Parasites can affect weight gain in cattle

The lives of cattle can be far from placid if they are bothered by parasitic flies, ticks and mites, which also affect animals’ production and weight gain.

Thirteen different parasites affect beef cattle in Canada and if they reach high numbers and are not properly addressed, they can cause stress, weight loss, lower milk production and injury. Some can also carry pathogens that cause anaplasmosis, epizootic haemorrhagic disease, bluetongue and pinkeye.

By definition, a parasite makes its living at the expense of another organism. An ectoparasite is one that lives outside the host but causes harm by feeding on the host.

Shaun Dergousoff, an Agriculture Canada entomologist and research scientist, provided this list of cattle parasites during a recent Beef Cattle Research Council webinar:

    • Chewing lice
  • Sucking lice (four species)
  • Ticks (dog, wood, winter)
  • Biting midges (no-see-ums, gnats)
  • Mosquitoes
  • Horn flies
  • Stable flies
  • Horse flies
  • Deer flies
  • Black flies
  • Face flies
  • House flies
  • Mange mites

Some are difficult to tell apart, said Dergousoff, so before taking control measures to protect animal welfare, prevent disease transmission and forestall any human complaints about excessive flies, for example, it’s important to identify the specific pest.

“The goal is to reduce harm to the livestock, whether it’s a nuisance, or injury or actual disease, and reduce production losses,” he said. “It doesn’t necessarily mean that we’re going to try and eliminate the pest but at least reduce numbers so that none of these things happen.”

An integrated management approach is recommended, said Dergousoff, with preventive measures to keep pest numbers down combined with treatment options. However, information on economic thresholds that would trigger control measures is lacking, he added.

The first step is to identify the pest and estimate numbers. That can be done by observation or use of traps, combined with watching the animals to gauge the level of irritation cattle are experiencing.

The second step is to evaluate options for control and treatment, whether biological, cultural or chemical. Examples of biological control are predators or parasites of the pests. Cultural control might involve reducing sites favourable for pest development, for example. Sanitation, water and manure management are in this category.

“Chemical control is of course a common and important method of controlling pests but really you need to consider the timing of application, the mode of application… and the class of insecticide that’s being used.”

Third is to implement the most appropriate control methods and fourth is to monitor the pest population after treatment.

Dergousoff noted some pests are a problem mostly in grazing systems and others have a greater effect on cattle in confined feeding systems.

Horn flies, for example, are a problem in pastures and rangeland.

“These are one of the most damaging economically for cattle producers.”

Horn flies like fresh, undisturbed manure and standing water. They can sit on animals for long periods, and generally cluster on the head, shoulders and back.

Horn flies are about five millimetres long, charcoal grey and have a V-shape. They can bite their host as much as 40 times a day, becoming a constant irritation to cattle and affecting their behaviour and growth.

Dergousoff said some studies showed an 18 percent reduction in weight gain among yearlings with heavy horn fly pressure.

Control methods include walk-through traps and disturbance of dung pats, encouraging dung beetles and various insecticide sprays, pour-ons and oilers.

There are three types of ectoparasite ticks in Canada that can also affect cattle on rangeland: American dog tick, Rocky Mountain wood tick and the winter or moose tick.

In the case of the three species common in Canada, control measures include physical removal of the ticks, keeping cattle away from favourable tick habitat and direct application of insecticides.

Kateryn Rochon, associate professor of entomology at the University of Manitoba, focuses her work mostly on parasites in confined feeding systems. House flies and stable flies are among the most bothersome in those environments, she said, and lice can also present problems.

The flies’ affection for manure and wet, decaying feed, can make control a challenge in feedlots.

House flies are mostly an annoyance but stable flies bite and in sufficient numbers will affect cattle weight gain and feed conversion.

“Stable flies really like legs…and so that’s how we assess the abundance of the population.”

Rochon said 10 or more flies per leg can mean and eight percent reduction in feed efficiency. The threshold for treatment is about four to five flies per front leg.

Sanitation will help with control. Clean up spilled feed and employ good drainage.

Traps can help, and parasitoid wasps are available but Rochon said more than one method of control should be used. Direct sprays aren’t effective against stable flies because the insects favour the animal’s legs, which get dirty and wet so chemical rubs off easily.

Lice are another problem in confined systems, said Rochon. Infestations cause cattle to rub, lick and scratch, leading to hair loss, stress and wasted energy.

Different types of lice prefer different parts of the animal, which is a guide to the type of lice that is causing the irritation. The cattle biting louse likes the topline of the back, the long-nosed cattle louse prefers the shoulder, neck, dewlap and face, while the little blue cattle louse favours the face and the short-nosed cattle louse congregates on the top of the neck, dewlap, brisket and ears.

Chronically infested animals should be culled. Treatment with dust, sprays and pour-ons is available but it’s important to treat at the right time and change the mode of action in insecticides to avoid insect development of resistance.

“You want to avoid anything that has too much of a decreasing concentration of insecticide over time,” said Rochon, and that is a problem when it comes to ear tags.

Ideally, a different mode of action would be used every time cattle need to be treated.


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