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Pink eye and Fly Control



     Pink eye, medically called Infectious Keratoconjunctivitis, is an eye infection that affects cattle, sheep and goats.  Each species of animal has their own separate type of bacteria that cause the infection; i.e. the cattle type does not affect sheep, etc.  Pink eye in sheep and goats is usually caused by Chlamydia.  This information will discuss the pink eye in cattle.

     The first sign of a problem is an increased tearing in the eyes, pain and swollen eyelid tissues.  Later a white spot develops on the cornea, which is a sign that the cornea has an ulcer developing.  An ulcer is a hole developing in the cornea.  Corneal ulcers appear like a bubble of jelly on the eye; which is thick fluid inside the anterior eye chamber starting to come out through the small hole.  If not treated, the ulcer can cause permanent damage to the eye.

     Pink eye is caused by bacteria called Moraxella bovis.  A couple of other diseases, such as Infectious Bovine Rhinotracheitis and Mycoplasma, can also cause eye ulcers and eye infections in cattle.  Cheat grass seeds in the eye, fly larvae or eye worms also can cause similar types of eye irritation.  It is interesting to note that we usually see pink eye in the later summer.  With the long days the bright sunlight bothers some cattle??especially if they have white faces, such as Herefords.  If the grass is tall then the grass brushes and irritates the eye.  Eye irritations predispose the eye to pink eye infection.  The Moraxella bacteria are carried from one eye to another by flies.  The flies are attracted to the eye because it is tearing.  Usually younger cattle are affected as older cows can develop a type of immunity to this type of eye infection.

     The treatment of pink eye depends upon the severity of the infection and if an ulcer is present.  Injecting the eyelid with a antibiotic and a drug to help decrease the irritation may be indicated.  Spraying the eye with an antibiotic solution or powder, an injection of a antibiotic in the muscle, and spraying the face for flies also helps.  Sometimes we need to treat the patient more than once.  If the eye is severely affected suturing the eyelid closed may also be required.  We recommend closely monitoring the other cattle nearby, spraying their faces for flies, and/or applying an antibiotic to their eyes periodically to help prevent their eyes from being affected.  There is a vaccine available to help prevent pink eye.  Fly control and the vaccine are methods to help prevent the disease.  Pasture management and the breed of cattle also can be considered for some producers.  We recommend the vaccine if the outbreak is early in the season, or if pink eye seems to reoccur every year.  Any vaccine takes 1?2 weeks to work, and thus late in the fall we may not advise this vaccine.  Unfortunately there is nothing that we can easily give in their feed or water that will effectively treat the cattle.  Conjunctivitis can be caused by many other organisms; herpes/IBR and malignant catarrhal fever (cattle), mycoplasma (all species), chlamydiophyllia (cattle, sheep, goats, camelids), plus many other species of bacteria which we may need to culture.

     It is very important to monitor the progress of the animal with the treatment advised for pink eye.  Please call if the problem seems to worsen.  It may take 2?3 days before the animal treated for the first time seems to improve.  The white spot, or corneal scar, may take weeks before it goes away.  In severe cases, the scar can be permanent.


The Staff at the Nelson Road Veterinary Clinic



Livestock, fly control



     We all dislike flies, as they bother us when we are working.  To have an excess of flies there is a reason, such as wet manure, livestock themselves or wet soils around.  The method of insect treatment depends upon the fly species that you want to control.  There are various methods of control.  No matter what method you use you will not be 100% successful.

     Fly wasp parasites are sold to prevent problems.  These wasps do work, but studies show that the flies parasitized are usually the common housefly (Musca domestica).  This is because the wasp easiest to be raised is the Muscidifurax zaraptor, which prefers the housefly.  Houseflies rarely bother animals, as they do not bite.  As with any parasite, rarely is the host totally destroyed by the fly wasp parasite; expect a 35% efficacy with Muscidifurax.   The stable fly (Stomoxys) also causes problems in livestock, and both flies look similar.  The face fly normally points its head downward and is found in wetter areas than the housefly.  Another fly wasp, Spalangia nigroaenea does attack the stable flies; but this wasp is very difficult to raise and is rarely sold as a fly wasp.  The stable flies usually are a problem in the spring and early summer, and naturally their population fades away as the summer gets hot.  House flies and stable flies are the most common flies around a cattle feedlot and moist manure areas.

     There are insecticidal products to feed to livestock to reduce the fly population; these are called fly blocks and fly licks.  Fly control boluses also are available for cattle with developed rumens (over 450# weight).  These products only work with flies that lay their eggs in fresh feces less than 24 hours old.  The housefly does not lay its eggs in fresh feces.  The horn fly (Haematobia) and the face fly (Musca autumnalis) lay their eggs only in fresh stools and can be controlled by these oral products.  The horn fly is about 1/2 the size of the face fly.  The horn fly bites the host while the face fly does not actively bite.  The face fly “sponges” up its meal, especially from the facial tears and can easily spread the cattle pink eye disease (Moraxella bovis).  If a biting fly has bitten an animal, then the face fly licks and irritates the wound to keep it open.  Only the female face flies feeds on animals; the males feed on flowers.  Face flies can also carry eye worms (Thelazia) in horses and lower chest dermatitis (Stephanofilaria parasite) in cattle.  Raybon & Equitrol, both are tetachlovinphos, and are such a product used as “a feed through insecticide”, and in horses this organophosphate product can sometimes be toxic.  We do not recommend the organophosphate products for pregnant mares and young foals.  Feed through products and IGR’s do not control or repel mosquitoes, gnats or horse flies; they do help control the other flies. 

     There are also insect growth regulator products (IGR) which one can feed to horses for fly control, including the house fly.  IGR’s keep the insect larvae from developing into adults; s-methoprene is such an example.  These products are also called fly growth regulators (FGR).  Diflubenzuron is such an examples; BT or bacillus thuringiensis is also such an example, yet not used orally in livestock.   If used as a premise spray or fogger the IGR compound needs to come into contact with the egg or immature larvae.

     The topical insecticides and sprays help somewhat.  A quality product lasts longer.  There are some sprays that supposedly last up to 14+ days, yet we do not actually know of a good product that lasts more than 7-10 days.  The spot-ons and the pour-ons last the longest.  The alcohol and water based spray products have the quickest kill, yet the oil based products last the longest.  Some oil products can remove the hair if used improperly; we recommend the spot-ons and pour-ons be placed on the back of livestock near dark to help avoid this rare problem due to intense sun and heat.  In horses the pour-ons do not work as well for gnats biting the legs, and thus a long acting spray is indicated every few days if there is a problem below.  The back rubbers and oilers work fairly well with cattle, if placed in the right locations.  Fly control in a barn can be greatly helped with the automatic aerosol application systems.  The pyrethrin compounds are good, safe products that we recommend for the average spray control program.  Foggers can be used on large premises with severe fly and mosquito problems.  Foggers are fairly inexpensive to purchase for the small landowner; we recommend the hand held propane foggers.  There are also carbon dioxide and heat producing units which attract the biting female mosquitoes and gnats.  These “mosquito magnets” can help reduce the breeding population of these biting insects.

     The biting flies, such as gnats & midges (Culicoides) or black flies (Simulium), deer flies (Chrysops) and horse flies (Tabanus) breed in wet, marshy areas.  To control these flies you must work to remove their breeding grounds.  The stable fly (Stomoxys) normally bites the horse during daytime.  The stable fly can carry a parasite that causes “summer sores”.  Culicoides (sand flies, gnats or midges) can cause irritation from bites to the ears and chest area.  Culicoides breed in standing water and like to feed in the morning or near dusk.  Horn flies (Haemotobia) causes an irritation near the horse’s belly, with the area usually being more localized that Culicoides.  Fly ointments and spot-ons can adequately help fly problems in horses.  The gnats that affect the ears of horses and dogs are best prevented by use of the spot-ons or ointments.  DEET (N, N-Diethyl-meta-toluamide) is not to be used in animals because of its possible toxicity.  Spot-ons are the most concentrated form of the pour-on products.  Most pour-ons are a concentrated form of fly sprays, which are formulated to last longer.  Spot-on and pour-on products are systemically acting, insecticides that you pour onto the animal’s back.  The pyrethrin and permectin products are safe to use in our opinion.  These products will help control-biting insects by killing the fly after it has bitten the animal and/or been exposed to the insecticide.  The best method to reduce the biting insect population is to use the systemic pour-ons which last a couple of weeks.  Pour-ons do not repel flies completely, and for some biting fly problems we may recommend a pour-on and also a repellent spray.  With aural flies (gnats) and for mosquitoes (encephalitis prevention) we recommend both types of products and/or the spot-on product.  Horses should not routinely have the pour-on or spot-on products applied to the back area below the saddle, especially during the middle of the day, as hair loss may occur.  We recommend that a pour-on be applied in the evening to horses.  For cattle we may recommend ear tags as the first choice of biting fly control; ear tags area not approved for use in other species such as horses.  It should be noted that to use one of the systemic spot or pour-ons on a patient not on the product’s label, such as dogs or especially cats, a severe reaction can occur. 

     Bot flies, also called grubs, lay their eggs on an animal where the larvae hatches and migrates through the body.  Each species is different on where the final stage of the larvae ends up at.  Horse bots (Gastropholus) are in the stomach, sheep (Oestrus) are nasal bots, and the cattle grubs (Hypoderma) erupt from the animal’s back.  Cuterebrae and other bot flies affect rabbits, domestic animals and wildlife.  All of these are treated with avermectins or other systemic fly products.  Since the life cycle of these flies is mostly within the animal, the periodic fall/winter systemic treatment(s) is the method to help prevent an increase in the bot fly population.

     Blowflies are pigmented in the bright colors of black, blue, green or bronze.  These flies like a high protein diet, such as a dead animal, spilled milk or wet feed.  Fly strike in sick animals can be caused by these and other fly species.

     There are other ways to control flies besides sprays and pour-ons.  The oilers and dust bags help control flies for cattle on pasture.  Ear tags work well to help control face flies and horn flies in cattle.  These tags need to be changed yearly to a different product to reduce the problem with insecticide resistance.  Alternate pyrethrin tags with organophosphate products, but not both on the same animal.   Two tags per head should be applied; these ear tags should be applied when needed and removed after the fly season.  Sticky fly ribbons help a little.  The head strips your can hang on halters and the face nets provide relief for some horses.  Any time the horn fly count is over 125 flies per animal, fly control is indicated.  The economic threshold for the face fly count is 5 per animal.  When purchasing the baited jugs, the model where the fly enters from the bottom works better than the top lid type jars.  When the baited fly jugs catch more than 250 flies in a week, or if the spot cards catch more than 100 flies, we advise a more aggressive fly control program be started.  If more than 10 stable flies are found per animal, their breeding habitat should be sought in addition to fly control.  Always count 10% or 10 animals to determine if additional fly control methods are indicated.  Fly control baits also help with the houseflies, yet these are toxic to animals and thus we do not recommend them routinely. 

     Besides the biological and chemical control, one of the most important fly control mechanisms is cleaning up the manure and reducing the wet areas.  When these fly breeding areas are found a method to prevent the problem should be considered.  A natural vegetable oil can be sprayed on the standing water if you are unable to drain it.  Some species of cattle, such as Bos indicus, also have a natural resistance to flies.  These Indian cattle are also more susceptible to toxicities from insecticides.  Always read the label for the species of animal, the dosage and drug withdrawal times.  Some insecticide products labeled for horses, cattle or dogs will kill the more sensitive species such as cats, birds, exotic animals and Bos indicus crossbreeds of cattle.      

     There are flies that do not harm livestock.  The Dump fly (Ophyra) feeds on organic matter and even other fly larvae.  These flies are shiny black and smaller than the house fly.

     The other parasites such as lice, ticks, straw itch mites and mange are treated with different methods, as directed by the veterinarian.  Some systemic insecticides for lice, such as the avermectins, will not kill the biting flies after a few days.  If one does have fly resistance problems to organophosphates or pyrethrins, a mid summer deworming of an avermectin product may help.   Always read the label; some products for grubs should not be used on cattle between June and November.  Avermectins may deworm the patient and kill lice and mange but they will not help in long-term fly control if they are the only product used.  Fly control programs should be evaluated periodically for their need and/or changes in products for a more effective program.




When Is It Economical To Spend Money Controlling Flies

in Cattle?


     Controlling flies is similar to spraying weeds; at a certain minimum level it is economical to take the time and effort to control these problems.

     House flies can carry diseases, and in general make it uncomfortable for animals and humans.

     In dairy cattle anywhere from 5 to 60% of a milk production drop can be due to biting flies.  A horn fly population of 500 flies can draw 1/2# of blood a day from an animal.  It is recommended to treat for horn flies when there are 200 or more per animal.  In a feedlot situation where seasonally flies are a problem, the feeding of an insect growth regulator (IGR) can be started 30 days before the fly season until 30 days after the first frost to reduce horn fly problems.  There are also IGR products for horses if it is the horn flies causing a problem. 

     Lice suck blood and/or chew their host animal.  When there are more than 3 lice per square inch of livestock, it is recommended to treat.

     Biting stable flies can cause an annual loss of $9.80/cow if there are 5 flies on one leg (1995).  If a cow is shaking off flies at 20 motions per minute, this will cause a loss of production and feed efficiency.  It is recommended to treat for stable flies when there are 5 or more flies per front leg.

     Face flies can transmit pink eye.

     Besides loss of production flies can carry diseases.  Biting flies transmits Anaplasmosis, bluetongue and other diseases.  Studies have been shown mastitis bacteria can survive for more than 2 weeks with carrier flies.