Morphometric Study of Infective Larvae of Cyathostomins of Horses and Their Distribution

Cyathostomins or small strongyles account for more than 50 species of intestinal parasites of horses, and it becomes a challenge to identify these nematodes even at the genus level. Although the available morphological keys consider the number, shape, and arrangement of the intestinal cells of infective larvae (L3) into: types A, B, C, D, E, F, G, H, Gyalocephalus capitatus, and Posteriostomum spp, there are limited scientific reports. The aim of this study was to identify L3s and to determine their frequency and morphometric features from eight horse-breeding farms from two different breeds. Feces from naturally infected adult animals were collected, and the fecal culture was performed using a pool from each location. Optical microscopy was used to identify (n = 400) which type of L3. Another group of larvae (n = 160) were measured using a macroimaging station microscope. The frequency of L3s for types A, B, C, D, E, F, G, H, and G. capitatus were 62, 1.3, 5.7, 25.3, 1.4, 2.3, 0.4, 1.1, and 0.5%, respectively. Cyathostomins type A was the most common larva, followed by type D. The results indicate that Thoroughbred horses have a more heterogeneous parasitic fauna than the Criollo horses. The average size of the larvae was 734.5 μm (±58.3) for type A, 743.3 μm (±49.7) for type C, and 742.5 μm (±48.7) for type D. This study reinforces the importance of identifying and determining the prevalence of cyathostomin infective stage larvae to complement studies on their biology and epidemiology in horses.