Adults and foals are not the same job.

Not a calendar

SVA’s press release of 5 April 2022 is still online. With faecal results, often only half the horses need treatment, sometimes fewer. A spring sample has to be able to find large strongyles and tapeworm, not only eggs of the small strongyles. Resistance is already a problem in small strongyles and in foal ascarids.

Med avmaskning baserad på resultat från träckprover behöver ofta bara hälften av hästarna avmaskas, ibland ännu färre.

The SVA horse-advice page was last reviewed 17 September 2026 and still says the same thing: test first, then treat the horses that are shedding. Its week-by-week foal plan is not copied here.

Adult horses

Strongyles and tapeworm. The test decides who is treated. Interval dosing drove Strongylus vulgaris, and the thromboembolic colic that goes with it, out of well-managed yards. AAEP, Merck and SVA say stop rotational dosing every 6–8 weeks. AAEP’s 2024 text, where it could be retrieved, says do not deworm on fixed intervals year-round, and abandon rotational deworming. Egg-count bands sometimes used in yards (under 200, 200–500, over 500 eggs per gram) are a yard convention, not a law. One to two strategic treatments a year, for parasites an egg count misses, is the evidence brief’s summary of that practice. It is not a calendar this page writes for a named horse.

Foals: ascarids come first

SVA says stud foals should be assumed to meet ascarid infection, and that foal ascarids often resist drugs, especially the ivermectin group used against adult strongyles. An egg count still matters, because it shows which worm is there. AAEP says targeted treatment of foals, weanlings and yearlings based on faecal egg counts is not recommended, while egg counts still matter because ascarids often need a different drug class from strongyles. The count is not a reason to put the foal on the adult horse’s plan, and it is not a reason to rotate the whole yard every six to eight weeks. Your vet writes the foal plan. This page does not.

Removing manure from grass paddocks lowers the infection pressure. It is stable hygiene, not a substitute drug. A faecal egg-count reduction test every few years is how a yard checks whether a drug class still works. A 29-year necropsy series of young horses, which did not open on 6 October 2026, is cited in the evidence brief for a shift: from about 2000, fatal Parascaris and cyathostomin infections replaced S. vulgaris and tapeworm deaths. Larval cyathostominosis still carries a high case fatality when it occurs, often cited as 40–70 percent via Corning 2009 and later reviews.

The 80 percent colic line

D “Some studies show 80 percent of colic cases relate to parasites, with larval strongyles most responsible for colic in adult horses.” That sentence is still on a University of Minnesota Extension page, last modified 2 October 2026. It is not current colic epidemiology. Parasites are one real slice of some colics: tapeworm at the ileocaecal junction, S. vulgaris, larval cyathostominosis. They are not the whole explanation.

Do not

• No dose in milligrams, and no product name.
• Do not give a dog a horse wormer. Horse ivermectin can kill some herding breeds that carry the MDR1 / ABCB1 variant.
• Herbal and “organic” products have not been shown to work as worm control in formal controlled studies, according to the AAEP text reviewed in 2024.

Grades, resistance figures and the link check

Ask your vet.

Sources cited here

• SVA, 5 april 2022, avmaska inte rutinmässigtOpened 6 October 2026. Published 2022-04-05. The line that often only half the horses, sometimes fewer, need treatment is still there.
• SVA, avmaskning av hästOpened 6 October 2026. Last reviewed 17 September 2026, before the cutoff. The week-by-week foal plan and named substances are not copied into the owner pages.
• AAEP internal parasite guidelines PDFDirect GET returned 403, and a later fetch returned 500. One retrieval in the same session returned the text. “Reviewed and updated in 2024”. No text dated after 6 October 2026 was opened. Milligram doses are not repeated.
• Merck Veterinary Manual, parasite control in horsesOpened 6 October 2026. Full review and last updated July 2025, Martin K. Nielsen. Not after the cutoff.
• University of Minnesota Extension, the 80 percent lineOpened 6 October 2026. Last-Modified 2 October 2026. The sentence about 80 percent of colic cases is still there. Grade D. Not current colic epidemiology.