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Warmer weather means the onslaught of
flies, a condition which can reduce intakes and gains in
feedlot cattle. The
horn fly is a blood-feeder that feeds 20 to 30 times per
day. A population of several thousand horn flies may be
present on one animal. When large numbers of these flies are
on cattle, the cattle bunch and expend considerable effort
fighting the flies. They will often stand in water or seek
shade trying to get relief from the flies. When they do
this, they fail to eat normally, and thus gains are reduced.
Dealing
with flies in a timely manner using an appropriate contorl
method can help to reduce losses. Chemical control for
horn flies include insecticide-impregnated ear tags,
self-treatment dust bags and oilers, animal sprays, pour-ons
or spot-ons and feed additives. Because of their short
life cycle, horn flies quite easily become resistant to
control methods. However, there are ways to reduce the
chances of flies developing a resistance.
Horn
fly insecticide resistance management practices include:
-
Not tagging
cattle until horn flies are present.
-
Adding a
supplement treatment method in mid-August (dust bags,
oilers, sprays or pour-ons).
-
Not treating
animals in a weight gain mode (replacement heifers).
-
Removing the
tags in the fall after a frost.
-
Rotating the
insecticides in the tags yearly.
Place
dust bags and oilers where cattle are forced to use them to
obtain feed or water, or in loafing areas where they spend
considerable time. Since bulls and older cows tend to
dominate self-treatment devices, provide enough oilers and
dust bags to treat all of the cattle.
Although
sprays, pour-ons and spot-ons will control flies for short
periods, the stress to cattle in using these methods
probably offsets the benefits of the fly control. To keep
the horn fly population below the economic threshold would
require treatment at least every three weeks. However, the
following control methods can be used in mid-August to
supplement ear tags. If systemic insecticides are used, they
will provide grub control and reduce lice numbers as well.
Small
sprayers and dusters powered electrically from a vehicle
battery are available. If the cattle are not wild and are
treated often enough, these can provide good horn fly
control.
Feed
additives are insecticides that pass through the animal's
digestive system and destroy developing fly maggots in the
manure. While feed additives generally destroy 80 to 90
percent of the developing fly larvae, there may not be a
corresponding reduction of flies on the animal. Newly
emerged flies migrate to the closest cattle. An untreated
herd may provide enough flies to keep fly populations above
the economic threshold for both treated and untreated
cattle.
Boluses
that contain insecticides also are available. These are
retained in the cow's reticulum and slowly erode, releasing
insecticide into the digestive system. They do provide a
constant insecticide release which the feed additives may
not if some animals don't eat the feed or mineral containing
the insecticide. Fly migration also may render these
ineffective.
Issued in
furtherance of Cooperative Extension work, Acts of May 8 and
June 30, 1914, in cooperation with the U.S. Department of
Agriculture. Kenneth R. Bolen, Director of Cooperative
Extension, University of Nebraska, Institute of Agriculture
and Natural Resources
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