Persistent Breeding-Induced Endometritis after Hysteroscopic Insemination in the Mare

Low-dose insemination has been proposed to reduce persistent breeding-induced endometritis (PBIE) in mares with delayed uterine clearance (DUC). Others proposed that hysteroscopic insemination induces an exaggerated inflammatory response and should be avoided in DUC mares. The objectives here were to evaluate presence and severity of PBIE in normal and DUC mares after hysteroscopic insemination with fresh semen, and to determine if hysteroscopy could be used in DUC mares without inducing excessive inflammation. Reproductively normal (n=4) and DUC (n=5) mares received four treatments in random order: uterine body insemination (UB, 1×10 9 spermatozoa, 20ml), hysteroscopic insemination (HYST, 5×10 6 spermatozoa, 0.5ml), sham hysteroscopic insemination (SHAM, semen extender, 0.5ml) and hysteroscopic infusion of seminal plasma (SP, 0.5ml). Significantly more DUC (50%) mares than normal (14%) mares accumulated intrauterine fluid 24h post-treatment. The difference in fluid accumulation between DUC (40%) mares and normal (7%) mares was also significant 48h post-treatment. Fluid scores were not significantly different between treatments in normal mares. However, treatments HYST and SHAM resulted in significantly higher fluid scores 24h but not 48h post-treatment in DUC mares. There was no effect of treatment or mare group on the percentage and total number of neutrophils in uterine fluid 48h post-treatment. Percentage of neutrophils was correlated with duration of hysteroscopy in normal mares, with procedures lasting ≥9min associated with PBIE. There was no effect of mare group, treatment or duration of hysteroscopy on pregnancy rate. Hysteroscopy induces a transient inflammation that is not more severe than that after conventional artificial insemination, suggesting no contraindication to its use in DUC mares.