Lice are a common problem that can cause economic losses, reduce weight gain and lead to a general unhealthy appearance.
“When I hear the word ‘lice,’ two pictures always come to mind; one is me as a kid, lined up with my friends on a cold Idaho morning, waiting for the school nurse to tell us we couldn’t share hats anymore,” says Kirk Ramsey, DVM and Neogen professional services veterinarian. “The other is my cows in winter, rubbing themselves raw against the feed wagon while I beg them to move so I can finish chores in the snow.”
Different scenes, same reminder: As long as mammals have existed, so have lice.
“The reality is that when it comes to lice, ‘an ounce of prevention is worth a pound of cure,’” Ramsey says.
Application Timing and Best Practices
Timing lice control is what makes prevention difficult. One of the most common wintertime complaints cattle veterinarians receive is asking why cattle still have lice even though they were treated the last time they were worked.
“Most spring calving herds do all their herd work in the fall. This means cattle are vaccinated, checked for pregnancy, wormed, and often lice prevention is applied in October or November,” Ramsey explains. “The problem with that logic is that, in many parts of the country, very few lice will be present at that time, and it may be a month or two until the weather deteriorates enough for lice to really be a problem. To reduce risk and create control measures, understanding the life cycle of lice and targeting application times are paramount.”
To achieve seasonlong control, Ramsey says you have to break the life cycle. If treatment is completed too early in the fall, it’s possible only adult lice will be eliminated, not the eggs they laid.
“Producers will not have that seasonlong effect because the life cycle was not broken,” Ramsey says. “Where you will really find success is using a product labeled for lice that has an insect growth regulator (IGR) to help break the life cycle of the louse.”
Selecting a formula that includes an IGR, such as diflubenzuron — which disrupts nymph maturity — minimizes handling time and labor costs.
He adds, “It’s key to note here that most products include an adulticide, which treats adults, but the adulticide will not affect nymphs or eggs.”
When selecting an insecticide, be sure to consider its active ingredients and mode of action.
“It is important to also consider that insecticide resistance may be present in ectoparasite populations in various geographic locations, so a chemical control strategy that rotates between classes of insecticides is recommended,” Ramsey says.
Breaking the Life Cycle of Lice
The key to breaking the life cycle is to first understand how lice develop. First, you have eggs — also referred to as nits — which develop into nymphs within 10 to 20 days, which then transform into adults.
Adults live from two to six weeks, with the female laying 30 to 60 eggs in their lifetime. It may not seem like that massive of a number, but it is a decent number when you’re considering that this is just from one female, and you are never just going to have only one in an infestation.
Signs of Lice
Clinical signs of lice in cattle can include intense itching, patchy and flaky skin, hair loss, lethargy, decreased gain and weight loss.
“Cattle can also get to the point of anemia, when they become very ill looking, and their hair coat will look very poor,” Ramsey explains. “One study from the University of Nebraska, as well as other studies, indicates heavy lice populations may reduce weight gain by as much as 0.21 lb. per day.”
Types of Lice
Ramsey explains there are two types of lice: the sucking louse and the chewing louse.
“In its simplest form, chewing lice feed off skin debris and hair, to some extent, which causes itching,” he explains. “Sucking lice feed on blood, causing anemia and pathogen transmission. The sucking louse can be a biological vector for diseases like Anaplasmosis or Theileria.”
Lice can be present on the skin surface at the base of the hair; they also have a predilection for the face, neck, shoulders, back and tailhead of the animal.
To learn more about lice prevention and control, visit your local veterinarian or visit Neogen.com.
