by: Heather Smith Thomas

Lice are a common winter problem in cattle. Heavy infestations of these tiny parasites rob nutrition from cattle just when they need it most. A lice-infested animal may lose weight and become more susceptible to disease. These external parasites are fairly easy to control, however, according to Dr. Ralph Williams, Department of Entomology, Purdue, University (Indiana).

“There are several species of lice that we see on cattle. One of the more common is the biting (chewing) louse. There are a couple types of blood-sucking lice—the short-nosed and long-nosed cattle lice. The short-nosed lice are probably more common. There are a couple other types that may be seen on cattle—the cattle tail louse and the little blue louse. Here in Indiana we most commonly see the cattle biting louse and sometimes the little blue louse. In other parts of the country the other types are also seen,” he says. Some cows may have several types at once.

The treatment you select depends on the type of lice you are targeting. Systemic treatments, especially the injected products, work very well for sucking lice but don't kill chewing lice. A topical product that spreads over the animal's body is needed for those.

Lice are winter pests, but if producers use insecticide ear tags during summer, Williams says this will help control populations of lice in the summer—even though lice populations are low and not of significance in warm weather. Lice spend their entire life cycle on the host. Unlike some parasites that spend part of their development elsewhere, cattle lice must be continually on cattle. Thus anything that you do to reduce their population or retard their reproduction will be helpful.

This is why the insecticide ear tags help, even though producers are encouraged to take them out at the end of the fly season—to help avoid the development of horn fly resistance as the effectiveness of the insecticide wanes after a few months.

“Insecticide ear tags by themselves are not considered lice control, but they do keep lice numbers down during summer. We've treated the cattle here at Purdue with insecticide ear tags every summer since 1977, and we rarely see lice problems in our cattle,” he says. Going into the fall, the cattle won't have the lice that would otherwise start to build up during colder weather.

The ear tags used on the Purdue cattle contain both organophosphates and pyrethroid insecticides. “These both spread on the hair coat effectively as cattle mingle. But fly tags shouldn't be considered as the primary means of preventing lice,” he says.

“Fall treatment using ivermectin has been shown to be very effective for sucking lice. This enables cattle to go into winter relatively lice-free. Even if there might be a few lice left on the animals, they usually don't become a problem again until late winter,” says Williams.

“For chewing lice, there are several brands of pyrethroid-based pour-ons available—that spread over the body via the skin oil and are very effective. There are also some good sprays, but spraying on a cold day can be a stress to the animal,” he says.

“Keeping cattle on a high plane of nutrition is the first major step, making sure they are healthy going into winter, and well fed,” he says. Healthy cattle in good body condition have more resistance to lice and are not as apt to carry heavy loads of parasites.

“Self-application devices can also help—for both chewing and sucking lice. There are some good commercial back-rub oilers and dust bags. If kept properly charged with insecticide, they are very effective since the cattle tend to rub on these if they are lice-infested,” says Williams. These can work well in feedlots or small pastures.

If late fall/early winter application doesn't keep the animals lice-free all winter, these self-application devices can take care of any lice that appear before spring. “These products spread well on the animals and kill both types of life. The pour-ons kill sucking lice and chewing lice, because the product comes in contact with both types. The systemic products like avermectins, moxidectin, and eprinomectin and also some organophosphates have systemic action,” he says.

“The pour-on treatments won't last all winter. If cattle start scratching and losing hair, the treatment should be repeated. It may take two or three treatments over the course of the winter. Animal behavior (irritation from lice) will tell you when they need to be treated again. The good thing about lice is that they are not known to transmit any diseases. The scratching can cause secondary infection (where the skin is broken) but no disease agents are spread by these parasites,” he says.

“ Signs of heavy lice infection include cattle itching, losing hair, becoming lethargic or going off feed,” says Williams. Cattle may spend more time scratching and itching than eating.

The systemic products that control both internal and external parasites are called parasiticides. “They need to be used with proper timing to target the specific parasite. A fall treatment will catch sucking lice and cattle grubs, and certain internal parasites. There has also been a pour-on formulation of ivermectin, but it is more effective for sucking lice than for chewing lice,” he says.

“I've seen cattle with very high numbers of chewing lice. Jack Lloyd, now retired from University of Wyoming, has done a lot of work with lice, and did many whole-hide examinations of cattle. It really surprised everyone, the number of lice that cattle can actually carry,” says Williams.

To check for lice, restrain the animal in a chute and look at certain areas such as behind the ears, on the dewlap, along the top of the neck, or around the tail head. “Parting the hair and looking at the skin will usually enable you to see them. Chewing lice are brown, while sucking lice have a blue tint because of the blood—and they also have elongated mouthparts that come to a point, for blood-sucking. With chewing lice, their head is as wide as their body,” says Williams. Lice are small but they can be seen with the naked eye, especially in good light.

“With use of insecticide ear tags and products like ivermectin, I haven't seen very many problems anymore with sucking lice—at least here in Indiana and the Midwest. They may be more problem on range animals that are not worked as frequently. People with small herds who don't do much with the cattle in the way of fly control, etc. may also see lice on their animals,” he says.

“Sucking lice are not as prevalent as they used to be, and cattle grubs even less. Ivermectin is totally effective against cattle grubs and since they have just a once-a-year life cycle they are easy to control. Lice, however, continue to reproduce year-round, though they build up more in winter because of the cold stress on the animals. Lice generally have a 3 to 4 week life cycle but the entire cycle is on the host. Eggs are attached to the hair, then the hatching nymphs and adults stay on the animal,” he says.

Lice are spread from one animal to another by close contact, rubbing up against other animals. Thus lice are more likely to be spread during winter when animals are grouped for feeding. “The eggs are somewhat resistant to cold temperatures but the nymphs and adults require the warmth of the body to survive. The nymphs and adults won't last long in winter apart from the host, but the eggs might continue to be viable for a couple of days,” says Williams. If egg-covered hairs were rubbed off on a fence or feeder, another animal might come into contact with them while rubbing on the same area, and could possibly pick up lice, but if weather is cold, the eggs won't hatch unless they are on an animal.

“If lice are seen on any individuals in a group of cattle, all the cattle in that group must be treated at the same time, or the untreated animals will spread lice again to the treated ones. Some animals will resist the effects of lice more than others (and may not be visibly itching, with hair loss), but will still have a few lice, so unless you treat them, too, you won't control the problem,” he explains.

Any new animals brought into the herd should also be treated, before you add them to the herd. “This is important, unless you have a history on those animals and they've just been treated for lice,” explains Williams.

“Lice control should be considered a year-round program, in conjunction with other parasite control efforts. Care must be taken to use proper dosage and timing for internal parasites or horn flies to avoid development of resistance issues, but to my knowledge we have not yet seen any pesticide resistance in lice,” he says.

“If you treat for lice in the fall and they become a problem again later in the winter, you can repeat the same treatment you used in the fall. If you don't treat in the fall, however, with a systemic product like ivermectin, you shouldn't repeat it later in winter if there's been any history of cattle grubs in the herd.” Treating with a product that kills grubs may cause potential damage to the host animal if these grubs die during winter in a later phase of their life cycle. The dying grubs can create swelling around the esophagus or spinal cord that may create a serious problem for the animal. A pour-on product for lice at that time would be safe to use, however.

“How readily the lice build up on cattle depends on nutrition levels going into the winter. Some individual animals also have a stronger, healthier immune system than others. Some have innate resistance while others may become carriers. This depends a lot upon the individual animals, and the breed. Any animals that have Zebu breeding (such as Brahman) will have some resistance to insects and any internal parasites. We looked at this in Oklahoma, with cattle ticks. Zebu or Brahman-cross cattle have more resistance to ticks than do Herefords or Angus.” They are a different species and came from a warmer climate that had insects year-round—and evolved with much more resistance.

Don't forget to BOOKMARK  
Cattle Today Online!