Ectoparasites: What’s eating your beef?

by Tamara Scully

Parasites are pesky problems which live on or near a host, and do so at the host’s expense. Whether the parasite is an ectoparasite – living on the outside of the host body – or an internal one, it will take a toll on your cattle.

There are 13 types of ectoparasites that bother beef cattle. All cause similar symptoms, and figuring out which parasite is bugging your herd can be complicated. Lice – both chewing and sucking types; biting midges; mange mites; mosquitos; ticks; horse, horn, deer, black, face, house and stable flies are ectoparasites of cattle.

“They can be very difficult to tell apart, even when you look at them closely,” said Shaun Dergousoff, PhD., Agriculture Agri-Food Canada. Dergousoff presented information on ectoparasites in a webinar for the Beef Cattle Research Council, www.beefresearch.ca

No matter which of the ectoparasites is present, they have negative effects on the animal host. They might do direct damage, blood feeding on the host and causing health issues. In other instances, the parasites increase cattle stress due to their persistent presence on or around the animals, which can change cattle behavior.

When ectoparasites are present, feed intake can decrease, as can milk production. Injury can also occur due to the animal’s rubbing/biting/licking or other attempts to stop the parasite’s effects.

Vectors of illness

Not only do ectoparasites cause cattle irritation and result in production losses: they can also act as vectors and introduce other disease causing organisms into the herd. Pinkeye, epizootic haemorraghic disease, bovine anaplasmosis, bluetongue and eyeworms are all vectored by cattle ectoparasites.

“The pest is actually a host to these pathogens, and you get amplification of these pathogens, and then they can transmit to another animal,” Dergousoff explained. “Or you get mechanical transmission… where you spread the host to one animal to another just by carrying them.”

Some cattle ectoparasites are also vectors to disease causing pathogens which can infect humans. West Nile virus, Lyme disease, babesiosis, Powassan encephalitis, anaplasmosis and Eastern equine encephalitis can all be transmitted, via cattle ectoparasites, to humans.

Integrated Pest Management strategies

“Pest control can be an important consideration in beef cattle production. The goal is to reduce harm to the livestock. It doesn’t necessarily mean we are actually going to try to eliminate the pest, but at least reduce numbers.”

Integrated Pest Management (IPM) involves preventative and treatment measures – biological, culture and chemical – to keep pest numbers down, and below the economic threshold where money is lost. Prevention is the first step, but when parasites are present, treatment thresholds are based on animal welfare and economic loss considerations.

“The decision to treat can also be based on an economic threshold, with the number of insects affecting the livestock actually causing economic losses; or too much harm to the animals,” he said. “There’s a real lack of information for economic thresholds.”

IPM requires multiple steps. Identifying the pest and assessing its population level is the first step. Traps and monitors can capture specimens for identification purposes and to determine the scope of the parasite problem. Animal behaviors can also hint at what parasite might be causing harm.

Once the pest is identified, cultural measures to reduce environmental issues – particularly sanitation around manure and water sources, spilled feed and fence lines – are needed. These areas are conducive to pests laying eggs, and threshold populations are likely to develop if left unchecked. Biological controls will target the parasite, and are predators or parasites of the cattle ectoparasite, and will therefore reduce its population.

“Biological and cultural control methods are really important, because they are meant to reduce the frequency and the intensity of pest population outbreaks,” which can then eliminate or reduce the need for chemical control methods, Dergousoff said.

Chemical control includes animal application in the form of dust bags or oilers, application sprays, or sustained release methods such as ear tags. These can have a long- or short-term efficacy, must be targeted to susceptible pests, and utilized at the right time to impact these pests. Environmental treatments are also available, such as baits, foggers or area sprays. There may be withdrawal periods involved before re-entry, or before animal harvesting.

The effectiveness of the IPM program involves assessing whether the number of pests decreased, and determining whether the pest numbers rebound, or if re-treatment is needed. This will help to inform future decision-making.

It’s also important to continually monitor off-host environmental conditions. Understanding the parasite lifecycle can help manage the environment and keep pest pressures low. Environmental sanitation can control multiple parasite problems.

Pastured cattle

Different animal production systems can be plagued by differing varieties of parasites. Dergousoff discussed IPM approaches to two common parasites which can plague pastured cattle and cause serious economic and animal welfare concerns.

Horn flies can plague grazing herds and are one of the most economically damaging pests. If cattle are bunching together in pasture, with lots of tail swishing, stomping and ear flicking, horn flies are probably present. These flies are five millimeters in size, charcoal gray, and require fresh manure and standing water. They can stay on the animal for long periods, and cluster primarily on the head, shoulders and back. “V” shaped wings are an identifying factor. They bite up to 40 times per day. More than 200 flies per head is the treatment threshold.

Calf weaning rates are reduced by eight percent in weight gain for every 100 flies on average. Yearlings, too, show reduced weight gain at this infestation rate.

Treatment for horn flies depends upon the life cycle stage. Adults lay eggs in fresh dung. Dung beetles are a biological control method. Cultural control includes traps, as well as disturbance to the dung patties by pastured poultry. Chemical control via ear tags, dust bags, sprays or feed-through control is effective.

Ticks are disease vectors, and can cause paralysis, blood loss and irritation. The tick population is changing as warmer temperatures are causing ticks to expand their ranges into more northern regions. Cultural control includes decreasing vegetation, leaving pasture fallow to prevent tick re-infestation and removal of ticks from animals. Biological controls are few, but some birds will consume ticks, and fungal pathogens are being researched. Chemical controls, directly applied to the animals and not environmentally, is effective.

No matter the production system, ectoparasites can cause problems throughout the year. While some pests are present year-round, such as lice, they are not always a problem, as their intensity can increase at different times of the year. But animals can remain carriers, and the pest will be transmitted through the herd. Pest pressures can change with temperatures, or with the time of day.

“The profile of parasites will change throughout the year. When it seems like the problem has gone away, that doesn’t necessarily mean the pest is gone,” Dergousoff emphasized. “You do end up with production losses with some of these external parasites. Pest control can be an important consideration in beef cattle production.”

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