Because lice often are inconspicuous, many dairy producers do not detect them until their cattle begin to show hair loss from the animals’ grooming activities.
But by the time the infestation has progressed to this stage, populations of lice are already well above economic injury levels—and treatment becomes very difficult owing to the large number of lice involved.
Effective management of cattle lice below economic injury levels requires sampling of apparently healthy as well as noticeably “lousy” animals for the presence and relative number of lice.
Such surveillance should be conducted every two to three weeks throughout the fall, winter and spring months.
Lice can be monitored easily with a flashlight and a little practice. Sampling involves carefully inspecting sections of skin on a representative sample of animals in the herd, either 10% or 15 animals in each group: mature cows, heifers and calves.
The best regions to inspect are the head, neck, shoulders, back, hips and tail. If sampling indicates that the cattle-chewing louse, Bovicola bovis, is the dominant species present, assessment of the neck and tailhead alone is sufficient to detect most infestations.
Treatment is recommended when counts average more than five lice per square inch.
Management: Cultural Control
Producers can save on the cost of insecticide treatments for lice by adopting cultural control practices.
First, replacement animals brought into the herd should be isolated and carefully inspected for lice before they are allowed to mingle with the rest of the herd.
Second, careful and regular monitoring for lice can detect problems before an infestation gets out of control.
Third, housing calves in hutches will reduce infestations on these valuable replacement animals by up to 90% without any insecticide applications.
Management: Chemical Control
Many insecticides and application procedures are effective for managing lice. As with any insecticide application, it is essential to consult the label to ensure that the insecticide is registered for use on dairy cattle and, if so, whether it may be used on lactating animals.
Before selecting an insecticide, consider how it can be applied to meet individual needs and production practices.
There are several categories of application methods: self-application devices, whole-animal sprays, pour-ons and dusts.
Self-application devices such as dust bags must be placed in areas where animals will contact them frequently and treat themselves with repeated, small doses.
Whole-animal sprays have the advantage of ensuring good coverage over the animal’s entire body. Severe louse problems on mature animals are most common in winter, and it generally is wise to avoid soaking animals in periods of cold weather.
Applications with foggers and mist blowers can overcome this problem. With these types of applications, a small quantity of concentrated pesticide is propelled as an aerosol that contains very small spray particles. The concentrated aerosol can then be applied evenly over the animal’s body, greatly reducing the amount of liquid used.
Another method of application is pour-on insecticides, in which a small quantity of pesticide is poured down the backline of the animal.
A popular application method for lice is dusting by hand. Dusts are easy to apply, require no mixing and can be used year-round.
Insecticides must be used properly to achieve satisfactory control of lice. Many louse-control products require two treatments, two to three weeks apart. The second treatment is essential to kill newly hatched lice that were present as eggs at the time of the first treatment and, therefore, were not killed.
Failure to make the second treatment in a timely manner will create problems requiring subsequent treatments.