Farming Magazine - December, 2013


Small Livestock: Do Natural Dewormers Work in Sheep and Goats?

By Sally Colby

Grazing chicory may be effective as part of a comprehensive parasite control program for sheep and goats.
Photo by Susan Boyer, courtesy of USDA-ARS.

Anyone who raises sheep or goats is familiar with the serious problem of resistance to currently available anthelmintic (deworming) products. The problem isn't new, but the issue of increased resistance has forced farmers to search for alternatives. Although studies have shown that alternative dewormers might play a role in a comprehensive parasite control program, a combination of traditional methods and alternatives will likely provide the best results.

Dr. Enrique Nelson Escobar, small ruminant specialist for the University of Maryland, has been studying the issue of resistance and the use of alternative products. Although he has seen some favorable results from research into alternative dewormers, Escobar is quick to point out that one popular alternative, diatomaceous earth (DE), is not an effective dewormer.

Why is it worth pursuing the search for alternative or natural dewormers? Escobar says that it's a combination of a need for organic production and the need to delay resistance of parasites to available anthelmintic products. However, despite extensive research and study, Escobar says there are no unconventional products that are reliably effective.

"When we talk about natural dewormers, it's a matter of identification and labeling the compounds," said Escobar. "For example, about five years ago there were reports that pumpkin seeds reduce worms in small ruminants. We measured that with fecal egg counts. So we tested pumpkin seeds extensively, but we cannot find any positive effect."

Escobar says that the term "natural compounds" is very broad, which makes it difficult to determine what is natural. Referencing the pumpkin seed example, Escobar says that Cucurbita pepo, the Latin name for pumpkin, comprises thousands of varieties. "We don't know exactly which variety the pumpkins were," said Escobar. "We need to be very specific about which species and variety."

The potentially effective compound in pumpkin seeds is cucurbitacin, but Escobar says that it's difficult to measure that compound precisely. "I spent almost nine months trying to find a lab that could do it, and it took quite a while to conduct the study," he said. "We need to find out which compound in the natural anthelmintic is the one that's affecting the worm, instead of studying the compounds first and then trying to mimic that."

One issue with natural dewormers is that they are often unpalatable, and animals tend to sort feed and avoid ingredients that are unpalatable. In the pumpkin seed study, goats were sorting the seeds and not consuming them. The solution was to grind the seeds at the farm and take the ground material to the feed company so the ground seeds could be incorporated in the pellets - an extra expense that probably wouldn't return significant benefits.

Garlic is another popular natural dewormer. It has been effective in some cases and ineffective in others. Escobar says that some producers have used garlic extract, while others have fed the whole clove, with no firm results either way.

The most promising research shows that pasture plants high in condensed tannins may have an anthelmintic effect. Chicory and sericea lespedeza are two such plants. Both have condensed tannins, and although it isn't clear how those compounds affect parasites, plants containing tannins may play a role in a comprehensive parasite control program. Several studies conducted in Alabama and Georgia showed a significant decrease in fecal egg count (FEC) in just a few days when animals grazed pastures containing high-tannin plants. When the animals were removed from those pastures, FEC went up. Although FEC shouldn't be the only part of a parasite monitoring program, Escobar says it is a valuable tool and provides a good "snapshot" of eggs being shed.

At the University of Maryland Eastern Shore, Escobar and his colleagues are developing a study in which animals will rotate fescue, bermudagrass and lespedeza pastures. In this rotational grazing system, the animals will graze the fescue, then move to the bermudagrass, followed by lespedeza. "They'll go around that rotation and have lespedeza in their systems all the time," said Escobar, who is still designing the study. "My thought is if they are in the lespedeza at least three days a week, the animals will have a reduced FEC."

Escobar stresses the fact that the worm population on individual farms is unique; not every farm in a particular area will have the same parasite level, and not all animals will have the same parasite burden. Because of this, it's imperative for each producer to be aware of parasite levels on that farm. Secondly, producers need to know which dewormers the parasites in that population are resistant to. The only way to determine that is through an FEC reduction test. "The reason it's important to know what the worms are resistant to is because you need to have on hand one anthelmintic that works," said Escobar. "Then treat the animals that need to be treated, identified through FAMACHA. That's what should be done to reduce the chance of more resistance in the flock or herd."

Producers should understand that FAMACHA, which is based on a measure of packed cell volume, applies only to Haemonchus contortus and not other parasites. However, when larvae are hatched and examined by a parasitologist, 80 to 100 percent of eggs in a fecal egg count are H. contortus. FAMACHA won't solve the resistance problem, but when used properly it's a valuable tool that helps producers determine which animals should be treated for H. contortus.

Unfortunately, no single effort is fully effective against parasites. Escobar urges producers to develop an integrated parasite management program and reminds them that with the introduction of new animals to an existing group, there are different parasite levels and challenges. "If a farmer is going to buy new animals, one question they should ask is: When is the last time the animal was dewormed?"

The author is a frequent contributor and freelance writer who farms and raises Great Pyrenees in south-central Pennsylvania. Comment or question? Visit and join in the discussions.