by Dr.Kelley Neuhold, Loomix Technical Service Specialist

I am a 4th generation SE Colorado rancher, at the age of twelve I took the money I had saved and purchased two bred cows. Those two baldy cows were the start of my current cow herd. From that time forward my dad and I have run cows together and one of the common conversations we have each year is should we feed fly control. Two of our common concerns are does feed thru fly control work and is it cost effective.

We make a common mistake many producers make, which is starting to feed fly control too late. Dad and I don’t start thinking about fly control until we see flies which is about 30 to 60 days too late. Oral fly control should start being fed 30 days before the last hard freeze. In the continental U.S. start dates range from March 1st in the south to May 15th in the north. If a fly population is established prior to feeding fly control it will take 35 days to see a reduction in fly numbers. A pour-on, spray, or rub could be used in those situations to help decrease the adult fly population.
In my experience many producers mistake fly control for fly eradication, thus their disappointment with their control program. Fly eradication is nearly impossible to accomplish and never cost effective. Two hundred flies per animal is the economic threshold, if the fly population exceeds this threshold production and/or economic losses will occur. Table 1 demonstrates this point very well. Campbell (1976) evaluated the effect of fly control (treated cows 15 flies per cow vs untreated cows 469 flies per cow) on steer weaning weights in the sand hills of Nebraska. Under the conditions of this study fly control increase weaning weights 13 lb at $1.60 per pound that would mean an extra $20.80 per steer weaned. They did not report body condition scores of the cows but I would assume similar if not better body condition for the treated cows.

A three year study conducted in Louisiana evaluated the effect of fly control on replacement heifer performance (Table 2). Pregnancy rates were not different between the two groups, however replacement heifers treated for horn flies gained 15 pound more than heifers not treated over the 140 day feeding period. The greatest gains were realized in heifers that remained open. Open heifers treated for flies gained 0.25 lb/hd/d more than open heifers that were not treated for flies. This makes treated heifers 35 lb heavier over 140 feeding period, at $1.37 per pound, those heifers are $48 more valuable at sale time. This helps offset some of the cost associated with developing an open heifer.

Horn flies are the most economically relevant fly to the cattle industry, this is especially true for pasture cattle. Confinement operations may need to control other types of flies as well as horn flies. Face flies can also have an impact on your bottom line through the spread of disease such as pink eye. Houston (2010) estimated that pinkeye cost producers $150 million annually. Make sure the product you use is labeled for the fly or flies that are on your cattle. One benefit of oral fly control is that there is no need to rotate products, once you find one that works for you, you can stay with it.

To have a successful fly season remember these three keys. First start thinking about fly control before you have flies, don’t be like my dad and I. Second remember it is fly control, some flies are acceptable. Realist fly control reduces the population by 75 to 80%. And finally keeping fly population below 200 flies per animal can add pounds to your cattle and dollars to your bottom line.

Table 1. Effect of treating beef cows
for horn flies on steer weaning weights.¹

¹Adapted from Campbell 1976.

²Means with in a row with different superscripts differ
(P < 0.05).

Table 2. Effect of horn fly treatment
on replacement heifer performance.¹

Campbell, J. B. 1976. Effect of Horn Fly Control on Cows as Expressed by Increased Weaning Weights of Calves. Journal of Economic Entomology. 69:711-712(2).
DeRouen, S. M., L. D. Foil, A. J. MacKay, D. E. Franke, D. W. Sanson, and W. E. Wyatt. 2003. Effect of horn fly (Haematobia irritans) control on growth and reproduction of beef heifer. Journal of Economic Entomology. 96:1612-1616.
Huston, C. 2010.Pinkeye in Cattle. (Publication 2608) Extension Service of Mississippi State University.