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Detection
Control
With fall approaching, now is an excellent time to
consider treating your cattle for lice.
Cattle lice may be the most underestimated livestock
insect in terms of economic losses. The USDA estimates that
U.S. livestock producers lose $125 million a year to cattle
lice.
Heavy louse populations cause lowered milk production,
loss of flesh, stunted growth, general unthriftiness and
anemia. During severe winters, louse-infested animals are more
susceptible to respiratory diseases. Heavily
infested cattle are generally in poor physical condition
with rough, patchy hair coats that have a dirty appearance.
University of Nebraska studies and studies of others
indicate that moderate to heavy lice populations may reduce
weight gains of calves by as much as 0.21 lb/day. These
studies also indicate that calves fed at a higher nutrition
level had lower lice populations and were affected less
severely by lice than calves fed a maintenance ration.
Detection
Lice-infected
cattle may be detected because they exhibit excessive
scratching and grooming. Itching is indicated when barb wire
fences have hair on the barbs and the infested cattle show
hair loss and an unthrifty appearance.
Cattle with white faces and necks may show a dark, greasy
appearance if lice populations are heavy. Cattle can be
examined for lice by containing them in a squeeze chute and
examining the face, dewlap, neck, back and tailhead. Lice
can be seen by making a two-handed hair part of those areas
in good light. Lice numbers averaging more than three per
square inch indicate a need for treatment.
Control
Fall
applications of the systemic pour-on, spot-on, spray,
injectable or dip insecticides for grub control give added
benefits of reducing louse populations.
These treatments may not be enough to prevent a build-up
during severe winters. Most can be used again after the grub
treatment cutoff date (Nov. 1 to Feb. 1), and are quite
effective. Some may have a reduced treatment rate for lice
control.
Dursban (chlorpyrifos) pour-on is a non-systemic so it
can be used anytime, but the label has many use restrictions
concerning breed and sex of cattle. The Ivomec injectable
wormer is very effective for the blood-feeding lice species,
but may not control the chewing louse. Consequently, the
chewing louse may increase within a herd. Recently a pour-on
formulation has become available that should improve control
of the chewing louse.
Systemic insecticides used between Nov. 1 and Feb. 1
might bring about a host-parasite reaction as a result of
killing grubs while they are in the esophagus or spinal
canal of the animal. However, cattle can be treated
effectively with non-systemic insecticides if they need
treatment during the cutoff period for grub treatment.
Examine
treated cattle after about 14 days, regardless of treatment
method, to determine if a second or continued treatment is
necessary. Most insecticides are not effective against eggs,
so lice hatched after treatment may reinfest the animal.
When spraying or dipping in the winter, pick a warm day so
the cattle will be dry by sundown. This practice reduces
cold stress.
Insecticide dust bags and oilers used for fly control
also can be used for control of lice. The best results are
obtained when these self-treatment devices are used to
prevent a serious build-up of louse populations. Once heavy
populations are present, it will take two to four weeks to
reduce the louse population to non-economic levels.
Insecticide-impregnated ear tags used for fly control have
not been effective in controlling lice.
Source:
John B. Campbell, Extension Entomologist, University of
Nebraska, Cooperative Extension
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