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Worms – A Pain in the Gut

Worms – A Pain in the Gut. Alison Moore DVM, DVSc, DACVIM National Equine Medical Consultant IDEXX Canada/Vita-Tech Markham, Ontario. Why talk about internal parasites?. Diseases caused by parasites are on the increase There is resistance to dewormers.

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Worms – A Pain in the Gut

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  1. Worms – A Pain in the Gut Alison Moore DVM, DVSc, DACVIM National Equine Medical Consultant IDEXX Canada/Vita-Tech Markham, Ontario

  2. Why talk about internal parasites? • Diseases caused by parasites are on the increase • There is resistance to dewormers

  3. Diseases Caused by Internal Parasites • 3 major groups of intestinal parasites • Roundworms (Parascaris equorum) • Strongyles (Large strongyles –Bloodworms, small strongyles) • Tapeworms • Each causes it own clinical signs that affect performance • Signs are due to migration of larvae • Subclinical signs – poor absorption of feed and supplements

  4. Roundworms • Young horses < 2yrs of age (< 6months of age are most susceptible) • Pot-belly • Poor hair coat • Lethargy • Coughing /lung inflammation • Colic (impactions, intussusceptions)

  5. Deworming: The Philosophy Ascarids

  6. Roundworms • Takes 70 days before eggs are seen in manure • Start deworming at 6 – 8 weeks of age • Develop immunity with age • Eggs survive in environment for years

  7. Bloodworms – Large Strongyles • Strongylus vulgaris • “verminous arteritis” “thromboembolic colic” • Poor-doer • Weight loss

  8. Bloodworms • After ingestion, larvae penetrate the lining of the small intestine by 7 days post-infection • Penetrate the arteries of the cecum and colon and migrate to the root of the mesenteric artery • Develop for 3-4 months then return to the colon • May take 6 to 11 months from ingestion to passing eggs in manure

  9. Cyathastomes – small strongyles • Don’t migrate through body • Infected larvae are ingested and can develop to shedding adults in 6 – 14 weeks or can “hibernate for the winter” or “summer” depending on climate • Form cysts in the lining of the large colon – safe from dewormers-can encyst for 2 years • Difficult to detect in manure

  10. Cyathastomes • Emergence of the hibernating larvae occurs in the spring in the north and fall in the south – very large numbers • 12-30°C (25°C optimum for emergence) • Severe protein losing life-threatening diarrhea • Chronic weight loss, poor digestion, low protein

  11. Tapeworms • Ingest a mite found on the pasture or in the stable that is infected with eggs • Larvae attach at the connection of the small intestine and cecum (valve) • Colic

  12. Tapeworms • Mite activity is temperature dependent – increase in cold dry climate • Affects all ages (weanling and older) • No acquired resistance • Only 30-50% of tapeworm infected horses are positive on examination of the manure • Serum Antibody test becoming available

  13. Diagnosis of Parasites • Fecal floatation • Fecal Egg Count • Serum Antibody Test (Tapeworms)

  14. Fecal Egg Count • Fecal exam only detects eggs from adult females • Eggs per gram of manure • 200 or less EPG is a light load – may not need to deworm (<100 for a foal) • A parasite-free horse is an anomaly and not a realistic goal • Provides vital information about the individual as well as the parasite status of the herd

  15. Fecal Egg Counts • 20% of the horses shed 80% of the worms

  16. Fecal Egg Count Reduction Test • Perform a fecal egg count before administering dewormer then repeat in 14 days • EPG (pretreatment)-EPG (posttreatment)/ EPG (pretreatment) x 100 = FECR • Should be >90% - if not, there is resistance developing

  17. Dewormers • 3 major chemical classes of dewormers: • Macrocyclic lactone (Ivermectin (Eqvalan) moxidectin (Quest) • Benzimidazole (fenbendazole (Panacur) • Pyrantels (Pyrantel Pamoate (Strongid – P) Pyrantel Tartrate (Strongid –T)

  18. Resistance to Dewormers • The persistence of benzimidazole-resistant cyathostomes on horse farms in Ontario over 10 years and the effectiveness of ivermectin and moxidectin against these resistant strains.Can Vet J. 2008 Jan;49(1):56-60. • Macrocyclic lactone-resistant Parascaris equorum on stud farms in Canada and effectiveness of fenbendazole and pyrantel pamoate. Vet Parasitol. 2007 Apr 30;145(3-4):371-6. Epub 2006 Sep 7.

  19. Resistance to Dewormers • 21 countries report resistance to benzimidazoles (Panacur) • Pyrantel resistance is most prevalent in the US (especially to Strongid C) • The more often a horse is dewormed the greater the chance for resistance • Frequent rotation may speed the development of resistance as each generation of worms is exposed to several different classes of drug

  20. Assessing your horse’s risk for parasite burden • Age, health status • Stable or pasture • Stocking density • Travel to other climates • Pasture management • Deworming practices

  21. Dewormers and parasite group • Roundworms – Treated with ivermectin (Eqvalan), moxidectin (Quest), Fenbendazole (Panacur) or Pyrantel Pamoate (Strongid P) • Resistance reported to: ivermectin and moxidectin in Ontario

  22. Roundworms • Goal is to reduce to spread of eggs in the manure • Deworm starting at 6 weeks and then two months later – asses with a fecal egg count in two months • Monitor with fecal egg counts – presence of large numbers of eggs 2 to 4 weeks after treatment suggests the deworming is ineffective

  23. Tapeworms • Treatment with praziquantel (combined with ivermectin or moxidectin in Eqvalan Gold or EquiMax, Quest Plus) or double dose pyrantel pamoate (Strongid P) • Spring and/or Autumn to correspond to exposure to infected mites • Serum antibody test

  24. Strongyles • Large Strongyles – adult stages –can use all class of dewormers, larvae (moxidectin, ivermectin or fenbendazole (twice dose for 5 days) • Small strongles – very susceptible to resistance

  25. Small Strongyles (Cyathostomes) • Fecal egg count on individuals • Low contaminators – deworm twice yearly at beginning and end of grazing season • High contaminators – focus of control program – need treatment throughout grazing season – resistance reported to pyrantel tartrate (Strongid C) and Pyrantel pamoate (Strongid P) • Ivermectin, moxidectin for adults and L4 larvae and Moxidectin for the hibernating stage • Deworm after the fall freeze with Moxidectin or Ivermectin • If travelling to Florida, remember the pastures may be heavily contaminated in the fall and winter

  26. Deworming Summary • Roundworms – at 6-8 weeks every two months – use FEC/RT to determine if resistance (to ivermectin/moxidectin) • Tapeworms – Spring and Fall with Praziquantel combo (Eqvalan Gold) or double dose Strongid P • Large Strongyles – twice yearly with any dewormer – check with FEC • Small Strongyles (Cyathastomes) – After fall freeze with Moxidectin/Ivermectin and again in the spring – monitor with FEC

  27. Manure Management • Only about 5-10% of the parasites are in the horse • The remaining 90-95% are on the ground • Need to reduce contamination by removing manure (vacuuming) if stocking density is high • Compost

  28. Summary • Parasites can cause debilitating disease • Resistance to dewormers is a problem (Quest, Ivermectin, Panacur, Strongid on some farms) • Utilize Fecal egg counts to determine low and high shedders • Use Fecal egg count reduction test to determine resistance to dewormers • Manure and pasture management

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