Worms in Horses
In our first article we looked at the most common and most common and troublesome parasites in horses. In this article we look at signs of parasitism, fecal egg counts and designing a deworming programme for your horse
Signs of Paratism
Contrary to popular belief, horses can have potentially dangerous 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, and in monitoring the effectiveness of the program.
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. High fecal egg counts of 500—1,000 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.
Dewormers
There are several different dewormers, or anthelmintics, currently available. Most are broad-spectrum, meaning that they are effective against several different types of parasites. It is generally best to use a broad-spectrum dewormer as the basis of your deworming program. If a specific problem is identified, such as tapeworms or encysted small strongyles, a more specific dewormer can be used.
No deworming product is 100 percent effective in ridding every horse of all internal parasites. However, it is not necessary for a product to kill every worm in order to improve the horse’s health, minimize the risk of serious disease, improve feed efficiency and reduce pasture contamination with parasite eggs and larvae.
Treatment interval
It is a good idea to have your veterinarian help you determine the best deworming interval for your horse. Fecal egg counts can be very useful in this regard, as well as in evaluating the effectiveness of the product you’re using.
Rotating products
Whether or not to rotate dewormers (switch to a chemically different product every few months or every year) is a controversial topic. When the same or a chemically similar dewormer is used repeatedly for years, the parasites may become resistant to it and the product then becomes less effective, or even ineffective. However, rotating products too often could create strains of parasites that are resistant to multiple products. Whether or how often to rotate classes of dewormer is something you should discuss with your veterinarian.
Methods of administration
There are three main ways of administering dewormers:
- Oral paste syringe
- Feed additive (powder, liquid or pellets)
- Nasogastric (stomach) tube
All three methods are effective, provided the proper dose is given at the right time, and the horse receives the full dose. The dose must be calculated based on the horse’s body weight. Weight tapes are an accurate enough way of estimating a horse’s body weight for this purpose.
Deworming pastes and feed additives are convenient and easy to administer. However, some horses find them unpalatable and spit them out or refuse to eat them. So be sure that all of the dose you’ve given is actually consumed by the horse.
Tube deworming is a highly effective means of ensuring that the horse receives the proper dose because the dewormer is delivered directly into the horse’s stomach. However, with the range of dewormers now available, it is seldom necessary for a veterinarian to deworm a horse by this method
Designing a Deworming Programme
There are two basic types of deworming programs:
- Interval—deworming at regular intervals of one, two or three months, depending upon the product and the management system
- Strategic—deworming only at certain times of the year or when fecal egg counts rise
Combination programs can also be used. For example, continuous deworming can be supplemented with strategic deworming for bots.
There is no single deworming program that suits all horses and all situations. The ideal program for your horse(s) depends on the type, number and ages of the horses on your farm, pasture management and your geographic location. It is best to have your regular veterinarian help you devise an appropriate deworming program for your horse or farm.
Monitoring
Whichever deworming program or product you use (e.g., monthly, vs. two or three monthly dewormings; single product vs. rotation of products; etc.), have your veterinarian perform fecal egg counts every 6—12 months to make sure your program is effective. The outlay of time and money will be well worth it.
A Complete Management Programme
Chemical control using dewormers is just one part of a complete parasite control plan. As parasites are primarily transferred via manure, good management is essential.
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, 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.
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 lifecycles of equine parasites.
Keep foals and weanlings separate from yearlings and older horses to minimize the foals’ exposure to ascarids and other 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.
© Copyright Bayer AG 2013. Article reproduced with permission from Bayer
