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Florida Fly Control for Cattle
July, 2018
Laura
Bennett, Multi-County Agent, UF/IFAS, Dade City
Controlling flies on livestock in Florida is a
challenge. Please note the
word, “control.” We would love
to substitute that word with “eradicate”, but that is not realistic.
Our main pests are horn flies and face flies.
In Florida, it seems as if we never really get a break from the
pests. There are a few options
that can give some relief to your cattle.
It may seem somewhat obvious the reasons to control
flies. However, if you consider
the reasons, it might prompt you to make an extra effort.
First, it is estimated that horn flies take 20-30 small blood meals
each day. The pain and
irritation the biting causes prevents adequate food consumption and rest.
This chain of events results in poorer milk production and lower
weaning weights. Second, biting
flies are carriers for diseases such as anaplasmosis. Third, horn flies can
cause severe damage to teats on heifers.
So, how many can we tolerate if we cannot eradicate?
The economic threshold on beef cattle is 200 flies per cow; above
that you are losing money.
What products are available?
Most sprays will only provide a moment of relief, so
it is desirable to find something more long-lasting.
Feed-through products use an insect growth regulator or a larvicide
to disrupt the life cycle of the fly in the cow manure.
The down-side is that your neighbor must use the product as well
because flies can travel. Fly
tags are another option. The
caveat is that the tags should be rotated based on product formulation and
should be removed after 3-5 months.
Letting the last little bit “trickle” out of the ear tag can set up
some insect resistance creating “super flies” that do not respond to any
product. Dust bags are highly
effective. However, you must
put them where cattle are forced to use them and it is not practical for
large cattle operations.
Photo Credit: J.F. Butler, UF/IFAS
Forced-use dust bags positioned correctly to ensure self-application by cattle when visiting the water trough.
W
hat about no treatment at all?
Perhaps solve the problem-not treat the symptoms.
It is estimated that the heritability of fly resistance in cattle is
very high at .58. The simplistic
view is to cull cows that have lots of flies and keep younger cows to slowly
turn the heard toward resistance.
The effectiveness of Brahman breeding in causing lower numbers of
insecticide-resistant horn flies has been documented.
Mean
horn fly numbers decreased significantly as the percentage Brahman breeding
increased with 50% Brahman breeding reducing horn fly numbers by 140 flies
per cow (Steelman, et. Al, 2003).
Brahman cattle have 3 times the number of hairs per unit of surface
area than do most British and Continental breeds.
Each hair follicle has two sebaceous glands that secrete a substance
that reflects sunlight and provides a natural resistance to insects. Cattle
with a very slick and shiny summer hair coat usually have less fly problems;
this could be a way to select for fly resistance as well.
If milk production and weaning weights are reduced by horn fly
presence, maybe breeding can prevent the losses.
Within-breed variation occurs as well.
Interestingly, as frame size increases, cattle still maintain the
same number of hairs in their coat.
When you enlarge frame size, you have more space between hairs and
less production by the sebaceous glands as they are also reduced per square
inch. Additionally, each animal
produces a natural chemical called thrombin which counteracts the fly’s
anti-coagulate factor. Flies
have more difficulty feeding on animals with higher levels of this compound
and won’t choose the animal for their host.
One last note: bulls
usually have two to four times as many flies as cows because flies are
attracted to testosterone. Bulls
have a hard life in more ways than one.
C. D. Steelman, R. W. McNew, R. B. Simpson, R. W. Rorie, J. M. Phillips, C.
F. Rosenkrans; Evaluation of Alternative Tactics for Management of
Insecticide-Resistant Horn Flies (Diptera: Muscidae),
Journal of Economic Entomology,
Volume 96, Issue 3, 1 June 2003, Pages 892–901,
https://doi.org/10.1093/jee/96.3.892
Progressive Cattlemen
https://www.progressivecattle.com/topics/reproduction/8324-when-it-comes-to-flies-producers-look-to-genetic-resistance
EDIS
http://edis.ifas.ufl.edu/in952