Cattle lice in New Zealand

Provided by Schering Plough Animal Health.

Lice are small, flat-bodied insects with legs modified for grasping hairs. Four species of lice are known to infest cattle in New Zealand, three 'sucking' and one 'biting' (more correctly chewing), but only two are of significance.

The sucking louse (Linognathus vituli)

The sucking louse, sometimes called the long-nosed or blue cattle louse, is the most common variety in New Zealand. Adults are 2-3mm in length, with a long, narrow head and a yellowish-brown body that appears bluish due to ingested blood. They are usually found on protected areas of the skin and are generally more prevalent on younger dairy stock.

The biting louse (Bovicola bovis)

The biting louse, also called the red louse, is found on cattle of all ages. Its mouthparts are adapted for chewing and it feeds on debris on the skin such as dead skin cells, secretions and bacteria. This parasite is often found in colonies, which sometimes appear as circular, crusty lesions, but may spread all over in winter.

Dual infections with these lice species are common and the occasional animal may also be allergic to them, but loss of production is the main issue. It is commonly believed that lice cause weight loss, but experimental evidence does not support this in New Zealand.

Lice irritation leads to scratching, rubbing and licking that can damage the skin. The resulting damage becomes apparent as 'light spot' and 'fleck' defects on tanned hides that, along with secondary scratching damage, have a considerable cost for New Zealand's leather industry.

Typical louse life cycle

The louse has only three stages in its three-to-five-week life cycle - egg, nymph and adult. Females lay, on average, one egg per day, which cements to the host's hair, and hatches 8-21 days later. The nymph moults three times as it grows into an adult. The whole process occurs on the animal as most lice die very rapidly in the environment, with only a very few surviving a week in even the most favourable conditions.

Lice are spread by prolonged close contact between animals and are incredibly host specific - the four New Zealand species recorded are only found on cattle. Numbers often peak in winter when climatic conditions and the animal's coat favour survivability. As winter is often a time of feed restriction and close contact, these stresses may depress immunity and facilitate spread.

Finding lice

The most likely place to find lice is on the muzzle, neck, shoulder, escutcheon and, in the case of biting lice, the end of the tail. In heavy, winter infestations lice may be found anywhere, though they are often difficult to pick out on black cattle.

Eggs are also hard to see and the empty shells, left after the nymph has hatched, are often all that is found and are easily mistaken for scurf. The tiny nymphs are also difficult to detect.

Distinguishing the adult lice types is relatively easy. The biting louse has mouthparts adapted for chewing, so its head is broad and flat, whereas the sucking louse's head is narrow and pointed for sucking.

Biting lice appear brown with a number of closely spaced stripes across the back. Sucking lice appear blue/black (due to blood seen inside the body wall) and have no stripes. The nymphs of biting lice are much paler than both adult biting lice and the nymph of the sucking lice.

Prevention

Cattle in good condition carry fewer lice than those in poor condition; therefore feeding level has a significant influence on louse numbers. Spread is also greater in situations were there is repeated close contact, e.g. during transport, on feed or loafing pads, during yarding prior to milking, and suckling after calving.

Treating lice

Lice can be treated at any time of the year but many farmers prefer totreat in the autumn or early spring. Careful consideration must be given to milk and meat withholding when selecting a product as they vary markedly with respect to withholding periods. Numerous systemic or non-systemic product options are available.

Systemic products

Systemic products are absorbed into the bloodstream after either topical (pour-on) application or injection. These systemic products can be divided into two families, the macrocyclic lactones (ML) and the organophosphates (OP).

The macrocyclic lactone products control internal as well as external parasites. The active ingredients in ML include ivermectin, abamectin, moxidectin, and eprinomectin. Importantly, there is a difference between injectable and pour-on ML products. The injectable products fully control sucking lice but have only partial efficacy against biting lice. The pour-ons perform well against both species.

Organophosphate products only control lice. Examples of actives found in OP products include propetatamphos and temephos. Most OP products are pour-on formulations and all have a milk-withholding period.

Non-systemic products

Non-systemic products spread around the skin surface of an animal and are not absorbed to any significant degree. All are from the synthetic pyrethroid family of active ingredients with the most common example being deltamethrin.

These products treat lice and some prevent the landing of nuisance fly, a significant pest in some dairy herds. They do not control internal parasites.

These products are generally applied as a pour-on, but as they spread around the body application technique is very important. The general recommendation is a continuous band from between the ears to the base of the tail.

Written by Dr. John R Moffat BVSc
Veterinary Technical Advisor
Coopers
Schering Plough Animal Health