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External parasites discussed

by Wyoming Livestock Roundup

Published on March 28, 2020

Dr. Shaun Dergousoff, research scientist at the Lethbridge Research and Development Centre and Katelyn Rochon, associate professor of veterinary and wildlife entomology for the University of Manitoba, discussed how to control external parasites in beef cattle operations during the March 12 episode of the Beef Cattle Research Council’s (BCRC) podcast. 


            To begin their talk, Dergousoff notes in order to manage a parasite, one must understand what they are. Therefore, he explains a parasite is a living organism that is usually very small and lives at the expense of another organism of a different species. 

            In their discussion, Dergousoff and Rochon focus on ectoparasites, which live or feed on the outside of their host. 

            Dergousoff notes there are 13 different types of ectoparasitic species affecting beef cattle. These include chewing lice, sucking lice, ticks, biting midges, mosquitos, horn flies, stable flies, horse flies, deer flies, black flies, face flies, house flies and mange mites. 

            “All of these different species have a wide range of effects on their animal hosts,” states Dergousoff. “They can cause pain and irritation which can cause potential injury and lead to stress. Animals under heavy pest pressure might change their feeding behaviors or their grazing patterns to avoid these insects.” 

            Dergousoff explains this can cause negative effects on weight gain and milk production in cows, which also affects calves. He also notes they may act as vectors and transmit pathogens between infected and healthy animals. 

            “There is quite a long list of pathogens these 13 different species of parasites can transmit. There is anything from bovine anaplasmosis, epizoonotic haemorrhagic disease, bluetongue, pinkeye and eyeworms,” says Dergousoff. 

            “They can also carry diseases that affect humans including West Nile virus, eastern equine encephalitis, lyme disease, anaplasmosis, babesiosis and Powassan encephalitis,” he says. 

Integrated pest management

            Dergousoff notes loss of production and disease transmission are two major reasons pest control is an important consideration in beef cattle production systems. 

            “When we are looking at pest control, the goal is to reduce the harm to livestock and therefore reduce production losses,” states Dergousoff. “It doesn’t necessarily mean we are going to try to eliminate the pests, but we can at least reduce numbers so none of these things happen.” 

            To do this, Dergousoff says producers should adopt integrated pest management (IPM) practices. 

            “IPM is when we use multiple different control methods together to really reduce the number of pests below an economic threshold,” he explains. 

            Dergousoff further explains there are four steps to implementing IPM on an operation. 

            The first step he mentions is to assess the pest population. He notes it is important for producers to understand what kind of pests they are dealing with and how many of them there are. 

            The second step, according to Dergousoff, is to evaluate options for prevention and treatment. 

            “We have three different types of control options – biological, cultural and chemical,” he says. “Biological control uses living organisms, parasites or predators to kill the pests. Cultural control includes farming practices that reduce pest numbers and frequency of outbreaks. 

“This includes sanitation, water and manure management and paying special attention to fence lines, silage mounds and areas where there is spilled feed,” says Dergousoff. 

            “Chemical control is the most common method and it is important, but we really need to consider the timing of application, mode of application and the class of the insecticide used,” he adds. 

            The third step of IPM is implementing a control method the producer has deemed appropriate for their situation. 

             “The fourth step is to evaluate the effectiveness of the measures we are taking,” states Dergousoff. “We can do this by observing if the abundance of the pest rebounds or declines, if there is a resurgence of the pest and determining if and when we need to treat again.” 

Horn flies

            “Horn flies are mainly a problem in pastures and rangeland, but they are one of the most damaging pests economically for cattle producers,” Dergousoff states. 

            He explains horn flies are about five millimeters long and are a charcoal grey color. He also notes horn flies stay on animals for a long period of time and can often be found on the head, shoulders and back. 

            “In response to horn flies, producers will often see cattle start bunching up even in open spaces. They will stomp and flick their ears and tail,” Dergousoff explains. “This behavior can cause significant loss.”

            Dergousoff says horn flies can be managed through a number of different methods. These include cultural methods such as walk-in traps and breaking down manure piles, biological methods such as dung beetles or ducks and chickens, which will eat the fly larvae out of manure piles and chemical methods such as fly sprays, pour-ons, ear tags, back rubbers and oilers, dustbags and feed-through insecticides. 


            “Another important pest found in field situations are ticks,” says Dergousoff. “There are five important species, including the American dog tick, Rocky Mountain wood tick, winter moose tick, lonestar tick and Asian longhorned tick.” 

            Dergousoff explains ticks can be vectors and transmit disease as well as cause irritation and blood loss. 

            Control options for ticks, according to Dergousoff, include cultural methods such as removing ticks from animals, reducing favorable habitat through vegetation management, keeping animals away from favorable habitat and pasture spelling or leaving animals out of certain pastures for a period of time.

            He also notes direct application of chemical control such as spray-ons, pour-ons and dusts are options. However, there are no biological control methods for ticks.

Stable and house flies

            When it comes to pests affecting cattle in confined settings, Rochon says stable and house flies are some of the most economically important ones to pay attention to. 

            “The house fly is six to nine millimeters long, has three black stripes on their thorax and a cream-colored abdomen,” she explains. “They can transport pathogens but they are mostly just a nuisance.” 

            Comparatively, Rochon explains stable flies are smaller, at five to seven millimeters long and have black spots on the abdomen with a shiny, black, pointy mouthpart. She notes they have a very painful bite, which causes irritation and therefore reduces weight gain and feed conversion. 

            When it comes to controlling stable and house flies, Rochon notes sanitation is key. This includes destroying development sites, cleaning up spilled silage, ensuring adequate drainage, covering hay bales and laying traps. 

            “For biological control, producers can use parasitoid wasps or ducks and chickens,” states Rochon. “There are also direct chemical sprays, baits for house flies and residual wall sprays.” 


            “Lice can cause annoyance, extreme allergic reactions, hair loss, itchiness and stress in confined settings,” says Rochon. “This reduces weight gain and production.”

            She explains producers can check their cattle for lice by restraining them and parting their hair with a comb in certain areas.

            “Cattle biting lice feed on hair and skin and can be found across the topline of the back, on the face and on the top of the neck,” she says. “The long-nosed cattle lice feed on blood and can be found on the back, the shoulders and the neck.” 

            Rochon continues, “Little blue cattle lice and the short-nosed cattle lice also feed on blood. The little blue cattle louse can be found on the face and the short-nosed cattle louse can be found on the top of the neck and the brisket.”

            Rochon notes the cultural methods of controlling lice include inspecting and quarantining new animals, isolating infested animals, monitoring animals regularly and culling chronic carriers. She also mentions chemical control options include dusts, sprays and pour-ons. There are not biological control methods. 

            Hannah Bugas is the assistant editor for the Wyoming Livestock Roundup. Send comments on this article to

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