A scoping review of the global distribution of causes and syndromes associated with mid-to late-term pregnancy loss in horses between 1960 and 2020

Equine pregnancy loss is frustrating and costly for horse breeders. The reproductive efficiency of mares has significant implications for a breeding operation’s economic success, and widespread losses can have a trickle-down effect on those communities that rely on equine breeding operations. Understanding the causes and risks of equine pregnancy loss is essential for developing prevention and management strategies to reduce the occurrence and impact on the horse breeding industry. This PRISMA-guided scoping review identified 514 records on equine pregnancy loss and described the global spatiotemporal distribution of reported causes and syndromes. The multiple correspondence analysis identified seven clusters that grouped causes, syndromes, locations and pathology. Reasons for clustering should be the focus of future research as they might indicate undescribed risk factors associated with equine pregnancy loss. People engaged in the equine breeding industry work closely with horses and encounter equine bodily fluids, placental membranes, aborted foetuses, and stillborn foals. This close contact increases the risk of zoonotic disease transmission. Based on this review, research is required on equine abortion caused by zoonotic bacteria, including Chlamydia psittaci, Coxiella burnetii and Leptospira spp., because of the severe illness that can occur in people who become infected.