Beef cows are rugged creatures. They are able to withstand the extreme cold and variable weather experienced here in the Northeast due to a rumen that provides heat from fermentation, a thick hide and a heavy hair coat. However, this heavy hair coat is also a refuge and perfect environment for a thriving lice population. The result is that when the population reaches the economic threshold level, cattle lose some of the insulation value provided by hair.
Cows that cannot keep warm during the wintering period suffer reductions in feed efficiency, milk production, disease resistance, weight and fertility. Lice are also a Beef Quality Assurance (BQA) issue, as they reduce the value of the hide, which is of concern to packers and the leather industry. These production losses occur though these external parasites and the associated loss in animal performance are not always obvious.
The good news is that unlike flies, lice spend their entire life cycle on the animal, making control much more successful. The bad news is that in most cases the cattle will need to be treated at least twice within a two-week period to maintain control, and any new animals introduced will need to be free of lice or they can be a source of re-infection.
- Little red cattle chewing louse (Bovicola bovis)
- Long-nosed sucking louse (Linognathus vituli)
- Short-nosed sucking louse (Haematopinus eurysternus)
- Little blue sucking louse (Solenopotes capillatus)
- Although there’s some size variation among these the first four species of lice, all of them are small insects that reach a maximum size of about oneeighth of an inch.
- Female lice lay their eggs, known as nits, by attaching them to hairs with a strong glue to prevent them from falling off.
- The nits can be seen on heavily-infested animals as white specking on the hair coat.
- Ideally, a headband light or hard hat-mounted light should be used so that both hands are free to work with the animals.
- The neck, shoulders and tailhead should be inspected on each animal by parting the hairs and estimating the numbers of lice present per square inch.
Life cycle explained
Eggs. Female lice lay their eggs, known as nits, by attaching them to hairs with a strong glue to prevent them from falling off. The nits can be seen on heavily-infested animals as white specking on the hair coat. The hard shell of the nit protects it from most hazards, including insecticide treatments.
Nymphs. Eggs hatch into nymphs one to two weeks after being laid. Lice have a simple metamorphosis; therefore, the nymphs resemble the adult lice quite closely except for their smaller size. The nymphs feed on host animals in the same manner as the adult lice.
Adults. Knowing the species of lice and how they feed on cattle is important in understanding how to control them.
Chewing lice (Damalinia bovis). This is the most common species and has a yellow-brown appearance. As its names implies the chewing louse does not suck blood but uses its mouth parts to rasp away and eat hair and skin. This is the most common form of lice found in the Northeast.
Sucking lice. There are three species that suck blood: the long-nosed cattle louse (Linognathus vituli), the short-nosed cattle louse (Haematopinus eurysternus), and the little blue louse (Solenopotes capillatus). Sucking lice have mouth parts specialized for penetrating animal skin. They spend most of their time with their heads firmly attached to the skin. Sucking lice often take on a darker appearance than chewing lice as they become engorged with blood.
Although there is some size variation between the four species, they are all small insects reaching a maximum size of ⅛ inch. As stated previously, they are permanent parasites, meaning that their entire life cycle (four to six weeks) occurs on the animal.
Lice are most commonly found on the animal’s neck, back, hips and tailhead.
When to treat
Some external parasite treatments control lice and grubs (Table 1). If using these combination products, treatment can be applied any time in September or October but should be completed prior to November 1. Beginning about this time there is the increasing possibility of damaging reaction to the toxic substances released from grubs killed along the esophagus or spinal cord. While the incidence of cattle grubs has greatly declined with common use of these pour-on products, I did see a severe reaction in a group of feeder cattle about five years ago. Therefore, strictly observe this cut-off date, especially with purchased cattle with no known history of grub treatment.
Pour-ons should be applied along the back line from shoulder to hip. Whether using a pour-on or injectable product, both are dosed according to weight. Overdosing is expensive and does not increase effectiveness. Underdosing leads to parasitic resistance.
For maximum effectiveness, treat only when the animal’s hair coat is dry. Heavy rains within a few hours after application may reduce effectiveness. However, there are some products that claim to have weather-resistant properties. Calves under three months old should not be treated.
Treatment with combination products should not be performed with other stressful major management operations, e.g., live virus vaccination, castration, dehorning or when animals are sick or being transported. This includes the stress of weaning. Application can be safely combined with pregnancy examination.
There are products that can be used at any time of the year for lice control, because they do not kill grubs (Table 1). Generally, permethrins are cheaper than combination pour-ons, and don’t select for resistant worms because they do not target internal parasites. Application methods include dusts, sprays, pour-ons, back rubbers and dust bags. Regardless of product or application method, to maintain complete control of lice, animals need to be treated thoroughly at 10- to 14-day intervals to kill the eggs and nymphs, which hatch after the initial treatment. Assuming that all animals are properly treated, two to three applications are usually sufficient. Any animals introduced after the herd has been treated should also be treated twice before being introduced to the general population.
When using any of these products, wear gloves and avoid using in a closed space to prevent breathing volatile fumes.
All of the combination and many of the lice-only products have a withdrawal period. You must read the label and follow withdrawal to avoid sending animals to slaughter with violative residues.
Lice are relatively easy to control compared to other cattle pests. However, a plan for monitoring the population and a proper handling system are required. This is not only good for the performance of your herd, but is the responsible and right thing to do as caretakers of cattle.
Geden, C., Steinkraus, D. and D. Rutz, 1989. Cattle Lice. Dairy IPM. Dairy/Field Crops. 102GFSDI-1. http://vet.entomology.cals.cornell.edu/extension-publications
Woodson, F. E. 1980. Control of grubs, lice and flies in beef cattle. Cornell Beef Reference Manual. Fact Sheet 3300.