by Tamara Scully

When cattle are confined in outdoor spaces, several ectoparasites are of primary concern. These parasites live on the outside of the host’s body, causing discomfort, avoidance behaviors, reduction in weight gain and feed efficiency and potential illness. For outdoor confined cows, several types of flies and lice are the peskiest of these parasites.

“You need to assess your population” before you can implement IPM, said Kateryn Rochon, Ph.D., University of Manitoba, in a recent Beef Cattle Research Council webinar. “What do you have? What’s causing a problem?”

Behaviors such as rubbing, stomping or bunching together typically indicate a pest is present. Positively identifying the pest by sight, if possible, is recommended. If the pest is not seen, analyzing where on the animal there is irritation, which indicates a problem, can be useful.


Two types of flies are of primary concern with confined outdoor cattle: stable flies and house flies. Both prefer wet or damp areas, and are particularly attracted to manure and manure residue. Both are small, like to rest on vertical surfaces and can cause production losses.

Pupae (the pre-adult stage of these flies) can be found around hay rings.

“You expect house flies and stable flies in confined production,” Rochon said. “They develop really well in manure that is coming from animals fed concentrated feed.”

Distinguishing features of the house fly include a yellow abdomen and four black stripes on the thorax. They move a lot of pathogens around, and can be seen in large numbers, but are primarily a nuisance.

Stable flies are biting flies with sharp mouth parts. They are a bit smaller than house flies, with black spots on their abdomens. Their bite is painful, and they can reduce gain and feed efficiency. They can be seen clustering on the front legs of cattle.

Ten flies per leg will cause both gain and feed efficiency to decrease. In confined systems, it’s easy to see the front legs of cattle, so this visual assessment is easily utilized. Rochon recommended that treatment start when stable fly counts on front legs number four per leg.

“At very low numbers, you can get an 8% reduction in gain,” Rochon said. “You want to keep your threshold low.”

Prevention should always come first. Keep the animal environment clean by removing manure regularly, picking up spilled silage and keeping areas dry to cut down fly problems. Address any drainage issues and cover hay bales. Traps for both flies are available.

In one study, a 50% reduction in stable flies per front leg was seen when cleaning of manure was performed every two weeks versus not cleaning at all during summer months.

Biological treatments for stable and house flies include parasitoid wasps, and even the presence of chicken or ducks in the environment.

“Really, sanitation is key if you want to control stable flies,” Rochon emphasized. “You have to do that biological control with sanitation. You can’t just release [wasps] and hope that they do the work. Ducks and chickens really do like to eat maggots, and they’ll go and peck them out. They are more effective than traps,” although they may not be practical in larger herds.

Applying residual insecticidal sprays on walls and vertical surfaces can also reduce stable and house fly populations. Baits can be used for house flies. Direct sprays have limited effectiveness against stable flies as the cows’ legs get muddy and the product will rub off quickly, but will provide some relief.


There are four species of lice – one sucking and three biting – which plague outdoor confined cattle. Animals will rub, lick and scratch at areas where lice reside. There can be damage to the hide, areas of hair missing and skin rubbed raw. Animals become very stressed and waste energy scratching, and production losses can result.

“It’s really essential to be able to see the problem” and to identify the species of louse causing it, Rochon said. Mites, which are not visible to the naked eye, can also cause similar behaviors, as can nutritional issues.

Lice are visible to the naked eye. Use a comb to part the hide in problem areas: the dewlap, cheek, muzzle, eye, withers, topline and tailhead. Combined numbers of lice at all sites indicate the level of infestation, with more than 50 being severe, and less than 10 considered minimal.

Each species of lice found in confined outdoor cattle environments – long-nosed, short-nosed, little blue and cattle biting louse – prefer to reside on certain regions of the body. The cattle biting louse, which can cause anemia, is typically found on the top of the back. Long-nosed lice prefer the back, shoulder, dewlap or face. Short-nosed lice are found at the top of the neck, dewlap, brisket and the ear. The little blue lice gather around the face.

Prevention begins with cultural control. Isolate and inspect any new animals admitted to the herd. Regularly monitor for the presence of lice, and cull any chronic carriers. Bulls tend to be chronic carriers. It is not known why some animals are quite attractive to lice, but it is suspected to be either genetic or tied to their individual immune systems, Rochon said.

Lice do not fly or jump, and can only move from animal to animal through contact. In winter, when conditions tend to be more crowded, the population can increase rapidly. There are no biological controls for lice. Chemical controls include dusts, sprays and pour-on products. For sucking lice, systemic products are effective.

Taking Control

Resistance is a concern, and can occur when products using the same active ingredient, or the same mode of action, are used over time. Chemicals belonging to the same group need to be rotated with the use of chemicals from other groups. Ear tags can also be problematic, as the dose of chemicals decreases over time, potentially allowing resistant populations to occur. Pests with short generation times are more prone to becoming resistant to chemical treatments than those with longer generational spans.

All treatment strategies need to be evaluated, and ongoing monitoring of pest populations will provide useful information regarding effectiveness. Reassess as needed to keep pests below threshold levels. Thresholds can be set for animal welfare as well as for loss of production and economic harm.

The economic threshold (the point where not treating pests causes economic damage) fluctuates depending on production methods. Because most economic thresholds were configured decades ago, they may not make sense today. Changes in production practices, as well as in the genetics of the animals themselves, can impact pest threshold levels, Rochon said.

No matter the pest, control requires properly identifying it first. Reducing ectoparasites requires using more than one type of control method – cultural, biological and chemical. Controls must be applied at the right time, and in the right place. If applied too soon, the product will be ineffective. Knowing the threshold level of the targeted pest should guide decisions. Label directions need to be followed for best results and to prevent issues.

“Make sure that methods that you are using are appropriate for what you are trying to fight. The right timing – the right product – delivered properly,” Rochon said.