The HAF RESEARCH data show that last winter there was an increase in the number of cases of lice seen by HAF RESEARCH vets. Lice populations are highest in winter and lowest in summer. There are two main reasons for this. Firstly, housing significantly increases the rate of transfer of lice between cattle. Secondly, low light levels and cooler skin temperatures are associated with increased louse activity. The denser winter coat and cooler weather thus favours lice survival.
The effect of lice
Lice cause irritation of the skin. This leads to biting, scratching and rubbing by affected cattle. These cows may also damage fences, trees and buildings while rubbing
The effect of lice on the production and growth rate of cattle has been the subject of much research but is still is a matter for continued debate. Their effect on the skin of cattle is probably best understood. Lice are probably the primary cause of “light spot and fleck”, a blemish visible on the hide of cattle which down grades the value of leather and is estimated to cost the leather industry £20 million per year.
Other effects such as weight loss, poor milk production and anaemia are less proven, even when there are large numbers of lice involved. This is probably because large numbers of lice are usually seen in animals that are under stress or under-fed or that have other current disease, which can all result in poor productivity without lice involvement
Types of lice.
There are four common species of lice in the UK, which can be divided into two different categories:
- Sucking lice
There are 3 species commonly found in the UK. These have relatively small narrow heads designed piercing the skin and sucking blood. In large numbers they can cause anaemia. They are usually found around the head and neck of cattle - Biting lice
Biting lice have larger rounder heads. They feed on skin debris, blood and scabs. Despite being apparently less invasive than sucking lice, it is biting lice that produce the most severe irritation. There is one species of biting louse found throughout the world. It is a reddish-brown louse about 2 mm long with a brown head. It is mostly found on the neck, shoulders, back and rump.
The life cycles of all species are similar. The female lays a few hundred eggs over the period of one month. These eggs are glued to the hair shafts, and hatch within a few days as nymphs (which resemble small soft adults). These develop, grow and moult three times before they become adult, with each stage lasting approximately one week. The entire life cycle takes between three and six weeks.
Diagnosis
On clinical signs and finding one of the three stages of the life cycle. Eggs are usually the easiest stage to spot, being found on hairs adjacent to bald, rubbed areas. Careful examination of nearby skin , with a magnifying glass, will usually detect nymphs and adults.
Treatment
Lice are spread only by direct contact between cattle. Adults, nymphs and eggs cannot survive more than a few days if removed from cattle. If properly applied treatment can eradicate lice from a farm.
Most insecticides are effective against adult lice and nymphs. However most are not very active against louse eggs. This means that after treatment, eggs can still hatch and continue the infestation, unless there is some residual action. Ask your vet for advice as to which product has the best persistence.
It can be important to know whether you have sucking or biting lice, because the different method of feeding means that they have different susceptibilities to treatments. This is particularly important if you are going to use an avermectin injection (such as ivermectin) as these are much more effective against sucking than biting lice. If you want to use such a product ensure you have the lice on your cattle identified.
The timing and frequency of treatments depend very much on individual circumstances. In many cases treatment in late autumn or early winter will give adequate control of cattle lice for the whole housing period. Whichever product you use, dose accurately, ensuring that you do not under-dose as under-dosing is the best way of ensuring the development of lice that are resistant to treatment.
Treat all cattle on the property at the same time if possible, choosing a time when they are not stressed or in poor condition. If groups have to be treated separately, such groups should be kept apart to ensure there is no contact between treated and untreated groups.
Is lice treatment necessary?
For cattle that have light to moderate numbers of lice, treatment cannot be justified in terms of improving growth rate, body condition or productivity. Treatment can improve hide quality, but as yet this is not of economic importance in the UK. However some quality assurance programmes in other countries (e.g. Australia) have made hide quality of economic importance and it is possible that this will come in the UK. Treatment may also become necessary on welfare grounds because of the easily appreciated discomfort that even moderate lice infestations cause.