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WORMING-what every horse owner needs to know.

WORMING-what every horse owner needs to know. Feel free to share

A very dear friend of mine administered a routine wormer to her horse, using a standard equine wormer that she bought from a local saddlery, and 2 days later her horse was dead from the effects of parasitic colitis.

It was a tragedy that nobody could have foretold, and I was devastated to hear of this heartbreaking loss of her beloved equine friend.

So much so that it sat badly with me for many years to come. And as time went on I would come into contact with other horse owners, situated all over the world, who had also wormed their horses and it had led to a fatal spasmodic colic episode where their horse had also died.

My gut instinct kept telling me that something was wrong surrounding these occurrences, and I just could not get my mind to quieten over this terrible series of situations involving wormers and colic, as with every case I heard my alarm bells grew louder and louder.

Which fuelled me more into further research and I investigated in more detail what could be going wrong for wormers to be causing these fatal colic events for our equine friends .....

In my bid for answers, I went to the experts in the field and read articles and researched papers, as well as spoke to many different Parasitologists, to try to glean as much information as possible about why this could be happening.

And what I found out goes against everything we have all come to believe is true about horse wormers.....

So here goes with the ugly truth about the how’s, why’s, and when’s relating to horse wormers.

Firstly, how we test for worms needs to change because faecal egg counts do not pick up the most dangerous types of horse worms, which are the real killers ....and are called ENCYSTED STRONGYLES.

Now I want to repeat that faecal egg counts DO NOT DETECT ENCYSTED STRONGYLE WORM LARVAE.

Yet it is these nasty little bleeders that are the reason horses die when traditional wormers are used as they go on to cause parasitic colitis.


Because although there are many different types of worms to address in horses, these Cyathostomes in their immature form can add up to millions of larva that bury (encyst) deep into the lining of the intestines and stomach in our horses and can sit there for sometimes years, waiting for the right time to come forth.

And guess what happens when you use a standard wormer- that due to the removal of the other horse worms created by using a normal wormer, a huge vacancy occurs inside the horse's body that triggers these horrible little demons to come forth en masse.

When this happens a mass of endotoxins are released, and it’s due to this mass invasion that effectively poisons your horse, causing severe spasmodic colic to occur which can go on to kill the horse directly or through forced euthanasia due to the extreme pain and discomfort.

What is shocking is that the folks who study horse worms are already well aware of this, and time and time again the Professionals in this field confirmed that only 1 type of chemical wormer could address these encysted strongyles, and that was MOXIDECTIN.

Understandably, the more I learned about this, the more upset I became. As to think the world has lost so many horses to this awful situation and yet these worm companies continue to mislead the horse-loving public with names that suggest their wormers will kill all worms, such as "broad-spectrum wormers" when they most definitely do not, is a very hard pill to swallow. 

As I still see in nearly every tack and grain score this false claim on too many worming products to list here.

But then this is sadly what I’ve discovered in so many other areas of the horse, after all of my year's researching, is that it is rarely about the horse in the billion-dollar equine industry but more so about the mighty dollar, and companies will tell you anything you want to hear to sell you their carefully marketed products purely to make money. 

With the monitoring of such false claims largely goes unpoliced when it’s about animals.

So, moving forward what can you do to protect your horse from worms and the effects of a standard wormer .....

Thankfully it is easy to get it right by the use of a moxidectin based wormer to address as well as prevent worms, as it’s these combination wormers with Moxidectin that have BEEN PROVEN to kill ALL types of worms, including these offending encysted strongyles.

Another alternative to use is what Vets refer to as a “Panacur Bomb”- but it is hard on the horse as it eradicated the all-important stomach biome. However, it has saved horses- and this is to administer a vet recommended dose of Panacur worming paste for 5 days running.

I personally would use this method in an emergency to save a horse but feel that it’s too harsh on the digestive system to use regularly as a routine worming program.

As much as I hate chemical wormers, unfortunately, there is no other type than wormers other than those that contain moxidectin that can address this situation or the dreaded “Panacur Bomb”.

Therefore we can highly recommend (in New Zealand) the wormers called Equest Plus or Ultra-Mox to be used twice a year as a routine way to protect against worms, or more if worms are suspected.

Plus we strongly recommend NOT to use other types of wormers that don’t contain Moxidectin, as despite what the name suggests or the packets may claim, they could cause more harm than good.

Due to this, the old ways of wormer rotation have also not been found to help address all types of worms either so rotation is also not recommended.

Also for anyone out there who is using natural wormers - firstly as much as it pains me to say this as I normally support wholeheartedly a natural approach, sadly homoeopathic and herbal remedies do not work to address these worms in our research. And our own tests have seen little to no effect in using them as a defence against any worms but especially not in Encysted Strongyle/Small Strongyles/Cyathostomes.

As for Diatomaceous Earth. Whilst it has been found to offer a broad spectrum mineral base and is good for supplements, I’m afraid we have also found in our research that unfortunately it doesn’t work on internal parasites, and any claims for it to do so are unproven. Once inside the body, the product is no longer dry, therefore its parasite shredding properties cease to exist.

To be clear and transparent - we are a horse rescue centre and I carried out this research for our own knowledge and the needs of the horses at our centre, to make sure we were using the best worming approach to help the rescue horses in our care. Therefore we are completely independent and have no agenda, purpose or association with any of the worming companies or products mentioned in this article.

Our sole purpose to recommend the mentioned products is to prevent more horses from suffering due to the misleading info on wormers and because of the research carried out, along with guidance from parasitologists.... and also because they have been proven to work.

Please Note: Moxidectin should not be used with underweight horses or foals under 4 months- please only use it as stated on the packet. If in doubt consult your vet. If you are located somewhere else other than New Zealand, we highly recommend finding a moxidectin based wormer which we have found is available in most countries.

Our own worming program involves a manure management program in addition to worming twice per year using the moxidectin based wormers, in August at the start of spring and again in autumn. As well as worming all new horses upon arrival, we have been very happy with the positive results from this approach.

I sincerely hope this prevents the needless deaths of any more horses.

Dedicated to all the beloved horses taken way too soon due to man's greed.


Corning, S. (2009) Equine cyathostomins: a review of biology, clinical significance and therapy

Parasites & Vectors. 2(Suppl 2):S1

Jasko, D.J., Roth, L. (1984) Granulomatous colitis associated with small strongyle larvae in a horse. J Am Vet Med Assoc. 185(5): 553-4

Love, S. (1992) Parasite-associated equine diarrhea. Compend Contin Educ Pract Vet. 14: 642–649

Mair, T.S. (1993) Recurrent diarrhea in aged ponies associated with larval cyathostomiasis. EVJ 25(2):161-3

Mair, T.S. (2002) Larval cyathostomosis. 432-436. In. Manual of Equine Gastroenterology.

Eds Mair, T.S., Divers, T., Ducharme, N. WB Saunders. Edinburgh, UK

Lyons E, Tolliver S, Drudge J: Historical perspective of cyathostomes: prevalence, treatment and control programs. Vet Parasitol. 1999, 85: 97-112. 10.1016/S0304-4017(99)00091-6.CAS, Google Scholar

Smets K, Shaw D, Deprez D, Vercruysse J: Diagnosis of larval cyathostominosis in Belgium. Vet Rec. 1999, 144: 665-668.CAS, Google Scholar

Mfitilodze M, Hutchinson G: Prevalence and abundance of equine strongyles (Nematoda: Strongyloidea) in tropical Australia. J Parasitol. 1990, 76: 487-494. 10.2307/3282826. Google Scholar

Proudman CJ, Matthews JB: Control of Intestinal Parasites in Horses. In Practice. 2000, 22: 90-97.Article, Google Scholar

Collobert-Laugier C, Hoste H, Sevin C, Dorchies P: Prevalence, abundance and site distribution of equine small strongyles in Normandy, France. Vet Parasitol. 2002, 110: 77-83. 10.1016/S0304-4017(02)00328-X.CAS, Article,PubMed, Google Scholar

Love S, Murphy D, Mellor D: Pathogenicity of cyathostome infection. Vet Parasit. 1999, 85: 113-122. 10.1016/S0304-4017(99)00092-8.CAS, Article, Google Scholar

Souto-Maior M, Alves L, Mota R, Carvalho G, Barbosa C: AAVP Proceedings 45th Annual Meeting. 36-

Herd R: The changing world of worms: The rise of the cyathostomes and the decline of Strongylus vulgaris. The Compendium for Continuing Education of the Practicing Veterinarian - Equine. 1990, 732-736.Google Scholar

Bucknell D, Gasser R, Beveridge I: The prevalence and epidemiology of gastrointestinal parasites of horses in Victoria, Australia. Int J Parasitol. 1995, 25: 711-724. 10.1016/0020-7519(94)00214-9.CAS, Google Scholar

Linc E, Hoglund J, Ljungstrom B, Nilsson O, Uggla A: A field survey on the distribution of strongyle infections of horses in Sweden and factors affecting faecal egg counts. Equine Vet J. 1999, 31: 68-72, Google Scholar

Peregrine A, McEwen B, Bienzle D, Kock T, Weese J: Larval cyathostominosis in horses in Ontario: An emerging disease. Can Vet J. 2006, 47: 80-82.PubMed Central, Google Scholar

Chapman M, French D, Klei T: Gastrointestinal helminths of ponies in Louisiana: A comparison of species currently prevalent with those present 20 years ago. Journal of Parasitology. 2002, 88: 1130-1134. 10.1645/0022-3395(2002)088[1130:GHOPIL]2.0.CO;2.Article, PubMed, Google Scholar

Lyons E, Swerczek T, Tolliver S, Bair H, Drudge J, Ennis L: Prevalence of selected species of internal parasites in equids at necropsy in central Kentucky. Vet Parasitol. 2000, 92: 51-62. 10.1016/S0304-4017(00)00266-1.CAS, Article, PubMed, Google Scholar

Love S, Duncan J: Development of cyathostome infection of helminth naïve foals. Equine Vet J. 1992, 93-98. Suppl 13

Baudena M, Chapman M, French D, Klei T: Seasonal development and survival of equine cyathostome larvae on pasture in south Louisiana. Vet Parasitol. 2000, 88: 51-60. 10.1016/S0304-4017(99)00198-3.CAS, Article, PubMed, Google Scholar

Von Samson-Himmelstjerna G, von Witzendorff C, Sievers G, Schneider T: Comparative use of faecal egg count reduction test, egg hatch assay and beta-tubulin codon 200 genotyping in small strongyles (cyathostominae) before and after benzimidazole treatment. Vet Parasitol. 2002, 108: 227-235. 10.1016/S0304-4017(02)00197-8.CAS, Article, PubMed, Google Scholar

Traversa D, Iorio R, Klei T, Kharchenko V, Gawor J, Otranto D, Sparagno O: New method for simultaneous species-specific identification of equine strongyles (nematode, strongylida) by reverse line blot hybridization. Journal of Clinical Microbiology. 2007, 45: 2937-2942. 10.1128/JCM.00714-07.PubMed Central, CAS, Article, Google Scholar

Dvojnos G, Kharchenko V: Morphology and differential diagnostics of parasitic larvae of some strongylidae nematode of horses. An Parasitol. 1990, 31: 15-28.CAS, Google Scholar

Reinemeyer C, Herd R, Gabel A: Distribution of adult and larval cyathostomes in helminth naïve foals after primary infection. Equine Vet J. 1988, 20 (4): 296-297.CAS, Article, PubMed,Google Scholar

Kuzmina T, Kharchenko V, Starovir A, Dvojnos G: Analysis of the strongylid nematodes (Nematoda: Strongylidae) community after deworming of brood horses in Ukraine. Vet Parasitol. 2005, 131: 283-290. 10.1016/j.vetpar.2005.05.010.CAS, Article, PubMed, Google Scholar

Abbott E: Larval cyathostomosis: The disease, its diagnosis and treatment. Equine Practice. 1998, 20: 6-7.Google Scholar

Giles C, Urquhart K, Longstaffe J: Larval cyathostomiasis (immature trichonema-induced eneteropathy): A report of 15 clinical cases. Equine Vet J. 1985, 17 (3): 196-201., CAS, Article, PubMed, Google Scholar

Matthews A, Morris J: Cyathostomiasis in horses. Vet Rec. 1995, 136 (2): 52-CAS, Article, PubMed, Google Scholar

Reilly G, Cassidy J, Taylor S: Two fatal cases of diarrhea in horses associated with larvae of small strongyles. Vet Rec. 1993, 132 (11): 267-268.Google Scholar

Vitellozzi G, Fioretti D: Gross and histopathological findings in the large intestine of healthy slaughter horses and their correlation with cyathostome infection. Acta Medica Veterinaria. 1991, 37: 159-170.Google Scholar

Chapman M, French D, Taylor H, Klei T: One season of pasture exposure fails to induce a protective resistance to cyathostomes but increases numbers of hypobiotic third-stage larvae. Journal of Parasitology. 2002, 88: 678-683. 10.1645/0022-3395(2002)088[0678:OSOPEF]2.0.CO;2.Google Scholar

Kelly J, Fogarty U: Outbreak of larval cyathostomiasis on a thoroughbred stud farm. Irish Veterinary Journal. 1993, 46: 133-136.Google Scholar

Love S, Mair T, Hillyer M: Chronic diarrhea in adult horses: a review of 51 referenced cases. Vet Record. 1992, 130: 217-219.Google Scholar

Love S, Escala J, Duncan J, McLean J: Studies on the pathogenic effects of experimental cyathostome infections in ponies. Proceedings of Sixth International Conference, Equine Infectious Diseases. 1991, 149-155.Google Scholar

Smets K, Shaw D, Deprez J, Vercruysse J: Diagnosis of larval cyathostominosis in horses in Belgium. Vet Record. 1999, 144: 665-668.Google Scholar

Herd R, Gabel A: Reduced efficacy of anthelmintics in young compared with adult horses. Equine Vet Journal. 1990, 22: 164-169.Google Scholar

Matthee S: Anthelmintic treatment in horses:The extra-label use of products and the danger of under-dosing. J S Afr Vet Assoc. 2003, 74 (2): 53-56.Google Scholar

Paul J: Optimal internal parasite control for horses with emphasis on larval cyathostomosis. Large Animal Practice. 1999, 20: 33-36.Google Scholar

Reinemeyer C: Equine small strongyles: Unanswered questions. The Compendium - Equine Forum. 1992, 816-819.Google Scholar

Heile C, Schein E: parasite control in horses: an overview, Part 1, endoparasites. Praktische Tierartz. 2004, 85J: 890-897.Google Scholar

Herd R: Equine parasite control - problems associated with intensive anthelmintic therapy. Equine Veterinary Education. 1990, 2: 41-47.Google Scholar

Hutchens D, Paul A, DiPietro J: Treatment and control of gastrointestinal parasites. Vet Clin North Am Equine Pract. 15 (3): 561-573.

Uhlinger C: Equine small strongyles: Epidemiology, pathology and control. Compendium on Continuing Education for the Practicing Veterinarian. 1991, 13: 863-Google Scholar

Monahan CJ: Anthelmintic Control Strategies for Horses. Companion and Exotic Animal Parasitology. 2000, International veterinary Information Service, []Google Scholar

Varady M, Konigova A, Corba J: A field study to evaluate the efficacy of fenbendazole on 9 stud farms. Veterinarni Medicina. 2004, 49: 42-46.Google Scholar

Collobert C, Bernard N, Clement F, Hubert J, Kerboeuf D, Flochlay A, Blond Riou F: Efficacy of oral moxidectin gel against benzimidazole-resistant cyathostomes in horses both naturally and artificially infected with a field population. J Equine Vet Science. 1998, 18: 9588-9590.Google Scholar

Eysker M, Boersma , Kooyman F: Effect of repeated oxfendazole treatments on small strongyle infections in Shetland ponies. Res Vet Science. 1989, 46 (3): 409-412.CAS, Google Scholar

Rolfe P, Dawson K: The efficacy of a combination anthelmintic against oxibendazole resistant small strongyles, large strongyles and ascarids in horses. Aust Vet J. 1994, 71: 304-306. 10.1111/j.1751-0813.1994.tb03453.x.Google Scholar

Schillinger D, Hasslinger M: Benzimidazole resistance in small strongyles of horses - occurrence in Germany and strategies for avoiding resistance. Rev Med Vet. 1994, 145: 119-124.Google Scholar

Lloyd S, Smith J, Connon R, Hatcher M, Hedges T, Humphrey D, Jones A: Parasite control methods used by horse owners: Factors predisposing to the development of anthelmintic resistance in nematodes. Vet Record. 2000, 146: 487-492.Google Scholar

Lendal S, Marsen M, Bjorn H, Craven J, Chriel M, Olsen S: A questionnaire survey on nematode control practices on horse farms in Denmark and the existence of risk factors for the development of anthelmintic resistance. Vet Parasitol. 1998, 78: 49-63. 10.1016/S0304-4017(98)00117-4.Google Scholar

Herd R, Majewski G: Comparison of daily and monthly pyrantel treatment in yearling thoroughbreds and the protective effect of strategic medication of mares and their foals. Vet Parasitol. 1994, 55: 93-104. 10.1016/0304-4017(94)90059-0.Google Scholar

Slocombe O, de Gannes R: Cyathostomes in Canada resistant to pyrantel salts and effectively removed by moxidectin. Vet Parasitol. 2006, 140: 181-184. 10.1016/j.vetpar.2006.03.019.Google Scholar

Monahan C, Chapman M, Taylor H, French D, Klei T: Experimental cyathostome challenge of ponies maintained with or without benefit of daily pyrantel tartrate feed additive: Comparison of parasite burdens, immunity and colonic pathology. Vet Parasitol. 1998, 74: 229-241. 10.1016/S0304-4017(97)00095-2.Google Scholar

Monahan C, Chapman M, Taylor H, French D, Klei T: Foals raised on pasture with or without daily pyrantel tartrate feed additive: Comparison of parasite burdens and host responses following experimental challenge with large and small strongyle larvae. Vet Parasitol. 1997, 73: 277-289. 10.1016/S0304-4017(97)00096-4.Google Scholar

Osterman E, Nilsson O, Hoglund J, Uggla A: Treatment intervals for ivermectin and pyrantel: Treatment of strongylids in horses. Svensk Veterinartidning. 1996, 48: 281-284.Google Scholar

Taylor S, Kenny J: Comparison of moxidectin with ivermectin and pyrantel embonate for reduction of faecal egg counts in horses. Vet Record. 1995, 137 (20): 516-518.Google Scholar

Boersma J, Borgsteede F: The prevalence of anthelmintic resistance of horse strongyles in the Netherlands. Veterinary Quarterly. 1991, 13: 209-217.Google Scholar

Fisher M, Jacobs D: Prevalence of benzimidazole resistance in equine cyathostome populations in southeast England. Vet Rec. 1993, 130 (15): 315-318.Google Scholar

Kaplan R: Anthelmintic resistance in nematodes of horses. Vet Research. 2002, 33: 491-507. 10.1051/vetres:2002035.Google Scholar

Reinemeyer C, Farley A: Comparison of cyathostome control and selection for benzimidazole resistance using moxidectin gel or Panacur Powerpac paste. AAVP Proceedings, 47th Annual Meeting. 2002Google Scholar

Eysker M, Boersma J, Kooyman F: The effect of ivermectin treatment against inhibited early third stage, late third stage and fourth stage larvae and adult stages of the cyathostomes in Shetland ponies and spontaneous expulsion of these helminths. Vet Parasitol. 1992, 42: 295-302. 10.1016/0304-4017(92)90071-G.Google Scholar

Xiao L, Herd R: Comparative efficacy of moxidectin and ivermectin against hypobiotic and encysted cyathostomes and other equine parasites. Vet Parasitol. 1994, 53: 83-90. 10.1016/0304-4017(94)90020-5.Google Scholar

Monahan C, Chapman M, Taylor H, French D, Klei T: Comparison of moxidectin oral gel and ivermectin paste against a spectrum of internal parasites of ponies with special attention to encysted cyathostome larvae. Vet Parasitol. 1996, 63: 225-235. 10.1016/0304-4017(95)00910-8. Google Scholar

Bello T, Lanigan J: A controlled trial evaluation of three oral dosages of moxidectin against equine parasites. J Equine Vet Sci. 1994, 4: 483-488. 10.1016/S0737-0806(06)81977-5.Google Scholar

Vercruysse J, Eysker M, Demeulenaere D, Smets K, Dorny P: Persistence of the efficacy of moxidectin gel on the establishment of cyathostominae in horses. Veterinary Record. 1998, 143: 307-309. Google Scholar

Corba J, Praslicka J, Varady M, Andrasko H, Holakovsky P: Efficacy of moxidectin 2% equine gel and EQVALAN 1% paste against parasitic nematodes of horses. Helminthologia. 1995, 32: 215-218. Google Scholar

Costa A, Barbosa O: Comparative efficacy of moxidectin gel and ivermectin paste against parasitic nematodes of horses. Rev Bras Parasitol. 1995, 4: 114. Google Scholar

Costa A, Barbosa O, Moraes F, Acuna A, Rocha U, Soares V: Comparative efficacy evaluation of moxidectin gel and ivermectin paste against internal parasites of equines in Brazil. Vet Parasitol. 1998, 80: 29-36. 10.1016/S0304-4017(98)00186-1.Google Scholar

Jacobs D, Hutchinson M: Equine cyathostome infection: Suppression of faecal egg output with moxidectin. Vet Rec. 1995, 137: 545-CAS Article PubMed Google Scholar

Schumacher J, Taintor J: A review of the use of moxidectin in horses. EquineVet Educ. 2008, 20: 546-551. 10.2746/095777308X356956.Google Scholar

Solari Basano F, Chierichetti N, Genchi C: Use of moxidectin and ivermectin in cyathostominae yearly control plan. Comparison of efficacy and persistency in naturally infected horses. Parassitologia. 1998, 40: 168-Google Scholar

Slocombe O, Lake M: Return of strongyle eggs in feces of equids in Ontario after treatment with moxidectin or ivermectin. Proceedings AAVP. 1996, Abstract #31.Google Scholar

Zeeuw G, Hasslinger M: Vergleichende untersuchungen zu eizahlreduktion und behandlungs - interval bei endo-parasiten des pferdes. Der Praktische Tierarzt. 1997, 78: 857-864.Google Scholar

Eysker M, Boersma J, Kooyman F: Emergence from inhibited development of cyathostome larvae in ponies following failure to remove them by repeated treatments with benzimidazole compounds. Vet Parasitol. 1989, 34: 87-93. 10.1016/0304-4017(89)90168-4.

Steinbach T, Bauer C, Sasse H, Baumgartner W, Rey-Moreno C, Hermosilla C, Damriyasa I, Zahner H: Small strongyle infection: Consequences of larvicidal treatment of horses with fenbendazole and moxidectin. Vet Parasitol. 2006, 139: 115-131. 10.1016/j.vetpar.2006.03.028.Google Scholar