Internal Parasites: Strategies for Effective Parasite Control
Internal parasites, or worms, can be silent thieves and killers. They can cause extensive internal damage without you even realizing your animals are heavily infected. The effects of internal parasites on a horse range from a dull haircoat and unthriftiness to colic and death. Internal parasites lower the horse's resistance to infection, rob the horse of valuable nutrients, and in some cases, cause permanent damage to the internal organs.
In terms of management priorities, establishing an effective parasite control program is probably second only to supplying the horse with clean, plentiful water and high-quality feed. It's that important!
SIGNS OF PARASITISM
Contrary to popular belief, horses can have large numbers of internal parasites while still appearing to be relatively healthy. But in some individuals, especially young horses, parasites can take a visible toll. Common signs of parasitism include the following:
- Dull, rough haircoat
- Lethargy (decreased energy) or depression
- Decreased stamina
- Unthriftiness or loss of condition
- Slowed growth in young horses
- Pot belly (especially in young horses)
- Colic
- Diarrhea
FECAL EGG COUNTS
One of the most useful tools in a parasite control program is the fecal egg count—microscopic examination of fresh manure for parasite eggs. This simple test allows the veterinarian to determine which parasites are present and whether the infection is light, moderate, or heavy. This information is important in developing a deworming program for your horse or farm. Furthermore, egg counts are very important in monitoring the effectiveness of the program, where samples are analyzed both before and after deworming a group of horses.
Fecal egg count involves collecting two or three fresh manure balls from the horse to be tested and sending the manure sample to a veterinary laboratory. Results are expressed as eggs per gram (epg) of manure. A fecal egg count of less than 200 epg suggests a light parasite load. Horses with high fecal egg counts of 500-1000 epg suggest the interval between deworming is too long.
It is important to note that a negative fecal examination does not mean the horse is free of internal parasites. Some types of parasites produce eggs only intermittently. Larvae do not produce eggs at all, and may be present in large numbers in a horse with a fecal egg count of zero. And tapeworm eggs may be missed with routine fecal egg count techniques. The results are most useful when several horses on a farm are tested on the same day. This information gives the veterinarian and farm manager a good idea of the level of parasitism on the property.
DESIGNING A DEWORMING PROGRAM
There is no single deworming program that suits all horses and all situations. The ideal program for your horse(s) depends on number and ages of the horses on your farm, pasture management and your geographic location. It is best to have your veterinarian help you devise an appropriate deworming program for your horse or farm.
Monitoring
Having your veterinarian perform fecal egg counts to determine the amount of egg shedding that your horse has is important. This information will help ensure that the dewormers that are being used are effective and also help determine the frequency of deworming necessary to keep your horse healthy. The outlay of time and money will be well worth it.
A COMPLETE MANAGEMENT PROGRAM
Chemical control using dewormers is just one part of a complete parasite control plan. As parasites are primarily transferred through manure, good management is essential. Some of the procedures listed below can be helpful in reducing parasite burdens:
- Keep the number of horses per acre to a minimum to prevent overgrazing and reduce pasture contamination with parasite eggs and larvae
- Pick up and dispose of manure regularly (at least twice a week during the warmer seasons, even in dirt or sand yards)
- Do not spread manure on fields to be grazed by horses; instead, compost it in a pile away from the pasture before spreading it out
- Mow and harrow pastures periodically to break up manure piles and expose parasite larvae to the elements (larvae can survive freezing, but they cannot tolerate extreme heat and drying for very long)
- Consider rotating pastures by allowing sheep or cattle to graze them, thereby interrupting the life cycles of equine parasites
- Use a feeder for hay and grain rather than feeding on the ground
- Remove bot eggs regularly from the horse's haircoat (flea combs work well in some instances)
- Consult your veterinarian to set up an effective deworming program for your horse(s) and monitor its effectiveness.
