Lice significantly impact cage-free birds

Entomologist and study lead, Amy Murillo: “We didn’t expect to find skin lesions associated with chicken body lice, but we did. This has not, to my knowledge, been documented before.” Photo: Peter Roek

Recent research has disputed previous understanding that lice were not known to be a significant poultry pest in cage-free birds.

The study, carried out at University of California, Riverside, found that free-range birds were being infected by lice at much higher level than caged flocks.

The study’s lead author and entomologist, Amy Murillo, said: “We didn’t expect to find skin lesions associated with chicken body lice, but we did. This has not, to my knowledge, been documented before.”

Murillo studies pests of poultry and other livestock. To help detect mite infestations in chickens, Murillo previously led a team of entomologists, computer scientists and poultry specialists in creating a new insect detection sensor, which were worn on birds’ backs. The sensors for this study were used to monitor activity at 3 points in time – during a period where cage-free birds were not infested with lice, during a growing infestation, and during a full-blown infestation.

An increase in preening behaviour

The clearest signal of a lice infestation was an increase in preening behaviour, as the birds clean their feathers with their beaks. While preening is generally considered positive, too much of it could disrupt other healthy chicken behaviours.

“We found such a significant increase in infected flocks it makes us think they’re spending time preening when they might have been doing other things, like resting, eating, sleeping or laying eggs,” said Murillo.

A major increased in preening was detected even when the lice infestation was quite small. Murillo: “Just a few lice and you see a dramatic change in what the chicken is doing. They’re spending significant amounts of time trying to get lice off.”

Lice tend to live in places on the body that it makes it harder for hosts to remove. Chicken body lice tend to go under the wings, a place with warmer than average skin temperature that is harder for birds to reach. The lesions the researchers found there were actively breeding.

Managing lice in poultry

Strategies to mitigate lice are relatively limited as few insecticides can be used on poultry and it is difficult to apply pesticides to cage-free birds. But Murillo and colleagues have found promising results with the use of food-grade diatomaceous earth, a powdery substance made from fossilised remains of aquatic organisms.

“When chickens get it in their feathers, it disrupts the waxy exoskeleton of the lice. In other words, the diatomaceous earth makes it so the insects can’t prevent water loss. They then dry out and die,” notes Murillo.

Given the possibility that excessive preening may interfere with egg laying, Murillo would like to conduct a follow-up study: “Lice were not previously looked at as serious pests. Now that there’s evidence the lice impact the birds, I’d like to measure the economic impact of infestations,” she added.

The study, ‘Low levels of chicken body louse (Menacanthus stramineus) infestations affect chicken welfare in a cage-free housing system’, has been published in the journal Parasites and Vectors.