Age, Donor Status, and Chilled Semen Increase Mare Uterine Inflammation Risk

Persistent breeding-induced endometritis (PBIE) is a significant cause of infertility in mares, characterized by the failure of the uterus to clear inflammation and fluid after breeding. This condition can lead to repeated breeding attempts, increased veterinary costs, and ultimately, a reduced foaling rate. While the general mechanisms of PBIE are understood, the specific predisposing factors in warmblood mares, particularly the interplay of age, embryo donor status, and semen type, have not been comprehensively quantified.

The analysis revealed several significant predisposing factors for PBIE in warmblood mares. Mares aged 15 years or older showed a substantially increased risk, with an incidence rate 2.8-fold higher compared to mares under 10 years of age (p<0.001). Furthermore, mares actively utilized as embryo donors experienced a 45% higher incidence of PBIE than non-donor mares (p=0.003), likely due to repeated uterine manipulations and flushes. Insemination with chilled semen was also identified as a significant risk factor, leading to a 32% increase in PBIE cases compared to fresh semen insemination (p=0.008). The most critical finding was the synergistic effect: mares over 15 years old, used as embryo donors, and inseminated with chilled semen, had an alarming 5.1-fold higher likelihood of developing PBIE compared to young, non-donor mares bred with fresh semen. These factors independently and synergistically contribute to the uterine inflammatory response, hindering successful conception.