The interaction between seminal plasma, sperm, and endometrium in inter- and intra-species breeding in equids

Anecdotal experience suggests horse mares have less post-breeding inflammation and better fertility when bred with donkeys. This study aimed to compare the post-breeding inflammatory response of mares exposed to donkey and horse semen and seminal plasma and evaluate the proteome and metabolome of donkey and horse sperm and seminal plasma. Uterine edema, intrauterine fluid accumulation, PMNs on cytology, and concentrations of progesterone, and pro- and anti-inflammatory cytokines (IL1, IL1, IL4, IL6, CXCL8, IL10) concentrations were assessed pre-and post-infusion of semen and seminal plasma (donkey and horse). The metabolome and proteome were analyzed by LC-MS/MS. Mare cycles bred with horse semen had a greater progesterone concentration than those cycles bred with donkey semen at 8 days post-ovulation (P=0.046). At 6 h post-infusion, the inflammatory response due to the donkey semen tended to be lower (P=0.074). Donkey seminal plasma had anti-inflammatory properties compared to horse semen and seminal plasma, as determined by fewer neutrophils on uterine cytology (P<0.05). Horse semen induced resulted in a greater concentrations of IL6 and lesser concentrations of IL1 (P<0.05). Concentrations of PGE1, PGE3, and lactoferrin PGE1, PGE3, and lactoferrin concentrations were significantly more abundant in donkey sperm and seminal plasma. Prostaglandins play an important role in immunomodulation and might contribute to the response triggered in inter-species breeding. In conclusion, breeding horse mares with donkey semen induces a similar post-breeding endometritis to horse semen. Donkey seminal plasma results in a lower post-infusion inflammatory response than other combinations in the immediate post-breeding.