Presence of Equine Internal Parasites Based on Post-Mortem Examination

The UK Veterinary Diagnostic Lab looked for three types of equine internal parasites during necropsies.
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Research at the University of Kentucky Veterinary Diagnostic Laboratory looked for the presence of select species of internal parasites in necropsied horses. Thinkstock

Determination of an individual horse’s internal parasite infection is usually based on fecal egg counts of a live horse. However, some parasites are more difficult to identify with microscopic examination of fecal egg counts. 

A study at the University of Kentucky’s Veterinary Diagnostic Laboratory looked at the actual intestinal contents on post-mortem exam of horses [Lyons, E.T.; Bolin, D.C.; Bryant, U.K.; Cassone, L.M.; et al. Postmortem examination (2016–2017) of weanling and older horses for the presence of select species of endoparasites: Gasterophilus spp., Anoplocephala spp. and Strongylus spp. in specific anatomical sites. Veterinary Parasitology: Regional Studies and Reports, 2018]. None of the three parasite species considered in this study have demonstrated dewormer resistance.

A search for Gastrophilus spp. (bots) in the stomach and duodenum was performed in 69 horses. Investigators examined the cecum and terminal ileum of 139 horses for tapeworms (Anoplocephala spp.) and large strongyles species. These horses did not come with any deworming history; however, it was assumed they were well cared for based on their thrifty health without normal signs of internal parasitic infections.

The salient results are as follows:

  • 39% were infected with bots (Gastrophilus spp.)
  • 44% were infected with Anoplocephala perfoliata
  • No Anoplocephala magna were found; they are usually found in the small intestine, but only a small portion of the ileum was examined.
  • Only four of the horses with tapeworm infections had eggs identified on fecal examination.
  • Prevalence of tapeworms is not changed since 40 years ago despite availability of anti-tapeworm medications (praziquantel and pyrantel) possibly because these drugs might not have been used in these horses.
  • Horses aged 16-20 had higher prevalence of tapeworms than other age groups.
  • No large strongyles spp. (S. vulgaris or S. edentatus) was found in the cecum/ileal area of any of the 139 horses’ intestines. However, two horses that evidenced poor care based on hair coat, pot-bellied appearance, and ill thrift had aneurysms of the cranial mesenteric artery that contained adult large strongyles. The authors suggest that large strongyle infections might be present without evidence of clinical parasitic disease.

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