The effects of endometritis on the establishment of pregnancy in cattle.

Endometritis is common in post partum dairy cows and is associated with impaired reproductive performance reflected in reduced first service conception, reduced hazard of pregnancy over the breeding period and increased risk of reproductive culling. The observed effects may be mediated directly by bacterial products, such as lipopolysaccharide (LPS, endotoxin), or indirectly by inflammatory mediators, such as cytokines, eicosanoids, nitric oxide and oxidative stress affecting sperm, ovarian, uterine and embryonic function. An inflammatory milieu in the uterus has been associated with changes in sperm motility and function as well as increased sperm phagocytosis. Zygotes resulting from fertilisation of oocytes with sperm subjected to oxidative stress are less likely to develop to the blastocyst stage. In addition, LPS and tumour necrosis factor-α (TNFα) impair follicular steroidogenesis, growth and ovulation. Oocytes exposed to LPS or prostaglandin (PG) F(2α) during maturation are less likely to develop to blastocyst stage after fertilisation. Embryos exposed to inflammatory mediators during development have fewer trophoectoderm cells. Nitric oxide impairs development of preimplantation embryos and TNFα increases blastomere apoptosis. Endometritis in women has been associated with higher rates of implantation failure. Extragenital inflammation (e.g. mastitis) is also associated with an increased rate of embryonic loss in cattle. These observations make it clear that direct and indirect effects of endometritis, and inflammation in general, can interrupt successful reproduction at several crucial stages.