study were to identify the optimal diagnostic criteria for purulent vaginal discharge (PVD) and cytological endometritis (ENDO) using vaginal discharge, endometrial cytology, and leukocyte esterase (LE) tests, and to quantify their effect on subsequent reproductive performance. Data generated from 1,099 untreated Holstein cows (28 herds) enrolled in a randomized clinical trial were used in this study. Cows were examined at 35 (±7) d in milk for PVD using vaginal discharge scoring and for ENDO using endometrial cytology and LE testing. Optimal combinations of diagnostic criteria were determined based on the lowest Akaike information criterion (AIC) to predict pregnancy status at first service. Once identified, these criteria were used to quantify the effect of PVD and ENDO on pregnancy risk at first service and on pregnancy hazard until 200 d in milk (survival analysis). Predicting ability of these diagnostic criteria was determined using area under the curve (AUC) values. The prevalence of PVD and ENDO was calculated as well as the agreement between endometrial cytology and LE. The optimal diagnostic criteria (lowest AIC) identified in this study were purulent vaginal discharge or worse (≥4), ≥6% polymorphonuclear leukocytes (PMNL) by endometrial cytology, and small amounts of leukocytes or worse (≥1) by LE testing. When using the combination of vaginal discharge and PMNL percentage as diagnostic tools (n = 1,099), the prevalences of PVD and ENDO were 17.1 and 36.2%, respectively. When using the combination of vaginal discharge and LE (n = 915), the prevalences of PVD and ENDO were 17.1 and 48.4%. The optimal strategies for predicting pregnancy status at first service were the use of LE only (AUC = 0.578) and PMNL percentage only (AUC = 0.575). Cows affected by PVD and ENDO had 0.36 and 0.32 times the odds, respectively, of being pregnant at first service when using PMNL percentage compared with that of unaffected cows; odds ratios were 0.33 and 0.69 for PVD and ENDO, respectively, when LE was used. Kappa value (agreement) of the pairwise comparison for the PMNL percentage and LE was 0.43. Vaginal discharge, endometrial cytology, and LE can be used to diagnose PVD and ENDO, and to predict pregnancy status at first service. The use of LE could be a good alternative to endometrial cytology for on-farm testing.