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. Lice in Cattle The NADIS data show that last winter there was an
increase in the number of cases of lice seen by NADIS 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: 1) 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 2) 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.
Bovicola bovis: The biting louse (from
http://www.bris.ac.uk/Depts/VetSci/ah/fas.html) 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. Richard Laven PhD BVetMed MRCVS
Copyright © NADIS 2003 |
