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Parasite control: ASI hosts management strategy webinar

by Wyoming Livestock Roundup

ASI hosts management strategy webinar

The American Sheep Industry (ASI) sponsored a webinar on May 26 titled “Integrated Parasite Management Strategies for Sheep Producers” featuring North Carolina State University Extension Small Ruminant Specialist Dr. Andrew Weaver discussing parasite management strategies, parasite biology and host-parasite interactions. 

Parasite biology 

Weaver shares when developing a management strategy, the first thing to understand is the biology of a parasite.

“There are a lot of worms that could infect our animals,” he states. “A lot of them fall in a family of parasites called strongylid nematodes.”

He notes protozoa parasites are also of concern, in addition to helminths and ectoparasites. A common parasite impacting sheep and goats is Heamonchus contortus, otherwise known as a stomach worm. 

By understanding the lifecycle of a parasite, producers can then implement different management strategies to help mitigate infection. 

Eggs are first deposited into the feces of the sheep, hatch within one to two days into L1 larvae and, as they grow, they develop into L2 and L3 larvae.

“The L3 stage is very important,” he shares. “It’s the only infectious stage to the host. The sheep can consume as many L1 and L2 larvae as they want and they will never get infected. It’s only the L3 larvae that can infect the host.” 

Once L3 larvae is consumed by the host, it molts into L4 larvae, then the adult worm. 

Managing parasites: Determining which
animals to deworm

Producers first need to identify the problem when livestock become sick – whether it’s from a parasite or something else. 

“There is no point in spending our resources when it’s not a problem,” mentions Weaver. “We first need to identify the problem and what parasite is causing this problem, and we can then accurately determine how we’re going to address it.” 

A common quote Weaver recalls is, “You can’t select or improve something you don’t measure.” 

He encourages producers to measure traits associated with parasitism in order to make data-driven decisions to manage the infection. 

“A simple place to start is deworming records,” he says. “Many producers already do this, it’s something easy to record and is a great place to start if records are not currently being kept.” 

He encourages producers to keep track of dewormed animals, dates and dewormers used. He notes a con of deworming is producers don’t know the actual parasite infecting the host. 

One tool, FAMACHA scoring, uses a numeric score to identify and selectively deworm sheep and goats with anemia. Scoring requires producers to assess anemia status based on mucus membrane color around the eye.  

A more parasitized animal will have paler coloration. It’s an easy, on-farm assessment, but it is only relevant to Haemonchus contortus infections and is somewhat subjective. Training is required, he shares. 

Other assessment tools include a five-point check, which is a comprehensive analysis of an animal’s condition and need for deworming. 

Deworming effectiveness

“Fecal Egg Counts (FEC) are simply the measure of the number of strongylid parasite eggs in one gram of fecal matter,” he says. “It’s very important to understand we can’t distinguish the different types of strongylid parasites by the egg stage.” 

This process requires a larval culture to determine what species of a parasite is infecting the host. FEC is taken at the time of deworming, then taken again 10 to 14 days later, and there should be a 95 percent or greater reduction in FEC. If there is not at least a 95 percent reduction, this tells producers the dewormer was not as effective as it should be, he explains. 

“This can be a great tool to determine if our deworming products are effective and serves as a valuable selection tool for improving parasite resistance in a flock,” he says.  

Corrective actions 

“Unfortunately, there is no single tool or method as a golden ticket,” he says. “Rather, a combination of multiple tools and methods is the best solution to manage parasitism.”

From an environmental perspective, a producer can manage parasites through forage height and/or grazing rotation, stocking rate, tannin-containing forages, multi-species grazing and supplementation rate. From an animal management system, producers can consider  targeted selective treatment, combination treatments, copper oxide wire particles and genetic selection. 

He encourages producers to select several of these tools to effectively manage parasite populations. 

“There are a lot of tools available to put in a toolbox, and producers need to create a plan – think what is practical and what can be implemented and use a combination of different methods,” he notes. “Think about multiple tools and how they will work together.” 

He encourages producers to continue monitoring parasites to ensure management tools are working. 

“After producers implement these tools, they need to continue to monitor and evaluate results to make sure the plans they put in place remain effective,” he says. “If producers continue to have high FEC, explore other options and add tools to the toolbox.”

Brittany Gunn is the editor of the Wyoming Livestock Roundup. Send comments on this article to 

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