Lice are small, flat-bodied insects with legs modified for grasping hairs. They cannot survive off of the animal for more than a few days. Sucking lice, with their narrow, pointed heads, are blood feeders. Biting lice feed by scraping material from the skin and base of the hairs. The eggs, or nits, of both types are glued singly to hairs and hatch in about two weeks. The nymphs, or immature stages, resemble the adults but are smaller. They mature in about three weeks. Adults live two to three weeks and females lay about one egg per day.

Infestations of biting and sucking lice have been associated with reduced weight gains and general unthriftiness of cattle. The economic impact of these small insects has been very difficult to assess. However, it appears that an average of 10 or more per square inch are necessary to have a significant effect. Lice are most abundant on animals during the period of greatest winter stress. Many veterinarians and producers believe that losses occur and some cattlemen will treat animals for lice just for the improved appearance that results.

The potential for severe, direct losses caused by sucking or biting lice is low. Moderate to heavy infestations add to the impact of cold weather, shipping stress, inadequate nutrition, or harm from internal parasites or disease. The interaction between low levels of both lice and intestinal nematodes can reduce weight gains by more than 8%. The energy that lice "steal", coupled with other factors, can have a severe impact on animal health. Manifestations can be anemia, slow recovery from diseases, poor gains, or general unthriftiness.

Crowding or bunching of the animals at this time of year provides many chances for lice to move from animal to animal. Reduced light intensity appears to play a significant role in louse numbers on animals but nutrition, general health, immune system response, and weather are important factors.

Monitoring lice numbers
Heavily infested animals can be diagnosed easily. The most obvious signs are rubbing and clumps of hair falling out. There can be raw spots from constant attempts to groom or scratch areas where lice are abundant. Crushed lice and their feces, blood, and serum from wounds can give cattle heavily infested with the shortnosed louse "greasy" appearance. Feeding by biting lice produces a skin reaction in which the hair becomes loose. Eggs of the biting louse are laid on fine hairs and the coat takes on a matted appearance. While other factors can cause restlessness and scratching, the presence of lice can easily be confirmed and eliminated relatively quickly.

In severe infestations, sucking lice are densely packed, creating characteristic quarter-sized black or blue-brown spots. They are less likely to move or be disturbed by skin searches. Biting lice apparently do not like to be crowded so they are usually not found in tightly packed clusters. They are active and will move readily if disturbed. Count and record the numbers and species of lice that are found; mixed infestations are common. Large lots of cattle are rarely given the close attention required to detect these small insects, especially when populations are at very low levels.

Light infestations of these external parasites are easy to overlook unless animals are inspected carefully. In these cases, the lice are usually confined to spots in preferred areas on the animal. Examination of five, one inch square areas on the face, dewlap, neck, back and base of the tail of each animal would be a conservative protocol. Look first for nits, then part the hair carefully to look for lice. Both biting and sucking lice feed head down with their abdomens pointed out. Identify the species present and record the number found per square inch at each site. Mean numbers per square inch can be categorized as less than 5 - very slight, 5 to 10 - slight, 10 to 20 - moderate, 20 to 50- severe, more than 50 - very severe.

Lice persist over the summer months on reservoir animals. About 1 to 2% of the animals in herd can be chronically infested, with lice moving to other animals in the fall and winter. Older cows or bulls are the most likely reservoirs. The longer, thicker hair and massive neck and shoulders of bulls makes self-grooming difficult, apparently grooming can reduce lice numbers to some extent. During the hot summer months, a few lice may survive out in the ear tips where temperatures do not reach lethal levels. The chances of detecting these carriers is slim because of the amount of time it would take to search thoroughly to detect them.

Common Cattle Lice
The life cycle of biting and sucking lice have the three stages associated with incomplete metamorphosis- egg, nymph, and adult. Single nits or eggs are glued to the hair shaft. The three nymphal stages resemble the adults except they are smaller. Measurements given for the different lice species are for adults. Development time is directly related to temperature so life stage values in the following sections can vary by several days. The entire life cycle is spent on the host.

SUCKING LICE
Shortnosed cattle lice are the largest of the common species; adults are about 2/10 of an inch long. They are easily recognized by the gray-black body and relatively blunt head. There are noticeable conical bumps along the sides of the body. Shortnosed cattle lice are found more frequently on mature animals where they prefer to feed along the top of the neck and around to the dewlap and brisket. As numbers increase, these lice can be found from the base of the horns to the base of the tail.

Females attach white to brown eggs to hairs at the rate of one to four each day for about two weeks. Eggs hatch in about two weeks and the immatures, or nymphs, reach the adult stage in about two weeks. Adults live 10 to 15 days.

The longnosed cattle louse has a slender, pointed head and a narrow bluish black body. It is more commonly seen on calves and dairy stock and rarely occurs in large numbers on mature animals. This louse is usually most abundant on the dewlap and shoulders but will spread over the entire body when animals become heavily infested. As the weather warms in the spring, and numbers drop, they are usually seen last on the shoulders. Females deposit an egg a day during their life. The complete life cycle takes about 3 weeks.

Little blue cattle lice are found most often in small clusters on the muzzle, neck, and dewlap of mature cattle. Clusters of lice around the eyes cause heavily infested animals to look as if they are wearing glasses. Females lay one to two eggs a day and the hair to which an egg is attached is typically bent at an angle. The eggs hatch in about 10 days and the nymphal stages require about 11 days. Little else is known about the details of the life cycle.

BITING LICE
The cattle biting louse is easily recognized by its large, bluntly triangular head and a yellow-white body with dark bands. Eggs hatch in about 10 days and development to the adult takes about a month. Adults may live for up to 10 weeks. Biting lice are most commonly found in colonies or "patches " at the base of the tail, shoulders, and top line of the back. Skin around colonies of this louse can have the appearance of mange lesions.

by Lee Townsend, Extension Entomologist