Sheep Industry News March 2023

Integrative Parasite Management Includes Genetics

CAT URBIGKIT The Shepherd P arasite management and Western range breeds was the subject of a presentation by Jake Thorne, sheep and goat program specialist at Texas A&M AgriLife (and currently working on his doctorate through the University of Idaho) at the Genetics Forum during the ASI Annual Convention in Fort Worth. While many associate barber’s pole worm with hot, humid areas of the country, this nematode has been working its way through the arid West. Thorne explained that the worm needs warm weather – 50 to 90° F – forage and moisture such as rain or dew. In the West, it’s found in irrigated fields, smaller pastures and areas subject to constant grazing such as near water sources in larger pastures. The parasite causes anemia, bottle jaw and death in sheep. What sets the barber’s pole worm apart from other gastrointes tinal parasites is its extremely high rate of prolificacy, Thorne said, noting a single worm’s ability to produce 10,000 eggs per day. “That’s much higher than any of the other worms,” he said, which is a key factor in its resistance to anti-parasitics as well. “It’s a formidable opponent for the sheep industry,” Thorne said. It’s the most economically significant parasite of sheep and goats throughout most of the country. It’s important to understand the life cycle of sheep worms, Thorne said. Adult worms lay eggs which pass onto pasture in dung. If the weather is suitable, the larvae hatch. Within 6 to 10 days, the larvae migrate in films of moisture from dung pellets onto pasture. The infective larvae are then eaten by sheep, and the larvae in the gut develop into adults in about three weeks, at which point the cycle can begin again, perpetuating parasite infections. While many things impact susceptibility to parasite infection, Thorne said there are resistance and susceptibility differences be tween sheep breeds. Breeds that were developed in more parasite rich environments such as the Caribbean are known for having a natural parasite resistance. In contrast, Western white-faced range sheep breeds are much more susceptible. Thorne explained that parasite resistance is the ability of the sheep to mount an immune response to neutralize the parasite before it develops into a full-blown infection. Thorne said producers should think about the sheep that they

put into situations such as smaller pens or irrigated pastures with good forage – often they are animals that need some special care such as ewes that have just lambed, or just-weaned lambs. “Those are often the classes of sheep that are most susceptible,” he noted. Treatment for these parasites is based on three classes of de wormers: • Nicotinic agonists such as Levamisole or Prohibit; • Macrocyclic Lactones such as Cydectin and Ivermectin; and • Benzimidazoles such as Valbazen and Safe-Guard. Since barber’s pole worm is resistant to all classes of dewormers in the United States, it’s important that the treatment program is vigorous. Thorne said producers should use a full dose of dewormer from at least two of the dewormer classes listed above, while being sure to use products from two different classes of dewormers rather than simply two types of dewormers from the same class. He also recommended that drench be used rather than injectables. Thorne emphasized that producers need to read the product labels and fol low the instructions in using drugs on their animals. A final option is the use of copper oxide wire particle bolus, which has been shown to reduce barber’s pole worm infections and may increase the efficacy of commercial dewormers. Find more information about COWP at wormx.info, the website of the American Consortium for Small Ruminant Parasite Control. Thorne said that an integrative management program for parasite control should include combination dewormers using a selective treatment, pasture management practices such as rations, forage heights and types, and genetic selection that includes cull ing susceptible stock and purchasing stock using estimated breed ing values for parasite resistance. Thorne advised that the best tool to increase parasite resistance is to use NSIP’s EBVs in selection. Thorne advised that producers cull out sheep that are carrying high parasite loads, as research indicates that 20 percent of the sheep are carrying 80 percent of the worms. NSIP In other Genetics Forum business, Rusty Burgett presented an update on achievements for the National Sheep Improvement Program in 2022, noting there are now more than 524,000 sheep and goats with estimated breeding values in the NSIP genetics database.

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