Controlling Lice in Beef Cattle

By Heather Smith Thomas

Lice are a common winter problem in northern climates--with cold weather and short winter days.  Summer heat, sunlight, and short hair make it more difficult for lice to survive and multiply; there are not very many lice on cattle during the summer.  Their numbers increase dramatically when weather is cold and cattle have long hair for lice to hide in; the life cycle speeds up and there are a lot more lice on the host animal.

To give an example of how temperature affects lice populations, David Boxler, Entomology Extension Educator, University of Nebraska says that when the ambient temperature is 78 degrees, an animal’s skin in direct sunlight can reach 100 degrees F.  “This inhibits lice, their eggs, and egg production.  When skin temperature exceeds 100 degrees, lice start dying.  At 125 degrees all species of lice will die within an hour.”

There are always a few lice that survive through summer on the host animal, hiding in protected areas of the body, but most of them die or do not reproduce readily.  “They go into a stage of estivation.  They are still there, but dormant and not feeding or reproducing.  Then as temperatures drop, their populations increase,” says Boxler.

Dr. Nathan Erickson, Western College of Veterinary Medicine, University of Saskatchewan, says control of lice is more challenging some years, partly due to weather patterns.  “Many of the products for killing lice on the animal are only effective for about 50 days.  If it’s a long winter, cattle may need to be treated again before spring,” he says.

“If we treat cattle too early, ahead of cold weather, we don’t get a very good kill because the lice are not active in warm weather.  If it’s still warm in late fall, we may not have much lice emergence until effectiveness of the product has already worn off.  The product is no longer present on the animal when it needs to be there,” says Erickson.

Boxler says attempts at lice control often fail simply because cattlemen treat too early, before the numbers start to increase.  “In our area, we generally wean calves in late September or early October, and ranchers use that opportunity to work the cows and calves to vaccinate and control internal parasites, cattle grubs and lice.  This is generally too early to treat for lice.”  

The population of lice is still very low and you might be wasting your money to treat cattle at this time.  Some lice survive the treatment and when weather gets cold later they quickly multiply.  Lice don’t reproduce in warm weather but thrive in the cold.

“If daytime temperatures are still in the 50’s and 60’s, it’s too early.  I suggest looking at the cattle very closely in late December, to check for lice.  Tell-tale signs are itching and rubbing, hair loss, etc.  Bring a few animals in and restrain them in a chute so you can part the hair and look for lice.  I use a halogen light and a magnifying glass, especially with dark-colored cattle.  There are basically two types of lice—sucking lice and chewing lice.  The chewing louse is hard to see in a dark hair coat.  The sucking lice are easier to see because they have a bluish color and tend to stand out.  Also they are not moving around and hiding in the hair,” says Boxler.

“The chewing lice are more active and their populations can increase dramatically because they can reproduce asexually; the females don’t need the male.  You may see a huge explosion of that species in a very short time,” Boxler says. This may be another reason that some herds tend to have more problems with chewing lice than sucking lice, because their numbers can increase so quickly.

Treating Cattle For Lice
For best results, all animals should be treated at the same time.  “If we miss an animal, or don’t get enough product on some of the animals, or a group of treated cattle are put with untreated cattle, those untreated individuals will spread lice again to the treated cattle,” Erickson explains.

Application technique is also important. The product needs to be applied properly, and in a correct dose for the size of the animal.  If it’s a cold day, the product may gel and won’t go through tubing, If it is being applied from a jug with tubing to the applicator gun.  “It may become slush rather than liquid, and we may not get as much product onto the animal.  Some of it may roll off.  If weather is wet or cattle have snow or moisture on their backs, this will interfere with proper absorption.”  If you get the product applied and then it rains or snows immediately after, this may also reduce efficacy.  It pays to watch the weather and try to do the treatments during dry weather and not extremely cold.

There are two types of lice, and this can also be an issue.  The sucking lice are easier to control; a systemic product can be used because it is absorbed into the bloodstream and the sucking lice pick it up.  The biting/chewing lice are not affected by a systemic product because they do not suck blood; they merely feed on skin.  They also move around more.  “To control chewing lice we have to make sure we apply the topical product along the entire topline, from the neck/withers all the way to the tail head, to improve chances for contact, since those lice are active (and must come into contact with the product on the animal).  Sometimes this can be challenging, to get the product all along the animal’s back,” says Erickson.  

If a person simply puts it all in one area on the back, it may not be as effective.  It takes more time to put it all along the topline and some people get in a hurry (especially if it’s being done along with many other tasks such as preg-checking, vaccinating, processing feedlot cattle, etc.).  The oil-based products tend to ooze down through the hair and cover more area, so if you get it spread all along the topline there is more total coverage.  Select the right product for your situation, and pay attention to label directions.

The non-systemic products are synthetic pyrethroids. Most products require 2 applications 14 days apart, to get the newly hatched lice, since these products don’t kill the eggs.  There is one product that contains a combination of a synthetic pyrethroid and an insect growth regulator that will kill the eggs.  Boxler says this is a good rescue product if your other treatments have failed.

“There are some new products that specifically state they need skin contact, which means it needs to get under the hair and onto the skin,” says Erikson.  “Follow directions for dosage as well, and don’t under-dose.  Some people have larger cattle than they realize (and are not giving a large enough dose); not everyone has a set of scales.”

Often the cattle are deloused at the same time they are being processed and vaccinated, and people are doing so many things at once that occasionally they miss an animal or only apply a partial dose.  “Sometimes when I am preg-checking and people are vaccinating and applying the delouse product, the person doing the delousing might not be paying attention when spraying it on—and half the dose goes onto the side of the chute or on the ground, or sometimes on me!  It’s important to make sure it is actually getting onto the animal!”  Take time to do it correctly.

It’s also good to monitor cattle afterward to make sure the treatment worked.  “If you see some cattle itching and rubbing, or hair loss, you might want your veterinarian to look at those animals to see if it truly is a louse problem, or something else.  If it is a louse problem, you need to treat them again as quickly as possible, before they have too much hair loss,” he says.  Once they’ve rubbed out hair, it takes a long time for it to grow back in, and they’ve lost some of their insulation against the cold; those cattle will need more feed to maintain themselves and keep warm.

If cattle start rubbing and have scruffy hair coats Boxler recommends checking them.  “There are other things that can cause rubbing and poor hair coat; it could be due to mite infestation, poor nutrition or photosensitivity.  It’s wise to look at them and see what the problem is,” he says.

It is important to keep a good level of nutrition through winter.  Lice tend to multiply more quickly on animals that are lacking in nutrients and don’t have a strong immune system.  “Studies have shown that cattle with higher nutrition levels generally have fewer lice.  Those animals are less severely affected by lice than the animals on just a maintenance ration.  Nutrition is a key factor in helping manage lice populations,” he explains.  If it’s a hard winter, make sure cattle have adequate nutrition for maintenance, growth, pregnancy and keeping warm, for good health.  If animals are cold and losing weight, they tend to have less resistance to lice and have more lice than well-fed animals.

Sometimes there are a few individuals in the herd that have more lice than others (often called carriers), and they spread lice to herdmates.  Some ranchers cull those individuals because they seem to have more lice problems every year.  They carry more lice through summer and the lice population increases on them more dramatically in fall and winter.  “We suggest culling those animals and getting them out of the herd,” says Boxler.  Otherwise they spread lice to the others, even after they’ve been treated.  This susceptibility to lice seems to be partly genetic and a person might not want to keep daughters from that cow (or bull).