RIVERSIDE, Calif. – Researchers at the University of California Riverside are uncovering that lice are significant pests to poultry, particularly birds raised cage free.

Amy Murillo, assistant professor of entomology at UC Riverside, became interested in lice affecting poultry as a doctoral student.

“We surveyed backyard farms in southern California where we have really urban areas and really rural areas, and no matter where we went, we saw a high incidence of lice,” she said. “It was really interesting because, in commercial settings, fowl mites are the primary problem.”

Understanding the parasites that impact cage-free poultry is increasingly important as many states enact new legislation that prevents animals from being caged. Some states, including California, Washington, Oregon, and Nevada, have production and sales bans on eggs from caged poultry. Other states, like Ohio, have suspended new permits for caged-layer operations.

Murillo and her team acquired chicken body lice from a commercial farm and infested birds to study how lice impacted cage-free poultry. They also studied a group of uninfested chickens as a comparison group. Three times during the study period, the team assessed the welfare and behavior of chickens. Data was collected using a specially created device that sits like a backpack on the back of the bird that can sense and collect information about the birds’ behaviors.

“I think the most important thing we learned was that we did see changes to the chickens’ behavior in terms of how they’re spending their time,” Murillo said. “They spent a lot more time preening when there were lice on the birds, and I think the interesting part of that is that it wasn’t very heavy infestations – in one of our trials, we had very low louse numbers, and we still saw that impact.”

Although Murillo’s team didn’t directly study how lice could impact production, she said that when birds spend much more time grooming, they spend less time eating and moving around, which could affect their physiology. Ultimately, more studies are needed before the economic impact of lice is understood.

Murillo said the second big takeaway from the study was that skin lesions were associated with lice infestation. The type of lice that impact chickens is known as chewing lice, a parasite thought to only chew or feed on feathers or fur. Other lice are known as sucking lice, associated with feeding on blood.

“The general thought around chewing lice is that they’re only feeding on feathers or fur, so they’re not really negatively impacting the host as much. You might have a bird that’s lost some feather coverage or looks lousy,” she said. “But we actively saw blood in the lice and these lesions, so that leads to more science – like why are they chewing on the blood? What do they get from it?”

Adding to the mystery of chicken body lice is the fact that it is currently unknown how the parasites are transferred to outdoor poultry, Murillo said. In some cases, feed stores where poultry are purchased are infested with chicken body lice. However, some producers Murillo spoke with hatched their birds from eggs and raised them without any interaction with another flock.

“We don’t know how (lice) are getting onto these properties,” she said. “Another area of research I’m very curious about is (understanding if) wild birds are playing a role in moving lice.”

Interestingly, lice seem to be a problem specific to cage-free poultry. But Murillo doesn’t think it’s purely the practice of cage free that has contributed to infestations. Looking through old veterinary textbooks of the late 1800s and 1900s shows that researchers and producers at the time noticed a lot of mite pests and lots of lice, Murillo explained.

“I think [lice] have been around a long time, and I think as we’ve intensified farming and put birds indoors and changed the management, it’s become either less noticeable or easier to deal with the problem,” she explained.

When birds are in cages, spraying for mites using different chemicals is common. Murillo speculates that some of these chemicals could have also been effective at ridding birds of lice, so lice might not have been a noticeable pest commercially in caged facilities. Also, spraying cage-free birds for pests is challenging, another reason lice may be more prevalent in these populations. Murillo also noted that many insecticides are now banned, which makes the management of pests more difficult and less straightforward.

Murillo and her team have tested one management strategy on a small scale: food-grade diatomaceous earth mixed with washed sand. This mixture can be put into bins or plastic swimming pools, and the birds will come to the areas to dust bathe, lifting the material into their feathers and over their bodies. Diatomaceous earth destroys the exoskeleton of lice, killing them. 

Next, Murillo and her team are interested in understanding how widespread the problem of chicken body lice is for producers and the economic impact of the issue. Then, the team will work toward developing strategies to mitigate lice.

“We want our research to be applicable to what’s happening on the farm,” she said. “My goal ultimately as a researcher is to better understand the economic risks of ectoparasites and find management strategies that are going to work in different (production) systems.”