Nemabiome sequencing reveals seasonal and age associated patterns of strongyle infection and high prevalence of Strongylus vulgaris in Alberta feral horses

Abstract

Unmanaged feral horses, naïve to dewormers, offer a unique opportunity to study natural communities of equine parasites. These communities may include parasites that are rare in managed populations, and these may be transmitted to domestic horses in areas where there is contact between feral and domestic equine populations. There have been only a few studies of gastrointestinal parasite populations in horses, and very few from North American equine populations. This study aimed to gain insights into parasite biology through identification of the strongyle parasite species infecting feral horses in Alberta, Canada, and to test for species-specific infection patterns across season and horse age. Fecal samples (N = 149) were collected from unique individuals in the Sundre Equine Management Zone (EMZ), Alberta, across two years: 2021 (N = 62) and 2022 (N = 87). In 2021, samples were collected in summer (N = 31; 8 foals, 5 subadults, 18 adults) and fall (N = 31; 5 foals, 1 subadult, 25 adults). In 2022, samples were collected in spring (N = 36; 4 subadults, 32 adults), summer (N = 41; 4 foals, 8 subadults, 29 adults), and fall (N = 20; 1 foal, 2 subadults, 17 adults). Fecal egg counts showed that these horses shed high numbers of strongyle eggs relative to domestic horse populations (mean = 1337.01 ± 961.81 epg), and nemabiome analyses identified a total of 34 strongyle species. Species richness and aggregate strongyle FECs were highest in subadults and during the summer, while lowest in foals and during the fall. There was a high prevalence of large strongyle species, especially Strongylus vulgaris (85.91 %), with strongyle species-specific prevalence and FECs strongly associated with age and season. Understanding the factors driving species-specific parasite infection provides important information on strongyle parasite ecology and may aid the development of targeted parasite control strategies.

Keywords: Cyathostomins; DNA metabarcoding; Equine; FEC; Parasite ecology.

Graphical abstract

Fig. 1

Age and seasonal variation in strongyle species richness and fecal egg counts from 149 feral horses from the Sundre Equine Management Zone in Alberta, Canada. Foals (N = 18) are 0–1 years old, Subadults (N = 18) are >1–3 years old, and Adults (N = 113) are >3 years old. Sampling occurred across three seasons: Spring (N = 49), Summer (N = 50), and Fall (N = 50).

Fig. 2

The relative abundance of the 34 strongyle species detected in Alberta feral horses across season and horse age. Sample sizes for each category are displayed above each bar.

Fig. 3

Species-specific prevalence of the 15 most common strongyle parasite species by age class modeled in the study. Foals are 0–1 years old (N = 18), Subadults are >1–3 years old (N = 18), and Adults are >3 years old (N = 113). Significant differences are denoted by asterisks: p < 0.05 (∗), p < 0.01 (∗∗), and p < 0.001 (∗∗∗).

Fig. 4

Species-specific fecal egg counts of 15 strongyle species infecting Alberta feral horses by age class. Foals are 0–1years old (N = 18), Subadults are >1–3years old (N = 18) and Adults are >3years old (N = 113). Significant differences are denoted by asterisks: p < 0.05 (∗), p < 0.01 (∗∗), and p < 0.001 (∗∗∗).

Fig. 5

Species-specific fecal egg counts of 15 strongyle species infecting Alberta feral horses grouped by samples collected in Spring (N = 36), Summer (N = 72), and Fall (N = 41). Significant differences are denoted by asterisks: p < 0.05 (∗), p < 0.01 (∗∗), and p < 0.001 (∗∗∗).

Fig. 6

Principal coordinate analysis of the (A, C) Jaccard and (B, D) Bray-Curtis dissimilarity matrices of parasitic strongyle community composition among N = 149 feral horses from the Sundre Equine Management Zone, Alberta, Canada. Points are colored by Age (Foals N = 18; Subadults N = 18; Adults N = 113) or Season (Spring N = 49; Summer N = 50; Fall N = 50). Each point represents a strongyle parasite community.