Equine Health Update Issue 2 Volume 19 - Page 26

EQUINE | Equine Disease Update warranted by a specific diagnosis. Death due to disease or dysfunction of the cardiovas- cular system may be somewhat unexpected. However, after delving more deeply into necropsy records, a not- so-surprising story emerged. Uterine artery rupture was responsible for approximately half of the cases where the main cause of death was attributed to the cardiovas- cular system. This statistic appears to be associated with the presence of numerous breeding farms in Central Kentucky. Increased risk of uterine artery rupture is an important issue for owners and veterinarians worldwide to consider when breeding mares over fifteen years of age. Additionally, the potential high risk for uterine ar- tery rupture in older mares may highlight the option of embryo transfers to surrogate mares to obtain offspring from highly valued aged mares. As with any medical procedure however, embryo transfer and surrogacy are not without risk and may be restricted by certain breed registries. While the main causes of death identified in this pre- liminary review for horses over the age of fifteen in Ken- tucky certainly highlight potential problem areas for the medical management of older horses, a more extensive review of past cases is needed to fully establish signifi- cant trends from this study. Contact: Ashton B. Miller, Graduate Research Assistant, in collaboration with Alan Loynachan, DVM, PhD and Amanda Adams, PhD ashton.miller@uky.edu (859) 257- 4757 Maxwell H. Gluck Equine Research Center Univer- sity of Kentucky Lexington, KY KENTUCKY Parasite Control: An Update Internal parasites of horses have been recognized for centuries. Until the early 1900s, methods for the control of equine endoparasites lacked a scientific basis. For 26 example, in the 1600s one recommendation was to in- cise the horse’s palate with the intent that the ingested blood would kill any internal parasites. Beginning in the 1940s and extending to the 1980s, new classes of anti- parasitic compounds were developed approximately every 10 years. Currently in the USA, only benzimid- azoles (fenbendazole and oxibendazole), tetrahydropy- rimidines (pyrantel pamoate and pyrantel tartrate), and macrocyclic lactones (ivermectin and moxidectin alone or combined with praziquantel) are commercially avail- able for parasite control in horses. The major endoparasites of horses include bots, large strongyles, small strongyles or cyathostomes, ascarids, and tapeworms. Large strongyles (Strongylus spp.) are one of the most significant equine parasites. The larval stages can cause disease due to migration in blood ves- sels and abdominal organs. Drug resistance is not evi- dent in the case of large strongyles. Cyathostome larvae do not migrate parenterally like Strongylus spp., but en- cyst in the mucosa and submucosa of the large intestine of the horse. Intestinal disease can be induced by cya- thostomes when large numbers of larvae excyst from the lining of the large intestine, a condition called “larval cyathostomiasis.” Resistance to fenbendazole, oxibenda- zole and pyrantel pamoate is now common among cya- thostomes. Also, both ivermectin and moxidectin have become less effective against immature (L4) cyathos- tomes in the lumen of the large intestine; thus the life cycle is shortened. Heavy infections with adult ascarids (Parascaris spp.) can cause intestinal blockage and rup- ture because of their bulk. These too have become resis- tant to ivermectin, moxidectin, and pyrantel pamoate. The final group of equine endoparasites, tapeworms (Anoplocephala spp.), can also result in intestinal hyper- trophy, blockage, intussusception, and rupture; they do not exhibit drug resistance. Parasite treatment schedules have been based on the life cycle of the parasites since the early 1900s. In the • Equine Health Update •