Lice pose a problem for cattle producers during the winter months

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 may become more susceptible to disease. 

Many stockmen in regions with a cold winter climate try to control lice populations on cattle.

Standard treatment

Lee Townsend, Extension entomologist with the University of Kentucky, says there’s not much that’s really new for lice control. 

“The standard treatments are still the pyrethroid insecticides, which are effective against all types of lice,” he says.

Townsend says that diligent lice control can effectively get rid of lice in most herds. He cites a European study that looked at attempts to eradicate both sucking and chewing lice in herds and says that elimination was successful in 85 percent of the study herds, or 28 out of 33 herds. 

“The strategies they used included application of insecticides, utilizing two treatments about three weeks apart, culling any animals that appeared to be carriers or reservoirs of lice and quarantine or treatment of any new animals brought into those herds,” says Townsend.

Reoccurance

Lice were seen again in five of the 28 herds within three to six months after treatment and were back in nine of the 28 herds within a year. 

“Factors associated with the re-infestation of lice included purchase of livestock or bringing lice-infested animals into the herd, failure to treat newly introduced animals or missing one of the two treatments and mixing of treated with untreated cattle due to fencing problems,” explains Townsend.

If a producer doesn’t make sure that all the animals on the farm get treated, or fails to follow up with the second treatment, there will be residual lice population on some animals, and they will pass lice to the rest of the herd. 

“Giving the two treatments three weeks apart is an important key. The products that are being used don’t work against the egg stage. The first treatment should get most of the lice that are active – the adults and nymphs,” he says. 

The eggs on the hairs will survive, however, to hatch later.

If producers fail to treat even one or two animals with the second treatment, eggs on their hair coat will hatch and could provide enough lice, over time, to be a source of reinfestation for the entire herd. 

Infestation

“Signs of infestation may be subtle at first. Producers may not notice lice until there’s a large population – and then the cattle will be rubbing and scratching,” he says.

“If there are several hundred lice per animal and the rancher only gets 90 percent control with a certain treatment, this still leaves a fair number of lice to start the infestation coming back again,” says Townsend. 

The systemic products may kill most of the blood-sucking lice, for instance, but don’t give much control of chewing lice. This makes it harder to get rid of lice in a herd.

One of the things that contribute to lice problems is that there’s not a really clear-cut economic indicator for treatment – and some producers don’t take the time or go to the expense of treating their cattle. 

Treatment options

Some of the methods that allow cattle to self-medicate with back rubbers or dust bags can help control lice in late winter. 

A fall treatment, such as a pour-on or a systemic product, will often reduce lice numbers for several months but then they start building numbers back again before spring. 

“The self-treatment methods can supplement lice control in a manner that eliminates labor and handling of the cattle again,” says Townsend.

Producers just need to figure out ways that will work best in their own operation and facilities. 

“There’s enough differences in how people handle cattle and what they do with them during winter that there is no one answer to lice control. Keeping problems in mind and having a plan to deal with lice within your own management system is the important thing,” he says.

Treatment selections

Some animals seem to have better resistance to lice infestation than others. There are always some animals in the herd that never have very many lice, and some individuals that have less resistance and act as carriers. 

“Younger animals tend to have heavier infestations, which may mean that they have not yet developed much resistance to lice. Those are the animals that are often sold off the farm or ranch,” says Townsend. 

A producer buying stocker calves or replacement heifers is thus buying animals with greater potential to be infested, with less resistance to lice.

“If the producer has to make a decision regarding which animals to treat and which ones not to treat, they should prioritize regarding the ones that are more likely to be infested due to their age or background,” he explains.

“Attention to detail is important regarding lice control. This will keep the rancher from having to do additional treatments, or running into infestations that they thought they had dealt with and managed,” says Townsend.

Heather Smith Thomas is a correspondent for the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.

SIDEBAR:
Cost of lice

“There are some studies that show lice reduce milk production or affect gains on young cattle, but there also a number of studies that show moderate numbers of lice don’t have a very big impact,” University of Kentucky Extension Entomologist Lee Townsend comments. 

“If there’s not a well-recognized cost associated with lice infestation, it’s harder for producers to justify the expense of delousing their cattle, especially when profit margins are small and they are trying to save money – along with the labor and time to bring animals in for treatment,” he says.

In cold weather, however, when cattle are rubbing and itching instead of eating, or losing the insulating protection of their hair coat by rubbing out patches of hair, lice control is probably cost effective. 

“Produces are paying for those lice, in terms of the extra feed required by the cow. The animal has stress from cold weather, stress from lice and a few other things, and it all adds up,” he explains. 

“Ranchers are probably looking at a number of separate small stresses that by themselves might not make a lot of difference, but together they do,” explains Townsend.

“The reputation of the cattle producer – as having healthy animals that have had their vaccinations, deworming and parasite treatments – is another consideration,” Townsend continues. “If a rancher purchases calves or replacement heifers from another producer, they want to be confident that the animals won’t be bringing an unwanted problem into their own herd.” 

It helps buyer confidence, to know that the animals have been on a good health program that includes external parasite control. The animals also look better if they have a healthy, full hair coat rather than raggedy bare patches from rubbing due to lice.