# Horse deworming schedule: fecal egg counts and targeted control > Why fixed rotation deworming schedules fell out of favor, how fecal egg counts sort horses into low, moderate and high shedders, what foals need, and what record to keep for your vet. Canonical: https://lucernel.com/guides/horse-deworming-schedule Last updated: 2026-10-02 Type: Guide. Publisher: Lucernel. ## Short answer The AAEP guidelines have replaced the fixed rotation, where every horse is dewormed every few months, with targeted control. Every adult horse still gets a baseline of one or two dewormings a year, and a fecal egg count shows your vet which horses need more: only the high shedders. Foals follow their own plan, and on most farms tapeworm treatment is at least once a year, in autumn. Your veterinarian sets the schedule and the product. - **Choose this if:** Read on for why the calendar changed and what to ask your vet about egg counts, foals and tapeworms. - **Choose the other option if:** Trotley helps once the plan exists: it records each treatment and test result with the horse, and keeps the dates in one place for the next vet visit. ## Side by side | | Fixed rotation | Targeted control | | --- | --- | --- | | Treats every horse on the calendar | Yes, all horses at set intervals | No, all adults get a baseline once or twice a year; extra treatment follows the egg count and your vet’s advice | | Uses fecal egg counts | No | Yes, to sort low, moderate and high shedders | | Helps slow drug resistance | No, interval programs contributed to resistance | Yes, it aims to leave some worms unexposed to the drug | | Aimed at the few high shedders | No, the same treatment goes to all | Yes, 15 to 30% of horses carry large burdens and shed about 80% of eggs | | Needs a record | Partly, dates of treatment | Yes, dates, product, egg count and test results | ## Why rotation schedules fell out of favor A 2014 review in Equine Veterinary Journal says nematode control has traditionally followed interval treatment regimens, with every horse given an anthelmintic at regular intervals. Those programs sharply reduced disease from large strongyles, but the authors say they made major contributions to anthelmintic resistance, especially in cyathostomins, the small strongyles. Resistance to two of the three drug classes is widespread. The Merck Veterinary Manual puts it plainly: recommendations for equine parasite control have moved away from traditional prophylactic treatments that often followed a rotational schedule to surveillance-based approaches. They consider the parasites present, their resistance profile and local climate, and are summarized in the AAEP Internal Parasite Control Guidelines. The manual also notes that parasitism is a normal state in healthy horses. ## Fecal egg counts and the shedder groups A 2023 paper from Cornell University summarizes the AAEP approach. Horses that shed 0 to 200 eggs per gram of feces are low shedders, 201 to 500 are moderate and more than 500 are high. The paper says 50 to 75% of adult horses in a herd are low shedders, and that only 15 to 30% carry large burdens and shed about 80% of the eggs on pasture. The AAEP key messages, revised in May 2024, set the plan: deworm all horses at a baseline rate of once or twice a year, and target selected horses more often based on the egg count, meaning the high strongyle shedders. For mature horses the full guidelines list one or two macrocyclic lactone treatments a year as the baseline, with praziquantel for tapeworms at least once a year if the horses graze green pasture. Any further treatment goes to horses above 500 eggs per gram, in the transmission season. A low shedder is therefore not left untreated; it gets the baseline and no extra rounds. The Cornell paper’s abstract says low shedders are left untreated; the AAEP’s own guidelines, which this page follows, give them the baseline. The same paper says no fecal egg count technique has been identified as a gold standard and that no two tests have similar diagnostic performance. Our advice: use one lab or one clinic for every count, and ask your vet what to do with a moderate result, since that is a judgment call. A count is a snapshot; the Merck manual adds that egg counts cannot diagnose Strongylus vulgaris, which causes disease through migrating larvae, nor the larval cyathostominosis that occurs when many larvae emerge from the gut wall. ## Foals and young horses Foals get their own plan. The Merck manual says ascarid burdens peak when foals are about 5 months old, after which immunity begins to clear the infection, and that current recommendations call for targeting ascarids twice before weaning, at about 2 and 5 months of age. Ascarids can cause small intestinal impactions in young horses, which need emergency care. The owner-facing Merck chapter describes starting treatment at about 8 weeks and repeating it at 6- to 8-week intervals until a yearling. The two Merck pages differ, which is another reason the plan for a foal should come from your vet, who knows your farm. ## Tapeworm and bots timing, as vets set it For tapeworms, the Merck manual says current recommendations on most farms are to treat at least once a year, in autumn, with more frequent treatment justified by high infection pressure or tapeworm-associated colic on the farm. Tapeworm eggs do not always show up in a fecal sample, so multiple samples or an antibody test may be needed. For bots, the owner chapter says your veterinarian will recommend a treatment program based on your local environment and bot fly season. ## Pasture, manure and the record to keep Merck notes that removing feces from paddocks and pastures aids control and may reduce the number of treatments needed, and that fecal exams are used to check whether a deworming protocol still works. A 2018 survey of 28 Kentucky farms found that despite the AAEP advice, only 17 of 160 horses had a fecal egg count and 65 were dewormed in rotation. The record to keep, which is our own suggestion: the date and product of every treatment, each egg count with the lab and date, the horse’s age and weight, the pasture or group it lives with, and any change in condition. A record like that lets your vet judge whether a product is still working and whether one horse keeps coming back as a high shedder. ## When to call the vet Call your vet for weight loss, loss of condition, diarrhea or repeated colic. Merck lists these as signs of heavier infections, and recurring colic as more likely with tapeworms. In foals, call quickly for colic, since ascarid impactions in young horses need emergency treatment. Do not buy and give dewormers on a guess. Resistance, drug choice and timing need a vet’s judgment, so doses are a question for your vet. Disclosure: Trotley is made by Lucernel, the publisher of this article. ## Frequently asked questions ### How often should I deworm my horse? Not on a fixed rotation. The AAEP says every adult horse gets a baseline of one or two dewormings a year, and the horses that test as high shedders get extra treatment in the transmission season. Your vet sets the timing and the product. ### What is a fecal egg count? A lab count of parasite eggs per gram of feces. The AAEP groups horses as low (0 to 200), moderate (201 to 500) or high (over 500) shedders. ### Is a four times a year deworming schedule still recommended? Fixed interval schedules have fallen out of favor because they contributed to drug resistance. Current guidelines are surveillance-based, so ask your vet which horses need treatment and when. ### When do foals need deworming? Merck’s professional manual recommends targeting ascarids twice before weaning, at about 2 and 5 months. Your vet may set a different plan for your farm. ### Is Trotley available? See the official app page for current availability and pricing. ## Our pick: Trotley, every treatment and result with the horse A targeted plan depends on records: what was given, when, and what the last egg count showed. Trotley keeps each horse’s care events, including medication and veterinary visits, with the lab report stored as a document, shows what is due on a stable calendar with reminders, and exports a PDF or CSV report for the vet. It does not choose a dewormer or tell you when to treat; that stays with your veterinarian. - Medication and vet events logged per horse - Papers and photos stored with the horse - PDF report for the vet or a new owner [See how Trotley works](https://lucernel.com/apps/trotley) ## Sources (checked 2026-10-02) - [AAEP: Internal Parasite Control Guidelines (key messages, revised May 2024)](https://aaep.org/guidelines/parasite-control-guidelines/) - [Merck Veterinary Manual (owners): Gastrointestinal parasites of horses](https://www.merckvetmanual.com/horse-owners/digestive-disorders-of-horses/gastrointestinal-parasites-of-horses) - [Merck Veterinary Manual (professional): Overview of gastrointestinal parasites of horses](https://www.merckvetmanual.com/digestive-system/gastrointestinal-parasites-of-horses/overview-of-gastrointestinal-parasites-of-horses) - [Merck Veterinary Manual (professional): Diseases resulting from gastrointestinal parasites in horses](https://www.merckvetmanual.com/digestive-system/gastrointestinal-parasites-of-horses/diseases-resulting-from-gastrointestinal-parasites-in-horses) - [Equine Vet J (2014): Faecal worm egg count analysis for targeting anthelmintic treatment in horses (PubMed)](https://pubmed.ncbi.nlm.nih.gov/24131301/) - [Pathogens (2023): Evaluation of fecal egg count tests for effective control of equine intestinal strongyles (PMC)](https://pmc.ncbi.nlm.nih.gov/articles/PMC10674696/) - [Vet Parasitol Reg Stud Reports (2018): Management practices associated with strongylid parasite prevalence on horse farms in rural Kentucky (PubMed)](https://pubmed.ncbi.nlm.nih.gov/31014733/)