After the first 6-7 months of age, alongside ascarid infections, cyathostomin and tapeworm infections start to increase. Tapeworms can establish at 5-6 months of age, and positive ELISAs may be seen at this time. Animals of all ages are at high risk of acquiring these parasites and developing associated disease.
All horses under the age of five are automatically classed as High Risk using the CANTER Risk Profile Tool. However, within this age bracket, some fall into a critical-risk category. These include ultra-vulnerable animals living on stud farms with high stocking densities and poor pasture management.
Conversely, weanlings on premises with small numbers and good pasture management represent a baseline-risk; they remain in the high-risk bracket by default of their age but are significantly less vulnerable to disease. Decisions on how to apply the below approach will rely on the risk factors of the weanlings.
Every effort should be made to reduce the overall risk by optimising non-chemical parasite control methods (i.e. poo-picking, low stocking densities, resting pastures, co-grazing with ruminants, etc.). Recently weaned foals and yearlings should always be turned out onto ‘clean’ grazing with the lowest possible levels of parasite contamination because animals of this age group are at high risk of developing parasite-associated disease.
Testing protocol for equine weanlings 7-11 months old
Worm egg count every 8 weeks to determine the predominant parasite type present to inform wormer choice
Worm egg count reduction test recommended to monitor treatment efficacy
Larval culture for large redworm
Treatment protocol for equine weanlings 7-11 months old
- Ascarid only: treat with fenbendazole or pyrantel, alternating treatment where previous worm egg count reduction tests indicate both chemicals are effective.
- Redworm only: < 200 epg. no treatment is required. Strongyle egg count > 200 epg. administer an ivermectin Alternatively, pyrantel (or fenbendazole) if efficacy is indicated by previous worm egg count reduction test.
- Ascarid and strongyles: Fenbendazole/pyrantel followed by a worm egg count reduction test. Depending on the resistance profile, weanlings may have to be treated by two different drug classes, i.e., fenbendazole or pyrantel for ascarids and ivermectin for adult small redworm. However, a pyrantel or fenbendazole could be effective against both parasite categories, if verified by worm egg count reduction test.
Particularly for weanlings in the critical-risk category, results should be considered alongside weight, growth and overall health indicators with your prescriber. Treat those that need it, aiming to leave some (at least 10% of the herd if possible) untreated for refugia. For targeting adult stages of small redworm a pyrantel or an ivermectin is preferred. If using moxidectin – check data sheet regarding minimum age.
Weanlings in the late autumn/winter
In the UK, many foals will be weaned in the autumn/early winter, a time when a larvicidal treatment for the possibility of encysted stages of small redworm may be considered. All weanlings that have grazed over the summer, are recommended a routine dose. A five-day course of fenbendazole would be appropriate if results of previous worm egg count reduction tests identify susceptibility of these parasites to this drug; alternatively, moxidectin (or a moxidectin-praziquantel if tapeworm treatment is also indicated) may be considered, providing the young horse has a good covering of body fat.
The small redworm blood test is not usually indicated for horses in this age group.
For weanlings in the critical-risk category, consider a second dose of a larvicidal wormer in the back half of the winter, if egg shedding on worm egg count results remains high. We recommend alternating chemicals (if previous worm egg count reduction tests indicate efficacy of both licenced larvicidals).
Large Redworm
Although the prevalence of large redworm (is currently low in the UK, reductions in the overall use of anthelmintics based on targeted and diagnostic-led treatments might potentially increase the risk and incidence of this parasite. Youngstock may be particularly at risk due to their higher susceptibility. Monitoring for these parasites by larval culturing should be considered. (CANTER Guidelines (Second Edition). 2026)
Updated Summer 2026 following release of CANTER Guidelines Chapter 11