Wild horse populations in south-east Australia have a high prevalence of Strongylus vulgaris and may act as a reservoir of infection for domestic horses

Abstract

Australia has over 400,000 wild horses, the largest wild equid population in the world, scattered across a range of different habitats. We hypothesised that wild horse populations unexposed to anthelmintics would have a high prevalence of Strongylus vulgaris infections. Verminous endarteritis and colic due to migrating S. vulgaris larvae is now absent or unreported in domestic horses in Australia, yet wild horses may pose a risk for its re-emergence. A total of 289 faecal egg counts (FECs) were performed across six remote wild horse populations in south-east Australia, of varying densities, herd sizes and habitats. Total strongyle egg counts ranged from 50 to 3740 eggs per gram (EPG, mean 1443) and 89% (257/289) of faecal samples had > 500 EPG, classifying them as ‘high level shedders’. There were significant differences in mean total strongyle FECs between different locations, habitats and population densities. Occurrence of S. vulgaris was not predictable based on FECs of total strongyle eggs or small (<90 μm) strongyle eggs. A high prevalence of S. vulgaris DNA in faecal samples was demonstrated across all six populations, with an overall predicted prevalence of 96.7%. This finding is important, because of the ample opportunity for transmission to domestic horses. The high prevalence of S. vulgaris suggests vigilance is required when adopting wild horses, or when domestic horses graze in environments inhabited by wild horses. Appropriate veterinary advise is required to minimize disease risk due to S. vulgaris . Monitoring horses for S. vulgaris using larval culture or qPCR remains prudent. Gastrointestinal parasites in wild horse populations may also serve as parasite refugia, thus contributing to integrated parasite management when facing emerging anthelmintic resistance.

A Ten-Stage Protocol for Assessing the Welfare of Individual Non-Captive Wild Animals: Free-Roaming Horses (Equus Ferus Caballus) as an Example

“…Consequently, such indices may provide information about future welfare risks, and thus become important welfare alerting indices. Some other animal-based indices, such as faecal egg counts (FECs), may also only provide welfare alerting rather than welfare status information (Figure 5b, Table 2), because, when FEC is high, free-roaming horses frequently do not exhibit overt clinical signs of disease [118,119]. Hence, interpreted in isolation they do not necessarily indicate presence of intestinal pathology and any related negative experience.…”

“…Hence, interpreted in isolation they do not necessarily indicate presence of intestinal pathology and any related negative experience. [118]. However, faecal egg counts (FEC) give no indication of the severity of any associated pathology and cannot be used directly to make inferences about the animals' mental experience.…”

Gastrointestinal helminths detected in wild horses in Konya Province, Turkey

“…Additionally, wild horses, which continuously cause environmental contamination due to parasitic scattering, are a constant source of infection for domestic horses [25]. The risk of helminth infections of domestic horses increases due to the capture and redomestication of wild horses and common use of pastures with wild horses.…”

“…The number of studies on gastrointestinal parasites of wild horses is insufficient worldwide. Many helminths, especially S. vulgaris, have been detected in the studies performed [16,25,[29][30][31][32][33][34][35]. The presence of strongyle eggs and some other helminth infections in wild horses has been reported in the USA [29,35], Canada [34], Australia [25], Venezuela [32], Ukraine [30], and Poland [31,33].…”

Welfare of Free-Roaming Horses: 70 Years of Experience with Konik Polski Breeding in Poland

“…Frequent histopathological changes in feral horses' hooves observed in post mortem studies indicate that the feral horse foot type cannot be used as a model for the domestic horse foot [41,80]. Another health-related issue in free-roaming horses is parasite infections [82][83][84][85][86][87][88][89][90][91][92][93][94]. In most studies, the body condition of feral horses was not related to the level of infestation [85], although this was not a rule [86,87].…”