Sheep producers running out of options when it comes to controlling parasites |

Sheep producers running out of options when it comes to controlling parasites

Whit Stewart, University of Wyoming sheep Extension specialist, discusses parasite control during a recent Nebraska Sheep and Goat Producers meeting.
Photo by Teresa Clark

During a recent Nebraska Sheep and Goat Producers meeting, a sheep producer questioned if his dewormer was working. Some of his ewes were thinner, and after using a deworming product, some of the ewes would recover and some wouldn’t. He questioned what his next step should be.

University of Wyoming Sheep Extension Specialist Whit Stewart shared with producers some avenues they could look into, since parasites are becoming more and more resistant to many of the products left on the market. “Looking at the spectrum of products available, we basically only have four active ingredient products to work with on label. If you work with a veterinarian, you may be able to get some extra label products. We are generally limited to this toolbox. The problem is the eastern part of the U.S. has used up everything in their toolbox, and no longer have any options. What we are trying to do here is slow down the resistance, so we can utilize these products when we need to and solve the problem,” he said.

Ranchers with large range sheep flocks find there isn’t enough moisture in the state of Wyoming to generate many parasite problems. In fact, Stewart said one range producer was deworming his sheep twice a year. After a fecal egg count was taken, he discovered his sheep never had parasite problems, so he didn’t need to deworm at all. He was able to save more than $6,000 a year.

Other producers aren’t so lucky. Smaller farm flocks that graze on sub-irrigated and irrigated land, meadows, riparian areas and even dry lots are much more susceptible to parasites, Stewart said. “Continuous grazing with rainfall creates the perfect environment for parasite infestation. Parasites need warm temperatures, humidity and water. A lot of the smaller flocks are maintained on irrigated pasture that simulates the environment needed for parasites to thrive. Flood irrigation will bust up that fecal pellet so the larvae can escape and climb up the plant to be consumed,” he said.

A rancher near Kalispell, Mont., was running 300 ewes on sub-irrigated meadow in a hot, humid environment. The producer was deworming the sheep every 10 days, but the dewormer wasn’t working. Stewart said fecal samples were taken and sent in to a lab to analyze for resistance to all classes of dewormers. The test is expensive, but Stewart said it told the producer which dewormers could still work on that particular flock.

He said three ranches where the sheep grazed on sub-irrigated or sprinkler irrigated grass submitted fecal samples to a laboratory. The average fecal egg count was 3,800 eggs per gram. Stewart said if the fecal egg count is above 500 eggs per gram, it’s a good indication the animals need treatment.


Stewart encouraged sheep producers to collect samples from their flock if they suspect parasite problems. A fecal egg test costs between $25 and $40. The producer will need to collect samples from 5-10 percent of the flock, and put the samples into one big sample and send it to a laboratory. The laboratory can determine what parasites are present, how many eggs per gram, and give the producer an idea if the flock needs treatment.

Stewart asked producers where they purchased their last stud ram, and if they knew what that producer’s deworming program was. The ranchers answered with Nebraska, North Dakota, Minnesota, Kansas and Oklahoma. “I noticed no one mentioned buying rams from Wyoming, New Mexico or Colorado, which are drier, arid areas,” he said. “The point I am trying to make is we are buying parasite issues by the animals we bring into our flock. When you brought in new genetics, you also brought in new parasites.”

Haemonchus contortus, also known as the barber’s pole worm, is the most aggressive internal parasite producers have to deal with, Stewart said. “The barber pole worm represents 90 percent of the problem in the U.S. and internationally,” Stewart said. “It infects the abomasum of the digestive system, which is the last compartment of the rumen and one of the most important parts of the stomach. It busts up all those microbes, and gets them ready to be absorbed down the system. The problem with parasites is they cause anemia and weight loss because these organisms can shut down the ability of the animal to digest food.”

Stewart told producers to use body condition as a tool to use to detect parasite presence. Other clinical signs are weight loss, loose stool and a chalky appearance to the fleece. “It’s not uncommon to have 5,000 worms present in a clinical case. They can consume a cup of blood every day,” he said.

The worms only method of transportation is through grass or water. “Understand that they don’t inch up like a typical worm,” he said “They get ingested according to the dew line — mostly when pastures are grazed down low. It takes seven days from the time they are hatched in a fecal pellet to become a stage three larvae. Once they are ingested, it takes another three weeks for them to develop in the animal. If you understand that time line, you will realize there is some lag time. Even if you have sheep in a dry lot and you have some precocious lambs, they will pick up those eggs and ingest them.”

“Another misconception is they overwinter in the pasture, but research suggests they don’t overwinter in the fecal pellet, but inside the animal. If you are using a product that isn’t working, it will kill some of the worms, but the rest will hold over and stay in the system for a long time continually shedding eggs into your environment,” he said.

Stewart said in addition to fecal egg counts and body condition scoring sheep, producers should learn how to FAMACHA score sheep to determine which ones are anemic and may need treatment. A local extension specialist should be able to put producers in contact with someone who trains in FAMACHA scoring, he said.

Pasture rotation and resting pastures for at least 30-45 days can also kill worm populations. “Worms stay in the bottom 3 inches of the plant because the sun will decimate the worm, dry it out and kill it,” he said.

Stewart also recommends rotating classes of deworming products or even doubling up on wormers at full dosage if the infestation is severe.

A diet unappealing to parasites can also be fed to sheep, which Stewart believes may be the next best option after natural control methods. Studies have indicated Birdsfoot Trefoil or Sandpoint have condensed tannins which may inhibit the L3 larvae and help sheep respond to parasite threats. If producers choose to use either forage, it needs to be fed as the majority of their diet. Stewart said they can be harvested as first or second cutting and fed to the sheep after deworming treatment to help with parasite control.

Distillers meal or soybean meal can also be fed to animals to help them recover from parasite infestations. “Any protein source high in bypass protein or undegradable protein is going to help the ewe recover faster than feed where she has to use her abomasum. These types of feeds will bypass the abomasum and go directly into the small intestine to be absorbed,” he said. ❖

— Clark is a freelance livestock journalist from western Nebraska. She can be reached by email at