Prevalence of large endoparasites at necropsy in horses infected with Population B small strongyles in a herd established in Kentucky in 1966.

This research study involved the post-mortem examination of two horse herds in Kentucky, that had been infected since 1966 with certain parasites that were resistant to standard treatments. The goal was to count and identify larger endoparasites present at the time of death, providing insights into the prevalence and impact of various parasites on these horses.

Study Sample and Context

• Two closed herds of horses, referred to as Old Lot 4 and Field 24, served as the subjects of the study. These horses had been infected with a type of parasite known as Population B small strongyles since 1966, which were resistant to thiabendazole and phenothiazine treatments.
• The study was carried out during February, March, and May of 2005, upon termination of these herds. The horses varied in age, with the youngest being 239 days and the oldest 23 years in Old Lot 4 herd, and from 3 to 20 years in the Field 24 herd.

Procedure and Results

• The necropsy, a post-mortem examination carried out on the horses, focused on identifying and counting large endoparasites. This did not include any content of small endoparasites that may have been present.
• Various types of large endoparasites were identified across the necropsied horses. All 16 horses showed the presence of Gasterophilus intestinalis, a type of botfly. In addition, a smaller number also had another type of botfly called Gasterophilus nasalis.
• Parascaris equorum, a roundworm prevalent in young horses, was found in four horses, while Strongylus vulgaris, a type of strongyles (bloodworms), appeared in the large intestine and cranial mesenteric artery of many horses. Another type of strongyles, Strongylus edentatus was present in several horses as well.
• A high prevalence of Anoplocephala perfoliata, a common tapeworm, was found in all the horses. A smaller number of horses also showed the presence of Oxyuris equi (pinworms) and Thelazia lacrymalis (eye worms).

Significance of the Study

• This study provides insights into the prevalence of various large endoparasites in horse herds where certain parasites are resistant to medications. The data gathered could help in understanding the impact of these parasitic infections on the health of horses and assist in creating better prevention and treatment strategies.