Relationship of peripartum inflammation with reproductive health in dairy cows.

Failure of a robust but well-regulated immune response may result in reproductive tract inflammatory disease, such as metritis, purulent vaginal discharge, or endometritis. Metritis is consistently associated with reduced diversity of the uterine microbiome. Similarly, purulent vaginal discharge at 4 to 6 wk postpartum is strongly associated with bacterial infection of the uterus. Conversely, the microbiome of healthy cows and those with subclinical endometritis is generally similar, so endometritis is thought to be a consequence of dysregulation of inflammation rather than changes in uterine microbiota. There is an emerging concept that inflammation is not only a reaction to injury or disease but that it can be a consequence of or precursor to metabolic disturbances. The degree of systemic inflammation is associated with the level of trauma and bacterial contamination of the uterus or mammary gland, the degree of fat mobilization and release of nonesterified fatty acids, and perhaps leaky gut, all of which result in the release of proinflammatory cytokines. Therefore, uterine inflammation may be exacerbated by systemic inflammation, but may also contribute to heightened systemic inflammation in transition cows. However, clarity and progress are limited by a lack of validated criteria to quantify systemic inflammation and to identify its sources.