Now you see 'em. But mostly you don't. And that makes diagnosing a lice problem in your cattle a bit challenging.

However, says Jack Lloyd, professor emeritus in entomology at the University of Wyoming in Laramie and one of the leading authorities on cattle lice, more than likely you have a subclinical lice population in your cattle herd. Given the right conditions, populations can build during the fall, then explode into an infestation during the winter months, causing grief for cattle and cattle producer alike.

Trouble is, nobody knows exactly what those conditions are.

A lot of factors are at play, Lloyd says, such as changes in diet, immune response, day length and sunlight. And there has been speculation and study for years on what triggers an outbreak. “Well, it's not one thing. It's probably a complex of things.”

But one thing's for sure — if you get an outbreak, you've got a problem. “Lice affect weight gains, they affect the quality of the hide, animals do a lot of damage to facilities because they rub a lot,” Lloyd says. “Even with moderate levels (of infestation), we see some effect on weight gains.”

In a Nebraska study, heifer calves on a growing ration with a lice infestation of 10 or more/sq. in. gained 0.21 lb./day less than noninfested heifers. In a study Lloyd conducted, he found about a 10% difference in weight gain in favor of yearlings treated for lice control.

Know thy enemy

There are five species of lice that are a concern in the U.S., and they tend to be found on different parts of the animal.

The cattle biting louse tends to be the most abundant species on cattle. It has chewing mouth parts and is found mostly on the topline along the back and in the withers. “You'll see animals with bare areas,” Lloyd says. “If you look closely, they're quite active lice with little bars going across the body.”

Then there's the sucking lice. The little blue cattle louse, for example, favors the head. “You'll see little clusters of blue up on the facial areas, mostly,” Lloyd says. “On the cheek, on the muzzle, around the eyes. Occasionally, in very heavy infestations, you will see clusters in the dewlap area.”

The long-nosed cattle louse is very common on calves, though it occurs in older cattle as well, Lloyd says, and it can be found all over the body. “This is one louse that doesn't have a specific spot, although sometimes they'll be found in the clusters of the little blue louse.”

Then there's the short-nosed cattle louse. “It shows sort of a seasonal distribution. In the summertime, when the herd has them, you can find them up in the ears. But in the wintertime, they spread down onto the face and the dewlap area. They're easy to see. Because of their larger size, you'll see little gray spots,” Lloyd says.

A fifth species, the cattle tail louse, exists in the Gulf Coast areas of the U.S. and Southern California. It's different from the other four species in that it tends to be more of a summertime pest and only exists in the southern states.

Outside of the tail louse, cattle lice are primarily a wintertime pest, says Wes Watson, veterinary entomologist at North Carolina State University at Raleigh. And the four major species generally are a bigger problem in the colder northern states than in the warmer southern states.

That may be because lice are one of the few external parasites that spend their entire lives on cattle. “The louse actually has claws adapted to grasp the hair,” Watson says. When cattle slick off in the spring and summer, many of the eggs or nits fall off and there's a lot less habitat left for the adults that hang around.

But a few will hang around and a subclinical population will make it through the summer. When fall rolls around and temperatures begin to cool, conditions become right for lice populations to increase.

Trouble is, lice infestations aren't uniform among animals, Lloyd says, which can make diagnosis difficult. “There's tremendous variability between animals as far as susceptibility goes. And their reaction to the lice varies a lot, too.”

Some animals will rub and scratch considerably when they have what would be considered a light infestation. “And next to them will be an animal with what you would consider a heavy infestation and it's not rubbing at all.”

But generally, rubbing and scratching are the early warning signals that lice are a problem. “You begin to notice some problems with some animals,” Watson says. “They are itchy, their hair coat is rough and doesn't look good.”

Control

Lice are easily controlled either with pour-ons or by spraying with an insecticide. “In general, for all species of lice, the pour-ons, especially the systemics, have been effective,” Lloyd says. In Wyoming, lice populations always seem to increase the first week in December, he says. But if cattle are treated with a pour-on during the fall work-up, it prevents populations from building in the fall and exploding into an infestation during the winter.

If grubs are a concern, Lloyd says it's important to treat early with a systemic to avoid a reaction in the cattle with grubs in the esophagus and the neural canal. But generally, Watson says, treating in October will provide sufficient control until spring.

Occasionally, Lloyd says, one or two animals in the herd will experience a resurgence in the spring before they slick off for the summer. “Just go out and re-treat them with a pour-on,” he says.

If you receive new cattle in the fall or winter, consider inspecting them visually, says Justin Talley, Extension entomologist with Oklahoma State University at Stillwater. If you part the hair and look at the skin in the areas of infestation — the withers, shoulders and back — you may see lice on the skin. “If they are lousy, treat them right there, before you introduce them into your herd. It's a whole lot easier to treat those new animals than having to treat your whole herd” later on, Talley says.

Lice infestations are a hit-or-miss proposition. But if you notice signs of a lice problem this fall and winter, timely control will prevent them from being more than just a minor irritation.