Equine abortion is a common and frustrating condition with a variety of infectious and noninfectious causes.
Foal resting in stable near mare
Following changes in the causes of abortion in horses over multiple years may help to elucidate environmental risk factors or changes in disease prevalence over time.
© 2016 by Carien Schippers
Evaluation of the fetoplacental unit can aid in understanding the cause of individual foal loss, allow early detection of infectious causes of abortion, and identify trends over multiple years that can help predict future causes of fetal loss.
Following changes in the causes of abortion over multiple years may help to elucidate environmental risk factors or changes in disease prevalence over time.
Causes of abortion over the last four breeding seasons from 2016 to 2019 General trends in abortion have remained consistent over time, with placentitis being the most commonly diagnosed cause of abortion in all years. Placentitis cases represented 24.6%, 20.2%, 34.5%, and 25% for 2016, 2017, 2018, and 2019.
Typically, non-infectious causes of abortion (umbilical cord torsion, twins, fetal and maternal stress, and abortions of unknown etiology) are more common than infectious causes (viral, bacterial, and fungal infections) with the exception of 2016, which had 145 cases of mucoid (nocardioform) placentitis, increasing the percentage of infectious abortions to 55%.
Evaluation of the last four breeding seasons shows that cases of mucoid placentitis and abortion of undetermined cause have the most variation between years. Abortions due to fungal infection, fetal bacteremia, umbilical cord torsion, and fetal stress have remained fairly stable.
An increase in miscellaneous causes of abortion and undetermined causes occurred in 2018 and 2019. Miscellaneous causes include a variety of conditions including congenital malformations, fetal and maternal stress, cervical pole necrosis, fetal organ necrosis or inflammation, hydrops and Potomac horse fever.
This increase may reflect normal variation between years. Alternatively, monitoring and intervention for early placentitis and vaccination for infectious cases of abortion such as leptospirosis and EHV-1 may be decreasing the incidence of these recognized diseases and result in a corresponding increase in the percentage of cases of abortion without an identified cause.
Abortions of undetermined cause increased each year at 14.9% in 2016, 27.5% and 38.2% in 2017 and 2018 and peaking at 44% in 2019. Continued monitoring of trends will help to determine the significance of these variations.
Press release by Diane Fury article published in Equine Disease Quarterly