Based on AAEP Parasite Control Guidelines

Equine Parasite Control

Based on AAEP Parasite Control Guidelines

Introduction

Monthly deworming of horses for parasite control is a method developed more than 40 years ago when Strongylus vulgaris (the large strongyle) was the most prevalent parasite type found in the equine gut. However, times have changed and small strongyles are more prevalent in adults while roundworms (Parascaris spp.) remain more prevalent in foals and weanlings. Resistance against dewormers (anthelmentics) is common in small strongyles and roundworms. Adult horses vary greatly in their susceptibility to parasitic infection and in their level of egg shedding. All these things must be incorporated together in order to find the best deworming program for your horse.

Goals of Parasite Control

The goal of parasite control is NOT to get rid of all parasites but to limit parasite infections so animals remain healthy and clinical illness does not develop. Not only is eradication impossible, but it will also lead to development of drug resistance, which is an increasing concern. Treatments are only necessary when the environmental conditions are conducive to egg and larval development and survival. Adverse environmental conditions such as hot summers will rapidly kill developing parasites on pasture.

Strategic Deworming

All horses should receive one or two deworming treatments per year to target large strongyles, tapeworms, pinworms, bots, and nematodes which are responsible for causing summer sores. Deworming treatments should be given during seasons of peak shedding (usually spring and fall). Administration of ivermectin (Zimectrin) in the fall and moxidectin + praziquantel (Quest Plus) in the spring as well as one fecal egg count per year is adequate for most adult horses in this area. All further treatments should target horses that are moderate- high egg shedders.

Fecal Egg counts

Fecal samples may be obtained within 6 hours and should be immediately refrigerated. Refrigerated samples can be tested up to 7 days later. Fecal samples should be obtained 16 weeks after moxidectin administration, 12 weeks after ivermectin administration, and 9 weeks after pyrantel administration.

Classification / Fecal Egg Count
low / 0-200 eggs/gram
moderate / 200-500 eggs/gram
high / >500 eggs per gram

Environmental Control

Some environmental control strategies exist for controlling parasite burden on pastures. Composting will obtain high enough temperatures to eliminate parasites from manure. Non-composted manure should not be spread on pastures. Rotating animals from pasture to pasture and allowing the pasture to be rested for weeks in the summer and up to six months during winter months can decrease the parasite burden. Additionally, allowing livestock to graze on “rested” pasture can also decrease parasite burdens.