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December 31st, 2018

Horsemen’s Laboratory,

John Byrd D.V.M.

Tel: 217-586-2004

Photos are available on request.

Media Contact:

Tel 607-434-4470

By Nikki Alvin-Smith

Thankfully scientists produced anthelmintic treatment for the equine large stronglye worm in the 1960’s and with the advent of Ivermectin, the presence of the equine large strongyle worm population was fairly well ‘knocked on the head’. There has however, been evidence that suggests the large strongyle worm is showing resistance to certain dewormers. For this reason a targeted deworming program is essential to help ensure a sustainable and effective management protocol for internal equine parasites.

The large strongyle worm enjoys a life cycle that includes migration through various tissues. There are several species of large strongyles but the most pathogenic in horses of all parasites is the Strongylus vulgaris. After ingestion of this nematode’s larvae by the horse grazing at pasture, this parasite will take a journey from the mucosal layer of the horse’s gut via blood vessels to the root of the mesenteric artery and beyond. They have even been found in horses at the root of the aorta, renal, iliac and celiac arteries.

These nefarious worms leave tracks in their wake as they continue their migration during their lifecycle. Eventually returning to the alimentary canal to molt out as adult worms as nodules in the large intestine, and they sit in the lumen for six weeks before the females will lay their eggs. This entire process can take up to 6-7 months.

Anecdotal evidence suggests that a heavy parasitic infection by the large strongyle worm may be responsible for colic and present other major health issues for the horse. Blood clots (embolisms), inflammation of the arteries that damages the blood vessel walls and reduces blood flow to organs have long been blamed on the large strongyle worm’s presence, especially when found in large numbers within foals or adult horses at the roots of arteries.

The obstruction of the blood supply to an organ or region of tissue, typically by a thrombus or embolus, can cause local death of the tissue. This is called infarction and may result in the need for colic surgery. At a minimum the dead tissue may inhibit the peristaltic action of the gut and cause pain, while infarcted areas of the bowel may cause colic that despite surgical resection offers a survival rate of only 10% according to scientific study.

Additional inflammation may occur during this nematode’s life cycle when they migrate in their later stage to the large intestine. Here the tissue that lines the inner wall of the abdomen and covers and supports most of the abdominal organs may also become inflamed, a condition called peritonitis.

So indeed the large strongyle worm in particular S. vulgaris, can be cause for concern if the horse is heavily infected. Deworming of a heavily infected horse should be approached with caution, as the death of the worms may cause further blockages where they have gathered in the arterioles.

How do you know if your horse is infected? The equine fecal egg count test (F.E.C.T.) can identify strongyle worm eggs but cannot differentiate between the small and large strongyle. The treatment for both types is the same so the worm egg count is a valuable tool that can reveal evidence of infection and the need to administer a dewormer.

Consultation should be made with a qualified vet in regard to the type of dewormer that should be used and the schedule necessary for retesting for fecal egg worm count to ensure a 90% expected reduction in egg count numbers. This is especially important if a high rate of infection is suspected. If your retest reveals that the expected egg count reduction as not been attained, it is prudent to consult with an equine parasitology specialist for further treatment advice and for suggestions on more advanced methods of testing.

PLEASE NOTE: This article is available for use in its entirety without edit or excerpt, in any media format on condition that credit is given to Horsemen’s Laboratory, and author Nikki Alvin-Smith as a byline at the beginning of the article publication. Horsemen’s Laboratory URL address and Nikki Alvin-Smith URL must be included. We would appreciate notification of any publication via email to media contact Thank-you for sharing!

This article is brought to you courtesy of Horsemen’s Laboratory Inc., Mahomet, IL. –

About Horsemen’s Laboratory: Established in 1993 by John Byrd D.V.M., an experienced lifelong horseman and a graduate of the University of Illinois College of Veterinary Medicine. As an equine medicine practitioner in California for 13 years, Dr. Byrd served as ex-officio member of the board of directors of the Pacific Coast Quarter Horse Racing Association where he also served as the organization’s official sales veterinarian. In addition, Dr. Byrd frequently officiated, as veterinarian for horse shows sponsored by the management of Orange County Fairgrounds in Costa Mesa, California. Dr. Byrd’s extensive experience with horses led him to observe how a horse’s health could impact performance leading to the founding of the specialist lab for equine fecal worm egg counts. Please visit to find out more about F.E.C.T. services available directly to the horse owner including; advice on equine fecal egg count testing; quick and easy purchase of test kits online; reporting and expert consultation services. Dr. Byrd enjoys sharing his wealth of knowledge of equine parasitology with horse owners from all walks of life, and is available to provide lectures/symposiums for your club, organization or event. Please contact Dr. Byrd via his website for rates and further information.

About Nikki Alvin-Smith: International and national published freelance writer and photographer in such world renowned publications such as The Chronicle of the Horse, Horse and Hound, Dressage and CT, Warmbloods Today, The Horseman’s Yankee Pedlar, Reiter, The Equine Journal, Spur, Hoofprints, Horsin’ Around, Horses All, Field & Stream, Western Horse and Gun, Pony Quarterly, Horses All Canada, Catskill Horse to name a few. Ghostwriting, blog services, PR/Marketing copy either direct with manufacturer or for agencies, copy editing and editor services also available. Nikki also produces catalog copy, white papers, e-books, corporate brochures and advertising copy for international corporations and PR/Marketing for celebrities.

As a Brit who has called the America home for the past 34 years, Nikki brings a unique perspective to the equestrian world. Nikki is also an accomplished Grand Prix dressage trainer/competitor, competing at international Grand Prix level to scores over 72% and is a highly sought clinician offering clinics worldwide. She has been a horse breeder/importer of warmblood and Baroque breeds for more than 25 years. Together with her husband Paul who is also a Grand Prix trainer, they run a private dressage breeding operation and training yard in the beautiful Catskill Mountains of New York. Please visit to learn more about the affordable freelance writing services on offer.

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