Reproductive and health outcomes of horses affected by focal mucoid placentitis

Focal mucoid (nocardioform) placentitis occurs sporadically worldwide and occasionally has been associated with local epidemics of disease in central Kentucky. Objective was to quantify the effects of focal mucoid placentitis on a farm during spring 2020 outbreak. Outcomes were prospectively identified early in the spring and data were collected in a single cohort of mares during 2020-2021 and on their foals during 2020-2022. Focal mucoid placentitis was diagnosed in 36 of 162 mares; 6 foals died at birth and 30 foals (83%) were viable compared to 119 of 126 viable foals (94%) from normal mares. Foals born to mares with placentitis weighed 10 lb less compared to those from healthy mares, received colostrum that was slightly lower in quality and had ~ 30% lower blood IgG concentrations. However, postnatal foal survival, incidence of infectious or orthopedic foal diseases, sale values, and racing performances were not different between these 2 groups. Focal mucoid placentitis did not recur in subsequent years and the reproductive performance of mares with this form of placentitis was not affected in the subsequent breeding season. Study suggested that although the disease may be underdiagnosed via farm-submitted samples, surviving foals and affected mares were able to overcome the effects of this condition and their performance was comparable to their peers in the absence of additional treatment.