Fly Control

Fly control is an essential part of summer horse management.

Flies can be the vectors or carriers of many conditions in horses or may contribute to reactions that can have serious implications for horses. Such conditions include:-

  1. Thought to be transmitted by biting flies that transfer the sarcoid cells from one horse to another or to different parts of the same horse.
  2. Flies can irritate the eyes causing excessive tear production and tear staining down the face. Sometimes this can become worse leading to eye irritation and in severe cases, eye ulceration.
  3. Sweet-itch. An allergic reaction to midge bites (Culicoides species usually) that causes intense itching on the mane and tail areas in particular. There is an allergic reaction to the bite that causes itchiness and leads to self-trauma that causes the skin lesions typical of sweet-itch. There is evidence that this is an hereditary problem. This commonly starts between 2-4 years of age and can cause devastating damage due to the self-trauma.
  4. Habronemiasis (summer sores). These are small but hard lumps containing a granular material which is often calcified. They occur because of flies depositing larvae on the skin which then burrow in and cause a reaction.
  5. [African Horse Sickness.(AHS)] This is a viral disease transmitted by midges (Culicoides species). Although AHS has never occurred in the UK, the midges are present and an outbreak could occur if the virus was to gain access to the UK. This could have severe consequences to the UK horse population because of the high mortality rate (90%+). A live vaccine is available in Africa but there is none available in the UK. However, there is a great deal of research being carried out at the moment in developing new vaccines.
  6. [West Nile Virus.] This has not occurred in the UK although can be transmitted to humans, horses or birds by mosquitoes. It causes nervous system signs in a small percentage (10%) of horses although up to 50% of these will die. There is a vaccine in the USA but no vaccine available in the UK.
  7. [Equine Infectious Anaemia.] (Swamp Fever). This is a notifiable disease in horses and is caused by a retrovirus. It occurs when biting flies transfer blood from one horse to another. Horses may be infected for many years with very vague signs such as lethargy and anaemia.

Management and fly control

  1. It can be as simple as turning horses in the field overnight when the flies are less active rather than during the day. For sweet-itch the times of peak fly activity/feeding are dawn and dusk.
  2. Commonly fly control is a combination of rugs and fly-masks. The most usual are the full body rugs that protect the belly area and neck along with the fly masks that can often be attached to the rug.
  3. Fly repellents. Usually permethrin liquids such as Deosect that are diluted to 2% and used topically either by spraying or wiping daily.
  4. Avoid areas where there is standing water and/or woodland where flies commonly breed.
  5. Barrier creams or oils. Grease or oils on the skin can help prevent midges biting.
  6. Fly screens on stable doors help to prevent midges gaining access to the horses when stabled.
  7. Wind speeds in excess of 5mph (8kph) prevent midges from flying.


  1. (Nicotinamide). This is a form of vitamin B3 that is available without prescription but is most effective before the condition begins to cause clinical signs. It is a powder that is mixed with water and fed daily. There is also a topical cream for “spot” treatment. Cavalesse helps to reduce the histamine release that causes the intense itching as well as increasing fat in the skin. Simon Constable’s Equine Vets were involved in the development of the product as one of the first ten practices in the country to be involved in the evaluation and use of this product.
  2. Anti-histamines. These are a safe medication for horses (they do not have the same risk of laminitis as with steroid use) but have limited effectiveness. Piriton is one of the most commonly used anti-histamine.
  3. These are a very effective drug when used topically or in tablet form. However, there is a risk of laminitis especially with prolonged use (as is normally required in the treatment of sweet-itch or fly bite reactions). The treatment is normally started with an injection and then as an oral powder for longer term therapy. Dose regimes vary; a higher dose may be given initially to get the itching under control before reducing to a lower level. Alternatively lower doses may be attempted to control the clinical signs; this is commonly carried out with ponies or horses at risk of laminitis.
  4. Desensitisation injections. These are effectively a “vaccine” against the allergens (the things that cause the allergy) and although they sometimes have a good effect, they do not work in every case. Commonly a blood sample is taken to evaluate the presence of antibodies against different allergens (common ones include midge saliva, tree pollen, moulds, plants/grass types etc). A desensitisation injection can then be developed for the individual horse that is given as a long-term course of injections. These injections are given sub-cutaneously and are very well tolerated.
  5. B Vitamin supplements or alternatives such as brewer’s yeast may have a good effect on reducing itchiness.


Although not controlled in the same way as flies, care must be taken against ticks in areas where there are sheep grazing with horses. They can bite and “latch on” to a horse especially in the leg or abdominal area.

As well as being an irritation, some species, Ixodes can also transmit a spirochaete infection called Lyme Disease (Borrelia burgdorferi) which can cause quite devastating problems such as fever, arthritis, heart problems and behavioural changes.

It can be easily treated by antibiotics but the diagnosis of Lyme Disease can be difficult because of the general and non-specific clinical signs unless previous exposure to this tick is known.