Bovicola bovis (old name)
Also known as Damalinia bovis (new name), red louse, and chewing/biting louse
Description
Bovicola bovis is a biting/chewing louse that parasitizes cattle worldwide, especially in temperate and cool climates, living on cattle of all types and ages. These lice belong to the order of Phthiraptera insects that live on many warm-blooded animals, but are host-specific, meaning this particular biting louse only lives on cattle. These lice are different from their blood-sucking cousins in the sub-order Anoplura in that they feed only by chewing on the skin. Cattle generally have both types of lice at the same time, however.
Biting lice feed on the upper layers of the skin, and sucking lice penetrate the skin and suck blood. Biting lice (Damalinia [Bovicola] bovis) are most common and cause the most itching and irritation, while sucking lice (Haematopinus eurysternus, Linognathus vituli, and Solenopotes capillatus) are more damaging; severe infestations can cause anemia. Cattle infested with lice will rub on any available surface, and chew or lick at themselves.
The head of the chewing/biting louse is dark red and the rest of the body yellowish-white. Even though these lice are smaller than some of the larger sucking lice (1/16 inch long, compared to ¼ inch long sucking lice) a close look at the infested animal will reveal the tiny parasites. If you part the hair on shoulders or head with your fingers, in good light, you can see lice with the naked eye, but a magnifying glass and flashlight makes them easier to see.
You can also see their eggs (nits) as small white, yellow or brown barrel-shaped specks attached to hairs. The eggs are pearly white when freshly laid, changing to pale brown as the embryos inside them develop.
If one animal in a group is carrying lice, the entire herd is probably infested to some degree. Biting lice can be found on the head, neck, back, and rear of cattle, and stay on the host animal; they require the host to survive.
Lice are always present; a few survive on cattle during summer. They increase their reproductive rate in cold weather; the time spread between egg-laying and the adult stage decreases, so there are more generations in a shorter time span. They thrive on cattle in winter when the hair is long and their tongues become less efficient at removing lice.
Cattle use their tongues for self-grooming; their rough tongue can pull off some of the lice that torment them. The tongue is covered with what looks like tiny combs and can remove lice when cattle have a short hair coat. It becomes more difficult when hair gets longer. The long hair gives lice protection and this is one reason they are more prolific in winter.
Numbers are usually low in summer because most of the lice are shed off in the spring with the winter hair. Lice also tend to leave the hottest areas of the animal in summer and don’t reproduce as fast. There may still be a few in areas on the animal where they can hide, such as between the hind legs, but otherwise the animal is relatively free of lice during summer.
Lice don’t survive well in heat. If a cow is standing in bright summer sunlight, her skin temperature may go up to 45 to 50 degrees Celsius (115 to 120 degrees Fahrenheit) which is outside the thermal tolerance of a louse. In hot weather, adult lice are dying off and not reproducing, so the population crashes. Lethal limit for adults and eggs is around 40 degrees Celsius (104 degrees Fahrenheit). Surviving lice retreat to cooler places on the animal.
Both sucking and chewing lice are generally present on the animal year-round, but numbers increase dramatically in cold weather, and also increase when they move into a herd that’s relatively unexposed—as when new cattle are brought in, or the resident herd gets lice across a fence from neighboring cattle. The naïve cattle can get high numbers very quickly.
The life cycle of a louse is 20 to 40 days (shorter in cool temperatures). Eggs laid by the female are attached to hair and hatch in 5 to 14 days. After the nymphs emerge (looking just like adults, only smaller) they feed on the host and go through 3 molts, then become egg-laying adults. Maturation from egg hatch to adulthood takes about two to three weeks. Once the louse is mature, the female lays eggs, laying 1 to 4 eggs every two days—and may lay eggs for up to 9 or 10 weeks. The population of biting lice is 95 to 99% female and they can reproduce without mating.
Dislodged eggs, when hair is rubbed off on a fence or feeder, can still hatch, and may still be infective for up to a week--for any cattle that come in contact with them. If you put new cattle in a corral where lousy animals have been recently rubbing, lice can be transmitted to the healthy cattle.
All three stages (eggs, nymphs and adults) are present at the same time on any given animal, and though direct contact is the primary means of transmission, eggs and nymphs can be transmitted by use of brushes or other equipment, or contact with feeders and fences where infested animals have rubbed.
Biting lice do not transmit diseases, in contrast to sucking lice that may spread blood-borne diseases.
Signs
Itchiness, licking themselves, rubbing, hair loss, abrasions, restlessness, hindered appetite (too busy rubbing and licking to eat), sometimes weight loss.
Causes
For all ages of cattle, stressors such as confinement and high stocking density, poor feed, and underlying health issues contribute to susceptibility and degree of infestation.
Some animals, either due to poor immune function or other factors are more vulnerable to extensive lice populations, and have higher numbers, even in summer. They transmit lice to the other cattle in the herd. These carrier animals always have more lice, and some ranchers cull those individuals, so they can’t spread lice. Over a period of years, however, a carrier may gain some resistance and no longer harbor such high numbers.
Cattle with lice readily pass them to herdmates through direct contact, since cattle are social animals. Carriers serve as a continuing source of infestation for the herd. Young animals and older undernourished cattle usually have the heaviest infestations, and the latter can become or carriers that reinfest a herd every winter. Lice are spread by contact from carriers to other cattle, and from cows to their calves.
A carrier is usually an older cow that always harbors an unusually high number. These cows have an immune problem and don’t develop resistance like other cattle, and their lice are not killed as readily. Even when treated, some lice on a carrier go ahead and lay eggs before they die. Also, the cow is carrying so many that the treatment does not kill them all. There is swift re-infestation on that animal, and she serves as a source of lice for the rest of the herd, necessitating further herd treatments through winter.
Cattle normally develop some resistance to lice after exposure. There is usually quite a difference between severity of lice infestation between a young animal and an older animal that has encountered lice before. The young, naive animal will develop a high louse population upon first exposure, whereas the older, more immune animal will have fewer numbers.
Increased body contact between animals aids spread of lice (when cattle are congregated for feeding, or brought into corrals for weaning calves, preg checking and vaccinations).
Prevention
There’s no way to prevent lice, since there’s no vaccine to help cattle build resistance, and producers haven’t tried to select for lice-resistant cattle.
To keep lice to a minimum, it helps to avoid overcrowding, and make sure animals have good nutrition—and no underlying health conditions. Treating the herd at appropriate times of year (at the start of cold weather, before lice numbers explode during winter) can help prevent heavy infestation in winter.
It also helps to treat all animals on the farm at the same time, and move them to a new pen or pasture. When treating a group of cattle, do not mix them with untreated cattle afterward, or the untreated ones will spread lice to the treated animals.
Stock trailers, chutes, and other areas that lousy cattle have contacted should be cleaned and treated with an appropriate premise spray if they are going to be used again for cattle, or stand empty for about 10 days, to make sure there are no viable lice. Lice on hair that’s been rubbed off lousy animals may still contain lice or eggs that may live for a few days, to reinfect other animals that come into contact with them.
Treatment
Lice control is most crucial in cold climates. There’s not as much problem with lice in warm areas, and stockmen in some southern regions do not bother to treat for lice. Lice populations are never as high in a warm winter climate as in cold climates.
Many producers treat for lice in the fall when they put cows through the chute for preg-checking and vaccinations and wean calves. Systemic products (macrocyclic lactones like ivermectin and moxydectin) are often used. Some of these are pour-ons and some are injectable. The injectable formulations kill sucking lice but not the biting/chewing lice (which are usually more common).
Systemic products kill sucking lice and worms, since they feed on blood, but are not effective against chewing lice. It is beneficial to follow the macrocyclic lactones later with a pyrethroid product to kill chewing lice. For effective treatment, you need something that gets both biting and sucking lice.
Always assume that any new animal brought into the herd is carrying lice. New animals should be isolated and treated, whatever time of year they are brought in, before being put with the herd. Some products for lice have a two-treatment protocol (a follow-up treatment to kill the ones that hatch from eggs that were unaffected by the first treatment), and new animals should be kept isolated until they’ve had both treatments
A variety of compounds effectively control cattle lice, including synergized pyrethrins; synthetic pyrethroids cyfluthrin, permethrin, zetacypermethrin, and cyhalothrin (including gamma- and lambda-cyhalothrin) (for beef cattle only); the organophosphates (rarely used anymore because of dangerous side effects), tetrachlorvinphos, coumaphos, and diazinon (beef and nonlactating dairy cattle only); and the macrocyclic lactones ivermectin, eprinomectin, and doramectin.
There are several pour-on formulations of 5% permethrin/5% piperonyl butoxide, 5% diflubenzuron/5% permethrin, and gamma-cyhalothrin, labeled for season-long lice control (~3–4 months) on beef and dairy cattle. Although both amitraz and spinosad are effective against lice, the last cattle products containing amitraz were removed from the U.S. market in 2014. Spinosad formulations for use on cattle were discontinued in 2010.
Certain Brahman and Brahman-cross cattle (and some dairy cattle) have organophosphate hypersensitivity and should not be treated with any organophosphate product.
Ease of application and reduced stress to animals has made pour-on methods of treatment popular (compared to dips, sprays or injection). Self-treatment can be accomplished using proper insecticides in back rubbers, oilers, dust bags, and ear tags. Grooming alone—such as rubbing and scratching—can help keep lice population down, but when winter hair coat gets really long, it reduces effectiveness of the tongue to pull lice off. The tongue is a great grooming device, but with a thick hair coat the animal can’t get to the lice that are right down on the skin. Back-rubbers and other devices for them to scratch on can be a help.
Treatment of meat and dairy animals must be restricted to uses specified on the product label. All label precautions should be observed. Appropriate meat and milk withdrawal times must be observed. In most countries, regulatory agencies specify tissue residue limits of insecticides, and regulate insecticide use on livestock. All regulations are subject to change, so current local laws and requirements should be determined before treatment.
Producers generally don’t need to treat in late winter if a few lice show up on cattle in late March or early April, because the population won’t grow large at that late date. Even on untreated cattle, lice numbers are dropping at a rapid rate by that time.
A basic treatment program consists of dosing cattle in late fall to knock down the population growth curve so that by January there’s not a massive outbreak. No matter what you use for treatment, never under-dose. Always treat at maximum level. If you don’t kill all the lice on an animal, that animal serves as a source of lice for the rest of the herd and can spread lice to the ones you just treated--and you may see high levels of lice again before winter is over.
Re-treatment is recommend later in winter (February), if lice become a problem. A topical product like an oil-based pyrethroid spreads through the hair coat and usually has enough residual activity to give control into spring. These work well as a follow-up treatment.
There are indications that chewing lice are becoming more common than biting lice, since the macrocyclic lactones used as injectables only kill sucking lice. Chewing lice seem to be the biggest problem now; they survive treatments a little better than sucking lice do. By mid-winter the cattle are itching and miserable again.
The pour-ons have good effect on chewing lice, because these products tend to distribute over the body. There may be locations on the body the drug never reaches, however, such as between the hind legs and in the armpit area of the front legs. This residual population could proliferate and eventually cover the body again after the drug no longer has an effect.
Louse control is also a matter of timing. If you treat too early, the hiding lice have a chance to rebuild populations. If you treat later in the fall or wait until early winter, there’s less opportunity for them to rebuild. October-November is usually a good time. Many ranchers treat too early, if they vaccinate and preg-check cattle in September.
Even though many cattle producers treat for lice, it seems that cattle become re-infested more quickly than they did in the past. There are hints that some of the products might be less effective today—either because lice are becoming resistant or the products were not used properly or in proper dosage.
Researchers in the UK, working with pyrethroids on chewing lice, found some lice that were actually resistant to pyrethroids. Many people have been using pyrethroids as a backup for treatment after using the macrocyclic lactones--to kill any residual lice or prevent a new buildup. If these products are not as effective as they once were, producers won’t have the ability to knock the lice down as well.