Do you have a sheep that has developed bald patches on their belly or sides during the summer months? Or patches of thickened bare skin they itch and itch and itch, often until they produce raw bleeding spots? Despite having these odd itchy spots, you can find absolutely no obvious reason for the irritation. Did it magically go away as if it was never there when the weather cooled down in the fall? If so, you may have encountered a sheep that has allergic dermatitis to the bites of Culicoides species insects. This condition is exactly the same problem as the condition better known in horses as sweet itch, or Culicoides hypersensitivity.
In horses sweet itch shows up mostly on their tail and mane areas making the condition extremely obvious. In contrast, in sheep the condition is most commonly seen on the bottoms of their bellies. Because of this it may go unnoticed unless it is an extremely severe case where the bald patches reach other portions of the body.
So what are Culicoides?
Culicoides are a teeny, tiny biting flies. You might know them by different names such as no-see-ums or biting midges. They are those tiny biting insects that have no qualms about flying through your window screens to bite you. If you have ever been bitten by one, then you know they produce an intensely itchy bite.
Culicoides are mostly active around dawn and dusk. They arrive in the spring and stay through the fall only disappearing once it starts frosting. Culicoides reproduce in wet areas, such as the marshes our farm is surrounded by. So unfortunately for us, they are a very big ongoing problem. Not only can they cause allergic reactions in our animals, but they are also vectors of the disease blue tongue which they can carry from white tail deer to our livestock.
Because they are so small and numerous, Culicoides can be very difficult to control.
They are almost never out on sunny days and might bite your animal without you even having realized it. The allergic reaction they cause may even be invisible for quite a while. You might not notice until the animals have itched holes in their coats.
This allergic reaction caused by Culicoides starts a viscous cycle. It causes the animals to itch, so they scratch themselves. This causes skin damage, inflammation, and irritation leading to yet more scratching. Additionally, it creates bald patches or raw areas of skin that are prime targets for additional bites from both Culicoides, and various other biting flies and insects. Left unchecked, the animals can itch literal holes into themselves leaving large raw bleeding patches. These open wounds are good candidates for developing infections, or fly strike. Fly strike is where flies lay eggs in a wound and you end up with a wound full of maggots.
Preventing and managing sweet itch
It is important to get Culicoides hypersensitivity reactions under control before it gets out of hand. If you have an animal showing early signs of Culicoides hypersensitivity, take action to break the cycle if at all possible. Try to do damage control before the animal is covered in huge bare patches of skin. If you have an animal that has had problems with this in the past, take a proactive approach. Try to prevent the problem before it starts. If they had a horrible reaction to Culicoides last year, most likely it will occur again this year.
Because this is an allergic reaction to the bite of the Culicoides insect, treatment and prevention requires protecting the animal from getting Culicoides bites. Unfortunately, this can be very difficult to do completely. Nonetheless, you should do your best to minimize the animals exposure. Even if you cannot prevent every single bite, less bites still equates to a less severe allergic reaction.
How do I limit exposure?
If possible, the best prevention is to bring your animals inside a barn before the Culicoides become active near dusk. Then turn the sheep back outside once the sun has risen in the morning. Additionally, because Culicoides are so tiny and difficult to exclude, having a large fan blowing over the animals in your barn can make a huge difference. This will keep the insects from being able to bite your sheep.
If you cannot practically bring them inside, then select night time pastures carefully. Pasture your animals overnight in areas that are as far away from moist areas as possible. It is also a good idea to try to choose pastures that are in open windy areas. Because Culicoides are so tiny, a breeze can help to keep them off of your animals.
Use physical barriers and insecticides on problem prone animals
You should use physical barriers or insecticides to deter Culicoides from landing on sheep that you know are sensitive to Culicoides bites. Petroleum jelly can be a good physical barrier for bare skin. We have also found that the horse ointment ‘Swat’ works well to keep biting insects off patches of bare skin. Keep in mind that any sort of physical barrier or insecticide repellent must be applied frequently for it to be effective. This is particularly true if your animals are rubbing off the barrier by itching the affected areas of skin.
If you have an animal that develops an open sore from itching despite your efforts to prevent this from occurring, you will likely need to bandage the affected area or use some other method to prevent them from being able to reach to itch the spot so that the skin can heal.
Lastly, you may need to consider culling affected animals if easily controlling the Culicoides hypersensitivity is not practical. Livestock are supposed to be working for you. Most sheep do not develop Culicoides hypersensitivity, so it can be a good idea to get rid of ones that do. Additionally, just like with most things, there is likely a genetic component, and this is something that you can select against. You should not keep replacement animals out of affected sires or dams.
We hope this will help you to spot and manage this frustrating condition if you are ever unlucky enough to come across it!
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