Preventing Deer Worm Infection in Goats

Meningeal deer worm infection requires the presence of both white-tail deer and gatropods (slugs or snails). So it stands to reason that at the top of the list of suggestions for preventing deer worm infection in goats and sheep is to control both white-tail deer and gastropods.

That’s right up there with expecting us to herd cats!

Controlling White-Tail Deer

If you feed your local deer, a good starting place is to avoid placing feeders near where goats graze. A guardian dog may also discourage deer from hanging around.

An often repeated suggestion is to avoid grazing goats in pastures adjoining woodland where deer abound. Our entire farm, like many in our area, is surrounded by deer-infested forest. So we don’t have much choice about grazing locations. Where deer favor certain grazing areas over others, an option is to make hay from the fields the deer prefer.

Even if deer don’t graze in the same pasture as goats, they will pass nearby and leave their calling cards. Gastropods don’t respect fences and can easily crawl from a deer grazing area to a goat grazing area.

Controlling Slugs and Snails

Snail bait isn’t a reasonable way to control gastropods in pasture. For one thing, massive amounts would be needed to cover all areas. Besides, some snail baits are toxic to dogs and cats. Not to mention the fact that they pollute waterways.

Far safer, and easier, is to maintain a flock of poultry — chickens or guinea fowl — along with the goats. We have large flocks of both, which may account for why we didn’t have a deer worm issue for three decades. Then our spring and fall weather got wetter and the slugs got more numerous.

Ducks are better at controlling slugs and snails. But they also like to play in water, which only attracts more gastropods.

Because slugs and snails prefer moist areas, keep goats or sheep from grazing in poorly drained pasture. Or improve drainage so puddles don’t accumulate. Also keep pastures clear of gastropods’ favorite hiding places — stacks of lumber, piles of rocks, and mounds of discarded waste hay.

Slugs and snails may be further discouraged by plowing around the outside of the pasture fence. And also by regularly mowing pasture grass to open the land to sunlight’s warm rays.

Weather Considerations

Sunlight and drying will kill larvae clinging to deer pellets. At the same time, it will cleanse the pasture of the nasty stomach and intestinal worms that plague goats and sheep. In addition to destroying worm larvae, hot dry weather decreases slug and snail activity.

Unfortunately, winter freezing doesn’t much affect deer worm larvae. But cold weather does hinder gastropod activity, and at freezing temperatures they hibernate.

So in areas that experience winter freezes and warm summer dry spells, slugs and snails are most active during spring and fall. They like damp weather with mild temperatures.

In Tennessee, our periods of greatest gastropod activity are the rainy seasons of early fall and late winter. In Texas the peak season is spring. In states farther north, the peak period is late summer to early fall.

One recommended option for such areas is to remove goats and sheep from pasture when gastropod activity is greatest. In other words, basically keeping the herd in a barn or on a dry lot. Here in Tennessee, as in many other places, that would mean keeping the animals off pasture when grazing is optimum.

Controlling Deer Worms

Owners of alpacas and llamas (camelids) control meningeal worm with regular deworming. Where the weather is mild year round, deworming must be done every 4 to 6 weeks.

Deer worm don’t reproduce in animals other than white-tails, so they cannot become resistant to dewormers. However, camelids now suffer from large burdens of other parasites that have become resistant to dewormers. The treatment intended to prevent one problem has created an even bigger problem.

Temperate-climate goat and sheep owners are therefore between a rock and a hard place with respect to using dewormers to control deer worm. But those of us who live in areas that enjoy seasonal temperature extremes have an option other than year-around deworming. Since the risk of exposure to deer worm is lowest during prolonged periods of dry heat or deep freezes, we can opt to skip deworming during those periods of low or no slug and snail activity.

Such a plan does not offer 100% protection against deer worm. But it does help prevent the much worse problem of creating drug resistance in other killer parasites.

As a dewormer, the macrocyclic lactone ivermectin (Ivomec or Noromectin) is the most effective against deer worm larvae that have not yet crossed the blood-brain barrier (see below). The late Cliff Monahan, DVM, PhD, of the Ohio State University’s College of Veterinary Medicine, suggested that instead of ivermectin, using a longer-acting macrocyclic lactone would reduce the overall number of treatments. The result is to delay or avoid the development of drug resistance. These long-acting dewormers require a prescription, so discuss this option with your veterinarian.

Feasible Options

Since goats and sheep are largely resistant to deer worm, another potential course of action is to cull susceptible individuals from your herd. That would be a difficult choice for those of us with small herds, in which every individual has a name and seems like family. So we are left with these options for reducing the risk of deer worm infection in our goats and sheep:

• Do not actively encourage deer to hang around.

• Keep the pasture environment unfriendly to slugs and snails.

• Deworm following peak seasons for slug and snail activity.

• Know the signs of deer worm infection and begin treatment at the first signs.

Above all, remember these important points: Deer worms do not spread from one goat or sheep to another. Therefore, the survivor of a deer worm infection cannot infect other animals in your herd.

Blood-Brain Barrier

Fenbendazole (SafeGuard or Panacur) is the dewormer of choice for deer worm treatment, but a macrocyclic lactone such as ivermectin (Ivomec or Noromectin) is preferred as a preventive to kill worm larvae before they enter the spinal cord. Although ivermectin destroys deer worm larvae better than fenbendazole, it does not penetrate the blood-brain barrier as readily.

The blood-brain barrier is an important factor in the course of deer worm infection and in treatment. It consists of a layer of cells separating blood circulating in the body from brain fluid in the central nervous system. The blood-brain barrier performs these important functions:

1. It protects the brain from bacteria and other harmful substances in the blood.

2. It protects the brain from the body’s normal hormones and neurotransmitters.

3. It provides a steady environment that allows the brain to function effectively.

The blood-brain barrier is selectively permeable. As such, it prevents some substances (such as certain drugs, including ivermectin) from entering brain tissue, while allowing other substances (including fenbendazole) to enter freely.

Inflammation makes the blood-brain barrier more permeable than usual. Deer worm infection may therefore break down the barrier, allowing penetration by ivermectin. But ivermectin is a potential toxin to the mammalian nervous system. So fenbendazole is used for treatment, ivermectin for prevention.