119 The effect of parasitic load on the equine microbiome, hematological parameters, and overall body condition

Abstract

Strongyles are nematode parasites that affect the large intestine and cecum of the horse, with symptoms ranging from loss of condition to colic. Thirty horses from the University of Connecticut campus were used to study the effect of gastrointestinal strongyles on the equine gut microbiome, immune response, body condition, and skin and hair coat conditions. This study included young (n = 16) and adult (n = 14) horses each fall and spring from Fall 2020 to Spring 2022, with young horses 1 to 5 years old and adult horses 6 to 19 years old. Fecal flotation analysis was performed at the beginning of each fall and spring season to classify horses as susceptible to parasites if they had 300 or more strongyle eggs per gram (EPG) or resistant to parasites if they had less than 300 strongyle EPG. Fecal and blood samples were collected each fall and spring to assess gut microbial composition, complete cell counts, and differential cell counts. Body condition scores and body weights were assessed twice per season. Dermatological conditions were recorded once monthly. A split plot design with age as the main effect and fecal egg count (FEC) as the split plot effect was used. Adult and young horses that were susceptible to parasites had significantly increased percentages oflymphocytes and neutrophils and decreased percentages of monocytes and eosinophils compared with horses that were resistant to parasites in Fall 2021 and Spring 2022 (P < 0.05). In adult horses, linear correlation analysis revealed that as parasite load increased, body weight decreased (r = −0.29) and complete cell count decreased (r = −0.29), although these trends were not observed in young horses. Ten percent of the variation seen in microbial community structure was due to phenotype. Linear correlation analysis revealed some changes in skin and hair condition, such as an increase in skin moistness (r = 0.32), tailhead moistness (r = 0.36), and hair thickness (r = 0.44) as parasite load increased and a decrease in hair luster (r = −0.32) as parasite load increased. The effects of strongyle infection on dermatology are still unclear as some of the effects seen contradict previous literature and warrant further investigation. Strongyle load may affect body weight in adult horses. Strongyle infection may affect immune response, but have a minimal effect on microbial composition.