8/ MAY 2019 THE RIDER The Way of Horses: Roundworms


lenge for horse breeders. The 1916 United States Depart-


ment of Agriculture book “Diseases of the Horse” describes how the round- worm affects the growth and health of horses – unthriftiness, diarrhea or con- stipation, colic and respiratory prob- lems. Recommended


By Eleanor Blazer Copyright @ 2018


Roundworms Controlling roundworms (Parascaris spp./ascarids) has been an on-going chal-


treatment Ontario’s Horse


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compounds were tartar emetic, turpen- tine or carbon bisulphid for the removal of the parasite. Foals were treated with a mixture of the chemical of choice and honey which was placed on the back of the tongue twice a week. Older horses were fasted for 18 hours and then ad- ministered the poison with a stomach tube. The toxic chemicals basically caused severe diarrhea and purged the intestinal tract. The book warns that the treatments are dangerous to the horse and can cause death or permanent injury to the kidneys or other organs. Roundworms are primarily a


young horse’s nemesis. The newborn foal is free from parasites, but it doesn’t take long for the youngster to be ex- posed. Ascarid eggs can live for years in


pastures and turnouts on plants, buck- ets, fences and stall walls – just waiting for the exploring foal to find and swal- low. The eggs can also become stuck to the mare’s udder and swallowed when the foal nurses. The eggs travel to the small intes-


tine where they hatch. After hatching, the larvae work through the intestinal wall into the blood stream, reaching the


liver and eventually ending up in the lungs. The larvae are coughed up, swallowed and return to the small in- testine where they complete their life- cycle - maturing into adult egg-laying worms. The new eggs are passed out of the horse in the manure where they wait to be ingested by the next horse. It is estimated the eggs can live for close to 10 years in a suitable environ- ment. Extreme heat and cold does not effectively kill the eggs, which are en- cased in a hard protective capsule. As the 1916 book stated round-


worms can cause poor growth, cough- ing, nasal discharge, inflammation and colic. But foal owners must realize that youngsters without symptoms will still have roundworms. Total eradication of roundworms in the environment is im- possible. Over the last 100 years our choice


of chemicals and administration has improved but the effectiveness of our modern dewormers is decreasing. A study done in September 2002


on a farm in Ontario, Canada showed that foals which had been regularly de- wormed with ivermectin since birth had poor roundworm control – they were resistant to ivermectin. [Patrick D Hearn, F & Peregrine, Andrew. (2003). Identification of foals infected with Parascaris equorum apparently resistant to ivermectin. Journal of the American Veterinary Medical Association. 223. 482-5,


455. 10.2460/javma.2003.223.482.] To prevent resistance to deworm-


ers the American Association of Equine Practitioneers recommends for foals and weanlings: “During the first year of life foals should receive a minimum of four anthelmintic treatments. First de- worming should be carried out at about 2-3 months of age, and a benzimidazole drug is recommended to ensure effi- cacy against ascarids. Second deworm- ing is recommended just before weaning (approximately 4-6 months of age). An extra treatment can be justi- fied before weaning if the time period between the two treatments exceeds 3 months. At weaning a fecal egg count is recommended to determine whether worm burdens are primarily strongyles or ascarids, to facilitate the right choice of drug class. Third and fourth treat- ments should be considered at about 9 and 12 months of age, respectively, and treatment should primarily be targeting strongyles. Tapeworm treatment should be included in the 9-month treatment.” https://aaep.org/sites/default/files/Guid elines/AAEPParasiteControlGuide- lines_0.pdf Dewormers are ineffective on


roundworms until the parasites become adults, so deworming foals before the age of 2 months is not advised. De- worming foals at an early age sets up resistance – resulting in dewormers being ineffective later when they can be of use. Care must be taken when admin- istering the first dose of dewormer. If


the foal has a large worm burden the sudden die-off of adult worms can cause a blockage, resulting in im- paction colic. It should be done under the supervision of a veterinarian. By the time the young horse is two


years old resistance to roundworms has developed. Occasionally adult horses will have a low roundworm burden. In 1916 managing manure was the


key to keeping the exposure down. The book recommended stalls and pastures be cleaned daily and the manure not spread on paddocks where mares and foals were kept. Feed was to be offered off the ground. This is true today - management is


key. Overstocking pastures and turnout areas should be avoided. Isolation of new horses with dubious health history should be implemented until a fecal count can be taken and treatment com- pleted before introduction to the herd. Manure removal and pasture rotation can also help in managing internal par- asites. It is impossible to totally remove


the risk of exposure to roundworms, but it can be decreased.


* Earn Professional Certification as Horse Trainer, Stable Manager or Rid- ing Instructor. All courses are online. Visit www.equinestudiesinstitute.org for information.


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