Delousing products generally require two treatments about three weeks apart to kill all the lice that hatch out from the eggs that weren’t affected by the first treatment.
“There is one new product that does seem to work if you can only pour cattle once,” according to Dr. Dave Barz, a veterinarian in Parkston, S.D. “It’s called Clean-Up II and contains a pyrethroid, which kills adult lice, plus an insect growth regulator that keeps the nymphs and newly hatched lice from maturing.”
It has enough residual effect to thwart the lice that hatch out after the treatment.
“We’ve been using that for several years and are seeing better results,” he said. “This might be something to try if cattle are continuing to have lice problems after traditional treatments. In our area, if you start to have problems, the company you bought the product from will usually give you more, so you can get them re-poured. That’s been their guarantee, at this point in time.”
Many ranchers in his region pour cattle with an avermectin product at turnout time to kill internal as well as external parasites, and again in the fall at roundup to kill lice.
“Most of these cattle are moved with trucks now, so a lot of them get poured as they come off or get on a truck. Any time you are handling the animals, you can think about using a pour-on,” he says. “We’ve talked about rotating the pour-on products, using different ones different years, but we are seeing lice resistance to all of them. The only one that is really helping us right now in terms of thwarting a new hatch of lice is the Clean-Up II.”
Some feedlots now are using injectable and pour-on products at the same time — a full dose of each — and in those groups of cattle we haven’t seen as much problem with lice recurring.
“Hopefully we are getting a better kill, and maybe more residual effect,” Barz says. “We can’t scientifically explain it, but it seems to help.”
For best control, it’s very important to treat all of the animals at the same time, with a proper dose, and not skip any.
“This is why the treatments work so well in the feedlot, because the whole pen is treated. There are no animals skipped, that would re-infest the treated animals,” he says.
The important thing is to have a good lice control program in terms of when to pour the cattle, and how best to break the life cycle. Lice are a bigger problem when animals are confined and grouped together (in terms of spreading lice to one another) as for winter feeding, calving, etc.
“A few years ago, some ranchers decided to use natural products rather than insecticides,” Barz says. “The old way, before we had insecticides, was to use the back-rubbers with oil on them, so the cows’ hair was oily, which tends to deter the lice. But these are only spot treatments. Also, in every herd it seems like there’s a cow or two that act as carriers; they have heavier infestations and may have lice even after treatment, spreading lice to the other cattle.”
Lice are often a problem on young calves.
“If the cow has lice, some are readily transferred to the calf through direct contact, and the lice population explodes on the calf because it is small and thin-skinned,” Barz says. “If you at them closely, some of the lighter-colored calves will almost be black with lice. This is why controlling lice on cows is important, so they won’t spread lice to their calves. Otherwise we have to pour the calves fairly soon also, to decrease their lice populations.”
Some lice are always there, in any herd of cattle. They multiply most readily on the young, the weak, the old and any thin, sick ones. Any animal that is compromised tends to have more lice.
“If an animal is weak, and parasites are taking blood, that animal is more susceptible to pneumonia, scours and other secondary infections,” Barz says. “This is why lice control is so important — not just because the cattle are scratching/rubbing the fence down. Lice are nibbling away at the potential profit from your herd!”