The influence of age and breeding technique on a mare’s susceptibility to persistent breeding-induced endometritis

Abstract

This retrospective study examined factors affecting the susceptibility of mares to persistent breeding-induced endometritis (PBIE). In particular, the differences in susceptibility between young and teenage mares, and between broodmares and embryo donors were investigated, and the efficacy of conventional treatments was assessed. Records were available from mares inseminated at Utrecht University’s Faculty of Veterinary Medicine during 2018-2021, this amounted to 1745 inseminated estrous cycles from 769 different mares. PBIE was defined as the presence of more than 2cm of uterine fluid ≥24 h after insemination. Mares were divided into groups based on age (≤ 6 years; 7-13 years; ≥14 years), breeding system (broodmare/ET donor), reproductive status (maiden, foaling and barren) and semen type (frozen-thawed/fresh-cooled). Additionally, the number of inseminations per cycle, straws per (frozen semen) dose, cycle number, use of estrus or ovulation-inducing agents and the month of insemination were assessed. Subsequently, associations between the incidence of PBIE and pregnancy rates were examined. Overall, per cycle incidence of PBIE was 27.6%. PBIE was most frequent in the oldest mare group (42.3%) and least frequent in the youngest mares (11.2%). The incidence of PBIE was higher in donor mares (35.1%) than in broodmares (22.6%; p<0.05). PBIE was not significantly associated with a reduced pregnancy rate (p=0.24), suggesting that treating susceptible mares with uterine lavage and oxytocin after breeding minimizes the consequences of PBIE on fertility.