For young horses aged 12-24 months of age, small redworm, ascarid and tapeworm remain the parasites of concern. This age group is one of the most vulnerable to parasite-associated diseases, so control programmes for youngstock need to be especially rigorous.
Regular worm egg counts to determine the predominant type of parasite infection are important, particularly as a second wave of ascarid infection is known to occur in some yearlings.
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, yearlings 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.). Fastidious paddock management is especially important for pastures being grazed by broodmares, foals or yearlings. Grazing rotation for animals in this age group is strongly advised so they don’t remain on the same pasture for successive years.
Testing protocol for equine yearlings 12-24 months old
12-24 months
- Perform worm egg count reduction tests
- Tapeworm test (using the EquiSal saliva or blood serum antibody ELISA test providing they are no longer suckling). If either indicate significant tapeworm infection, or disease is present, a ‘Proudman’ faecal flotation worm egg count should be carried out, followed by appropriate treatment and 14 days later, a second ‘Proudman’ faecal flotation worm egg count reduction test to determine whether the treatment has been effective.
- Annual larval culture for large redworm
Treatment protocol for equine yearlings 12-24 months old
- Ascarid only: Treat with fenbendazole or pyrantel.
- Strongyles only: >200 epg. ivermectin or pyrantel if efficacy is indicated by worm egg count reduction test.
- Both ascarid and cyathostomins: 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 yearlings 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.
Yearlings in the late autumn/winter
All yearlings that have grazed over the summer, are recommended a routine larvicidal treatment for the possibility of encysted stages of small redworm. 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 yearlings 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).
Updated Summer 2026 following release of CANTER Guidelines Chapter 11