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Internal
parasites are silent killers. They can cause extensive internal damage, and you
may not even realize Your animals are heavily infected. At the very least, parasites
can lower resistance, rob the horse of valuable nutrients, and cause gastrointestinal
irritation and unthriftiness. At their worst, they can lead to colic, intestinal
ruptures, and death. 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! 
IDENTIFYING
THE ENEMY
There are
more than 150 internal parasites that afflict horses, including several major
species. Among the most common and troublesome are:
- Large
strongyles (bloodworms)
- Small
strongyles
- Ascarids
(roundworms)
- Pinworms
- Bots
- Tapeworms
- Threadworms
- Lungworms
Any or
all of these parasites can be present in the horse at one time, but they may
be at different stages in their life cycles. This will influence the deworming
program needed to combat them. Also, keep in mind that some species can lay more
than 200,000 eggs a day, so parasite loads can escalate quickly.
PARASITE DAMAGE
Different
parasites harm the horse in different ways. They can damage tissues and vital
organs, including the major blood vessels to the intestines, lungs, liver, stomach,
and intestines, as they migrate through the horse's system to complete their
life cycles. They can cause obstructions and ulcerations within the horse's digestive
tract, and they can also cause intense irritation as they lay eggs, such as pinworms
do.
SIGNS OF PARASITISM
Contrary
to popular belief, many horses that have dangerous parasite levels appear to
be perfectly healthy. From the outside they may be fat, sleek and shiny, while
on the inside the worms are doing irreparable damage. But in other horses, especially
young horses, parasites can take a visible toll. Signs of infestation might include:
- Dull,
rough haircoat
- Lethargy
or decreased stamina
- Weightless
- Coughing
and /or nasal discharge
- Tail rubbing
and hair loss
- Resistance
to the bit due to mouth lesions
- Colic
- Summer
sores
- Depression
- Loss of
appetite
- Unthriftiness
or loss of condition
- Diarrhea
FECAL
EXAMINATIONS
One of
the most under-utilized tools in an effective parasite control program is the
fecal examination, which merely involves taking two to three fresh fecal balls
to your veterinarian for laboratory analysis. This simple process can identify
the specific parasites infecting a horse.
Rarely
are the worms themselves visible in the manure. But by counting the types and
numbers of parasite eggs present in the fecal sample, your veterinarian can recommend
the right deworming agents to do the job. Fecal eggs per gram counts (EPG) also
tell an owner about the degree of parasite infestation on a farm or within a
herd.
The fecal
exam is a cost-effective follow-up to deworming to determine whether the dewormer
has worked. It's good practice to do a fecal EPG count within two weeks after
deworming 
THE IMPORTANCE OF ROTATING DEWORMING AGENTS
Parasites
can develop resistance to many of the chemicals used to kill them. After a period,
the deworming agents may therefore simply become ineffective. To prevent this,
it's important to rotate classes of drugs used in your program, Be sure that
you don't simply change brand names, however, since many products contain the
same drugs but under different labels. Although some manufacturers claim that
certain products do not require rotation, a good safeguard is to do it anyway.
That way, there's no question about resistance developing.
With opinions
varying as to how often dewormers should be rotated, it is recommended to consult
your veterinarian for guidance. By utilizing broad-spectrum deworming agents
and rotating them as recommended by your veterinarian, you should be able to
rid your horse of most worms.
METHODS
OF ADMINISTRATION
There
are three primary ways of administering dewormers. They are:
- Oral paste
syringe
- Nasogastric
tube (tubing)
- Feed additive
All three
methods are effective. The key is that the deworming product must be given in
the proper dose at the proper time, and that it is fully consumed and retained
by the animal. Deworming pastes and feed formulations have come into widespread
use because of convenience and ease of administration. They are a good choice
as long as the horse ingests the entire dose. (The dose must be calculated based
on the horse's weight.) The problem is that some horses may find them unpalatable
and spit them out.
Tube deworming,
once the method of choice, is still a highly effective means of controlling parasites.
The advantage of administering dewormers via a nasogastric tube is that the veterinarian
can ensure the proper dose is delivered directly to the horse's stomach. The
disadvantage is that it causes the animal temporary discomfort when it is passed
through the nostrils and down the esophagus into the stomach. Because of the
skill required to safely insert the tube, this method of deworming should be
performed only by a veterinarian.
DEWORMING SCHEDULES
The best
way to set up a deworming schedule is to consult Your veterinarian. Horses at
different ages and stages have varying needs concerning parasite control. For
example, young foals are especially susceptible to ascarid roundworm) infestation,
and may require deworming at thirty day intervals until they build some natural
resistance. Older horses turned out on a large acreage might do well on a semiannual
schedule.
And some
owners may prefer to have their horses on a continuous control program whereby
the horse is given a daily dose of dewormer through a feed additive.
Climatic
conditions and season of year can also influence parasite levels. Your veterinarian
may recommend that you concentrate deworming efforts when your horse's exposure
to Parasites is at its peak. Other veterinarians may prefer that you deworm at
regular intervals, such as every sixty to ninety days. Still others may recommend
that you prevent parasitism with a daily dewormer. In any case, the goal is to
keep parasite loads to a minimum.
A COMPLETE MANAGEMENT PROGRAM
Importantly,
chemical control is just one Part of a total parasite control plan. Since parasites
are primarily transferred through manure, good management is also key. You should:
- Pick up
and dispose of manure droppings on a regular basis (at least twice weekly)
- Mow and
harrow Pastures regularly to break up manure piles and expose parasite eggs and
larvae to the elements
- Rotate
Pastures by allowing other livestock, such as sheep or cattle, to graze them,
thereby interrupting the life cycles of equine parasites
- Group
horses by age to reduce exposure to certain parasites and maximize the deworming
program geared to that group
- Keep the
number of horses per acre to a minimum to Prevent overgrazing and reduce the
fecal contamination per acre
- Use a
feeder for hay and grain rather than feeding on the ground
- Remove
bot eggs quickly and regularly from the horse's haircoat to Prevent ingestion
- Rotate
deworming agents, not just brand names, to Prevent chemical resistance
- Consult
your veterinarian to set up an effective and regular deworming schedule
SUMMARY
With the many safe, convenient
products available today, establishing an effective deworming program is easy.
Discuss a plan with Your veterinarian and implement it without delay. A good
parasite control program will go a long way toward maximizing your horse's appearance,
performance and comfort. The net result will be an animal that's as healthy on
the inside as it appears on the outside.
This brochure was developed by the American Association
of Equine Practitioners through a grant from Bayer Corporation.
Bayer Corporation Agriculture Division, Animal
Health, Shawnee Mission, Kansas 66201
1996, Bayer Corporation
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