Horse Disease Focus - Sweet Itch
An Itchy Problem
Your horse just came in from the field...and its rubbed its mane and tail raw. What caused this annoying problem? There are a number of things that can make a horse rub its mane and tail. Sometimes, too, pasture mates will chew a tail, even to the point of chewing it off, and there have been sad incidents of humans cutting off equine tails.
If it is spring through early summer, though, you could be dealing with seasonal recurrent dermatitis, also known as 'sweet itch'.
Often, the first an owner knows that a horse has sweet itch is that it has rubbed its mane and tail bald. This is caused by severe itching...it's just so bad that the horse scratches until the hair is gone and can even break the skin.
The horse may also swish its tail violently and roll far more frequently than would be considered normal. If turned out with other horses, it may solicit mutual grooming to an excessive degree...and some horses may even try to get scratches from the humans around. An affected horse might do crazy things to try and scratch. The horse may also show lethargy, agitation or lack of focus on work. Some horses develop head shaking.
The condition is most common in the spring and early summer, but can last through the fall with some horses. It is most common in southern Australia, where it may affect more than half of horses.
There is no cure for sweet itch. It is an allergic syndrome caused by the bites of certain midges.
Insect control is, therefore, the most important aspect of treating sweet itch. In some cases, the best thing to do is to bring the horse in and put it in a closed stable at dusk and dawn. However, this cure can cause problems of its own, such as triggering stable vices.
Only a DEET based insect repellent is known to be effective against midges. Draining any ponds on the property will also help. Most sweet itch 'ointments' contain an insecticide, specifically benzyl benzoate - these ointments should not be used if there is any broken skin, as they can then make the itching worse. Also, benzyl benzoate is toxic - it should not be used on children's ponies and as they recommend applying it with gloves, it might not be the safest thing for your horse.
A better solution might be to coat the horse with oil. Diluted bath oil works well, and there are sweet itch oils available. Always 'patch test' a new oil on a small area of the neck or flank, as some horses may be allergic to the oil.
Your vet may, in extreme cases, prescribe corticosteroids, but these should not be used on 'air fern' ponies or horses that have foundered in the past. Antihistamines are only somewhat effective in horses and can cause drowsiness - a problem if you intend to ride the horse.
Placing a fly sheet and neck cover on the horse to prevent midges from getting access to it is the very best and most proven solution. You can also apply a DEET based repellent to the fly sheet.
There is anecdotal evidence that feeding brewers yeast or (in England) marmite help some horses. Reducing the sugar in the diet might also be useful.
Some people have found that feeding garlic or oral fly repellents helps, whilst others have found the immune system boost associated with garlic actually makes the symptoms worse.
Cause and Prevention
Sweet itch is an allergy. As such it may be genetic, but it has been seen in all breeds and types of ponies, as well as in donkeys and mules. Most horses initially show symptoms between one and five years old. It is rare for a mature horse to suddenly develop sweet itch, but it might happen if a horse is moved from an area where midges are not common to one where they are, or if the horse is under extreme stress.
Sweet itch is not a contagious disease and it is quite normal for only one horse out of a large herd to show symptoms.
Preventing sweet itch is best done by controlling midge numbers. Horses grazed on water meadows are more likely to get sweet itch - if possible horses known to be susceptible should be moved to higher pasture. Drain standing water in horse pasture. This will reduce midges and mosquitos (which can carry worse things than sweet itch). Also get rid of rotting straw and hay and if you compost, keep the heap well away from your horses. Dispose of manure quickly.
Provide horses with a run-in shed, the darker the better - midges don't like to fly into dark places. Putting fans in the run-in shed is also helpful (and your horses will appreciate them in hot weather - a horse will find a fan in seconds if they're too hot. Trust me.)
Keep your horse, tack and rugs clean. Dirt and sweat attract insects.
Fly predators generally do not help if midges are the problem.