EXPLORING THE IMPACTS OF CLINICAL RESOLUTION OF METRITIS ON DAIRY COWS THROUGH AN EPIDEMIOLOGICAL AND A MOLECULAR LENS

Metritis is a polymicrobial uterine disease defined by the inflammation of all layers of the uterus within 21 days postpartum. Metritis diagnosis is based on the evaluation of vaginal discharge, which is characterized by fetid, watery, and reddish-brown discharge. Metritis is associated with negative impacts on reproduction, milk production, removal from the herd, and cow welfare. Although antimicrobials are widely used to treat cows with metritis, approximately 20% of cows are not cured within two weeks of commencing treatment. Failure to achieve clinical cure has negative effects on performance. Although studies have reported that cows that fail to undergo clinical cure may have a more intense degree of inflammation and tissue damage compared to cows that achieve clinical cure of metritis, the mechanisms that underlie clinical cure failure of metritis remain unclear. The objective in the first study (Ch. 2) was to characterize differences in the uterine and serum metabolome associated with clinical cure failure of metritis in lactating Holstein cows. Differences in the uterine metabolome on day 0 (day of metritis diagnosis) associated with clinical cure failure were linked to carbohydrate, amino acid, and lipid metabolism. Greater concentrations of arachidonic acid, ribose, and glutaric acid were associated with clinical cure failure, suggesting a greater degree of tissue lesion and inflammation. No differences in the serum metabolome were associated with cure failure. No differences in uterine metabolome were associated with clinical cure failure on day 5 (day of cure assessment). The findings suggest that clinical cure failure is associated with a greater uterine inflammatory process that does not continue until cure assessment day. Approximately 50% of the cows treated for metritis are cured within five days after treatment, but the literature regarding the differences in lactational performance associated with time to cure of metritis is scarce. The objective in the second study (Ch.3) was to evaluate the association between time to clinical cure of metritis and reproductive performance, milk production, and removal from the herd. Cows that achieved clinical cure within five days after antimicrobial therapy had improved reproductive performance (risk of receiving a first service and achieving pregnancy by 300 DIM) and a lower risk of removal from the herd compared with those that recovered later. Time to clinical cure of metritis was not associated with differences in total milk production. Time to cure of metritis may be a useful indicator of future performance and survivability in dairy herds and may help guide on-farm decisions and identify cows at greater risk for suboptimal outcomes. Together, these findings advance the understanding of the biological and performance consequences of metritis recovery, offering insights that may guide future research and management strategies to improve reproductive health in dairy herds.