Those who own sheep and goats find out fairly quickly that raising these species becomes a battle against internal parasites. The less-than-judicious use of chemical dewormers over the past 40 years combined with the lack of small ruminants’ ability to develop good immunity to internal parasites has led to anthelmintic resistance, and has spurred both farmers and researchers to seek out and test alternative methods of parasite control.
“Anthelmintic resistance is the ability of worms in a population to survive drug treatment of the animal at the standard prescribed dosage,” said Dr. Dahlia O’Brien, small ruminant extension specialist at Virginia State University. “Animals that show clinical symptoms and are dewormed but don’t respond to treatment is one of the easiest ways to tell you might have some kind of resistance problem.”
O’Brien suggests small ruminant producers interested in alternative methods of deworming consider using proven natural alternatives along with chemical products to help slow down resistance.
“What I have observed is that producers who use natural or herbal dewormers have successfully incorporated them with other management practices,” said O’Brien. “They take into consideration the parasite life cycles and grazing preference of sheep versus goats.” O’Brien added that it’s difficult to determine whether or not herbal or natural dewormers are actually effective by themselves, or if efficacy is a combined effect of management practices.
Producers should always incorporate pasture management in parasite control. It’s also important to understand the life cycle of parasites, and the fact that adult worms pass eggs through the feces when warm, moist conditions are optimum for larvae survival.
“We know that very few worm larvae get higher than 2 inches from the ground,” said O’Brien. “Some get to about 4 to 8 inches, but most stay below. Trying to prevent animals from grazing below this point will help to reduce the number of worm larvae that are ingested by the animals on pasture.”
Also important when thinking about grazing management is that larvae migrate approximately 12 inches from the manure pile, so providing areas where animals can browse and eat away from manure will reduce the number of worm larvae ingested. Lower stocking rates also reduce the number of parasite larvae ingested.
Pasture rotation with other species and grouping animals by age in pasture rotations also helps reduce parasite exposure. Species such as cattle or horses can ‘vacuum’ the larvae of small ruminant parasites without ill effect. “Always lead with more susceptible species or classes,” said O’Brien. “Lead with sheep or goats before cattle, and lead with lambs before you put ewes on pasture.”
Genetic selection is another measure for parasite management. Several breeds of sheep and goats are more resistant to parasites, including Barbados Blackbelly and Texel sheep, and Spanish, Kiko and Myatonic goats. However, animals must still be managed appropriately and not expected to simply resist parasites because of their breed. “There are individuals within any breed that will be more resistant to parasites,” said O’Brien. “These are the ones we should be selecting for our flock or herd.”
Producers who are using FAMACHA as part of a strategic deworming program should cull any susceptible animals. “These are the animals that always have a high FAMACHA score and are the ones that have to be constantly dewormed,” said O’Brien. “By culling these susceptible animals, you’re increasing flock resistance, reducing pasture contamination and decreasing deworming frequency. The reduction in pasture contamination is especially important for young animals you’re putting on those pastures.” Because there’s a genetic component to resistance, offspring of animals that require frequent deworming should not be retained in the flock.
O’Brien emphasizes the fact that good nutrition supports the immune system and results in higher tolerance of internal parasites. “Ewes receiving higher levels of protein 6 weeks prior to lambing have significantly lower fecal egg counts compared to those that were not supplemented,” she said. “Legumes provide more protein and can help protect animals from internal parasites. Sheep and goats in confinement or dry lot have fewer parasite issues because they aren’t constantly picking up larvae from pasture.”
Some producers have chosen to use natural dewormers in addition to or in place of chemical products. O’Brien has conducted research on the efficacy of herbal dewormers including garlic, papaya, pumpkin and ginger. However, she says much of the evidence of efficacy is anecdotal and somewhat inconsistent.
O’Brien describes a producer study involving garlic in which one teaspoon of garlic juice diluted in water was administered to lambs in organic production. Fecal samples were collected for fecal egg counts (FEC) every 2 to 3 weeks from May through September. The four treatment groups including one control, two groups that received a commercial herbal dewormer and one group that received garlic. “We know that garlic has antimicrobial properties and helps boost the immune system,” said O’Brien, adding that the active ingredient in garlic is allicin. “The producer reported that animals that received garlic had lower fecal egg counts compared to other treatment groups.
An Arkansas study of kids and lambs treated with garlic juice resulted in no reduction in fecal egg count. “An additional experiment looking at papaya seeds reducing fecal egg count also demonstrated that it had no effect on fecal egg count,” said O’Brien, adding there is no way to positively differentiate parasite eggs in a fecal egg count other than hatching them out.
In another study, meat goat kids were given papaya juice, but fecal counts were not lowered in this treatment. When O’Brien tested pumpkin seeds and ginger as a deworming treatment, the goats sorted through the seeds and avoided eating them, so she had to create a pumpkin seed drench to ensure each animal a received sufficient dose. “Goats received a pumpkin seed drench, a ginger drench or no treatment every other day over a 42-day period,” she said. “There was no statistical effect of treatment on fecal egg counts, but I noticed that we had to remove and deworm more animals from the control and ginger group than from the pumpkin seed drench group.” At slaughter, animals that had received the ginger and pumpkin seed treatments had fewer abomasal worms than animals in the control group, a possible indication that the treatment had some positive effects.
O’Brien says some producers use commercial herbal dewormers that contain ingredients such as wormwood, fennel and black walnut. In a study of goat kids, the commercial product did not reduce FEC when used according to instructions. In a study of lactating does that were given an herbal dewormer, results showed a lower rate of increase of FEC in the treatment group compared to the control group. “There is a lot of anecdotal evidence that herbal dewormers work,” said O’Brien, “but there is lack of scientific support, and when there is support available, there are inconsistent results.” O’Brien says the reason for this is that active ingredients vary, and common names of plants don’t always refer to the same plant. Additionally, the ingredients may not be present in high enough or consistent levels to produce anthelmintic properties.
Some producers report success with diatomaceous earth (DE), but there is no conclusive evidence to show DE is an effective treatment for parasitism. “While DE has some insecticidal properties,” said O’Brien, “the majority of controlled studies in sheep, goats and cattle show no significant impact on internal parasite infection.” O’Brien added DE contains trace minerals that might provide a boost in immunity, but there’s no scientific data to prove that.
For those who want to use natural dewormers, O’Brien suggests using them in combination with other parasite management techniques. “It’s important to know the level of drug resistance on your farm so that these techniques can be used in conjunction with an effective chemical dewormer.”