Assessing treatment options and using FAMACHA
Internal parasites are the bane of anyone who raises sheep or goats. However, there are strategies to help producers manage parasites such as Haemonchus contortus (barberpole worm), which is responsible for major losses in the industry.
Dr. Andrew Weaver, assistant professor and Extension small ruminant specialist at North Carolina State University, explained the importance of knowing which animals require treatment and how to determine whether treatment is effective.
Most small ruminant producers are familiar with FAMACHA scoring, which assesses the anemia status of animals based on the mucous membrane color around the eye. Paler color indicates anemia. Assessing anemia using FAMACHA is an easy on-farm assessment, but Weaver reminded producers that Haemonchus is the only worm that causes anemia so FAMACHA is only effective for estimating Haemonchus burden. Proper training helps limit the subjective aspect of the using FAMACHA.
Along with FAMACHA, Weaver suggested using a five-point check system, a holistic approach that considers other indicators that parasites might be a problem. “We look at the eye, the body condition score, rear end for dag score (soiling) and evidence of bottle jaw that results from hyperproteinemia,” he said. Nasal discharge (due to bots) is not as common but worth noting during a check.
The use of fecal egg counts (FEC) is another important tool. “It’s a measure of the number of strongylid parasite eggs in one gram of fecal matter,” Weaver said. “It’s important to know we cannot distinguish the different types of strongylid parasites by the egg stage – we can’t look at the egg and determine which parasite it came from.” It’s fairly safe to assume that in most sheep operations the majority of strongylid eggs will be Haemonchus, but a larval culture is the only way to determine exactly which species are present.
Determining whether deworming products are effective can be done through FEC reduction. This involves measuring the FEC at the time of deworming, then measuring another sample about 10 to 14 days later. “We should see a greater than 95% reduction (in eggs per gram of feces),” said Weaver. “If we see less than 95% reduction, the dewormers are not as effective as they should be.” While measuring adult worm burden would be helpful in assessing parasite levels, Weaver said that’s impossible other than via necropsy and counting worms in the abomasum. However, an accurate FEC is directly related to adult worms in the gut.
The old standard of treating all sheep with a dewormer, whether they need it or not, is no longer a viable parasite management option. A given population of worms includes males and females, some of which are resistant to dewormers. “When we treat with a dewormer, we wipe out the susceptible population,” he said. “What’s left is the resistant population. Think of using a dewormer as applying selection pressure toward the resistant worm population. When we treat with a dewormer, we’re selecting for and generating more resistant parasites. The more we do that, the greater population of resistant worms we’ll have, and the less effective dewormers will be.”
One challenge in selecting deworming products is that there are only three chemical classes of dewormers, and resistance has developed to all three classes. That means those who raise sheep or goats can no longer rely solely on chemical treatments to manage internal parasites. “We need to do anything we can to maintain the effectiveness of deworming products,” said Weaver. “We haven’t had a new class of dewormers in 30 to 40 years.”
One critical aspect of managing parasites is knowing which animals are most susceptible. While lambs begin life with a low FEC, parasites start to become problematic when lambs are about one month old. This is due to the parasite development lag time of about three weeks from the time lambs begin to graze.
“Fecal egg counts in lambs peak at around 120 to 130 days, and either their immune system recognizes the parasite infection and the parasite burden decreases on its own, or we treat the animal,” said Weaver. “Or the animal doesn’t respond to the infection and FEC continues to rise until the animal dies. The month or two following weaning is a period of high susceptibility and FECs are generally going to be high.” Animals are likely to be infected during that time, so having strategies in place will help mitigate the infection level. Twins and triplets are generally more susceptible to parasites, so pay close attention to them.
Since no single parasite management method will work for every farm, farmers must use a combination of tools to develop an integrated parasite management plan. Considerations for environmental management through grazing include forage height/rotation, stocking rate, forages with tannins and multiple species grazing.
Understanding the parasite lifecycle and temporary fencing can help minimize exposure to the infective L3 larval stage. “Rotate animals at least every three to five days – in hot, humid weather, maybe more frequently,” Weaver said. “It takes a week to two weeks from the time eggs are shed until there are infective larvae. If we move animals every three to five days, we’re moving animals faster than infective larvae can develop, so by the time infective larvae are present on pasture, animals have moved to the next paddock and grazing fresh forage.”
About 90% of infective L3 larvae reside in the first four inches of forage, so avoiding overgrazing can help minimize exposure to infective larvae. “If in doubt, move them,” said Weaver. “More frequent moving is good for parasite mitigation and avoiding exposure to infective larvae, and also good from a forage health standpoint.”
Adjust stocking density helps but varies according to farm and location. Consider forage height, growth and weather along with adequate rest periods for paddocks of at least 45 days. However, with longer rest periods, forage quality decreases, so managing forage for both quality and parasites involves planning and flexibility. Some producers graze a paddock early in the season, then allow forage to grow to an appropriate height for hay. As hay dries, parasites die.
Selecting high-tannin forages such as bird’s-foot trefoil and sericea lespedeza (Chinese bushclover) to a grazing mix can help reduce parasite burdens. “Tannins improve protein availability for the animal by binding protein at high pH and releasing protein at low pH,” said Weaver. “They bind up protein in the rumen, carry protein to the abomasum where it is released and digested. Anything that improves rumen bypass protein helps animals combat parasite infection.”
Some producers choose to supplement animals with a concentrate such as corn/soybean-based feed. FECs can drop significantly when animals receive a concentrate feed at 2% of body weight. Supplementation reduces potential parasite burden and increases performance, as it helps the animal directly respond to a parasite infection.
While some producers use mixed species grazing, Weaver said data on that practice are limited. It’s important to note that sheep, goats, alpacas, llamas and deer share parasites with one another but not with cattle. “They consume larvae that would infect the other species; larvae die as they pass through the digestive tract,” he said. “Sheep are cleaning up cattle parasites and cattle are cleaning up sheep parasites.”
by Sally Colby