Identification of the optimal diagnostic criteria combination for reproductive tract diseases in dairy cows of 100 days in milk or more

The objective of this study was to determine the optimal diagnostic criteria combination for purulent vaginal discharge (PVD) and endometritis (ENDO) in cows ≥100 DIM to predict the probability of pregnancy. A prospective observational study was conducted in 24 commercial Holstein herds selected by convenience. Cows ≥100 DIM identified as nonpregnant by veterinarians were systematically enrolled in the study and were examined with a Metricheck device (discharge) and a cytobrush device combined with a leukocyte esterase test. No reproductive tract treatments were allowed and cows were systematically enrolled on an ovulation synchronization protocol and inseminated. Data from 1,064 reproductive tract examination events from 918 different Holstein cows were included. Diagnostic criteria combinations of discharge score and esterase score were used to identify PVD and ENDO, respectively. Combinations were compared using mixed logistic regression models accounting for diagnostic criteria (PVD and ENDO), DIM, parity, and season, as well as herd and cow clustering as random effects. The optimal diagnostic criteria combination was chosen based on the variation explained when these thresholds were included in a model (lowest Akaike information criterion; AIC), and their ability to predict pregnancy status (highest area under the receiver operating characteristic curve; AUC). The lowest AIC (1,021) and highest AUC (0.898) were obtained with a combination of a discharge score ≥2 (flecks of pus or worse) for PVD and an esterase score ≥0.5 (trace of leukocytes or worse) for ENDO. Based on these criteria, the proportions of PVD and ENDO were 21.5% and 37.8%, respectively. The overall probability pregnancy at artificial insemination was 30.7%; it was higher in unaffected cows than in cows with reproductive tract diseases. In conclusion, the optimal diagnostic criteria combination for cows ≥100 DIM was a discharge score ≥2 for PVD and a esterase score ≥0.5 for ENDO, and cows with PVD or ENDO had poorer reproductive success than unaffected cows.