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Fly control and oppressing pinkeye
 
Beef Herd Health
By W. MARK HILTON, DVM 
 
 Two nemeses of beef producers and their veterinarians are flies and pinkeye. Although pinkeye can occur at any time of the year, summer is still the most common time that we see outbreaks.
Control of face and horn flies takes a multifaceted approach and timing of each step is critical in success.
The use of insect growth regulators (IGR) or larvicides in the mineral starting one month prior to fly exposure is a well-proven management practice to reduce fly pressure. Use a product labeled for controlling face flies (all control horn flies), as they can spread the pinkeye causing bacteria from animal to animal. Check with your feed supplier on options.
Utilizing insecticide impregnated tags in cows and calves is a cost-effective way to help control flies. While putting tags in both cows and calves is ideal, using them in cows is the key. Also, don’t forget the bulls. They need fly control too. Rotate between pyrethroid, organophosphate and avermectin tags. There are many options on the market, and some are proven to be superior to others. Check with your herd health veterinarian to see what they recommend. If they have questions, I am happy to discuss the latest research. Also, be sure to wear disposable latex gloves when applying fly tags.
The top two concerns I see with use of fly tags is putting them in too early and then not removing them in the fall. Look at the map above and add 30-45 days to the time when you start the IGR. This is the ideal time to use fly tags. We want about 200 horn flies/cow when we apply the tags.
Remove the tags in the fall when cows are pregnancy checked. The tags are emitting a very small amount of insecticide now and that can breed resistance. Also, when you remove them, put them in a bucket that is on the pickup tailgate. If the farm dog chews on a few (not that it has ever happened to me), they can ingest enough insecticide to become ill.
I recommend using a pour-on product that is labeled for flies at the same time as I put in the fly tags. This gives a quick knock down of the fly population just as it is exploding. Do not use a macrocyclic lactone product (ivermectins, avermectins, etc.) if you are only targeting fly control. These products are also effective for internal parasite (worms) control and using them frequently for fly control allows the worms to become resistant to these products. We have not had a new class of dewormers come onto the market for about 40 years, so we need to preserve the products we have by not overusing them.
Many of the free choice mineral feeders come with an option that applies insecticide to the face of the cow as she consumes the mineral. These can be quite effective if they are kept recharged with insecticide.
If cows must walk through a narrow opening, using an insecticide soaked “fly wipe” can be helpful. There are also non-insecticide options where cattle walk through a “fly trap” where flies are mechanically “wiped” from the animal and then fall into a trap.
Spraying cows during the summer can be another effective way to reduce the fly pressure.
Herds that practice management-intensive grazing and never allow grass to become mature have less pinkeye issues than herds that allow grass to grow tall and form a seedhead. The grass can irritate the eyes and the seeds can lodge in the conjunctiva and scratch the eye. Keep grass under 10 inches by grazing or clipping to decrease the chance of irritation.
There are several vaccines for pinkeye on the market and they contain various strains of bacteria. Select a product with advice from your herd health veterinarian, as they are the best source of information for the ideal vaccine for your area. If you are still getting cases after performing all the above, ask your herd health veterinarian about culturing the eyes to see what organisms are responsible.
We will never eliminate flies from our cattle businesses, but we need to have a plan to control them. University of Nebraska research showed a 12-20 pound weaning weight advantage for calves nursing cows where fly control was practiced. Make a plan now with your feed supplier and herd health veterinarian so your cows will have minimal impact due to flies this spring and summer.
4/2/2024