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An ‘introduction’ to Sweet Itch by Will Marshall BVMS MRCVS


Bent Limbs in Foals


Sweet Itch or Summer Seasonal Recurrent Dermatitis (SSRD) is a seasonal hypersensitivity skin reaction caused by the saliva of the Culicoides midge. All types and breeds of horses can be affected by sweet Itch and it is reported that up to 5% of horses and ponies in the UK are affected by the condition. The majority of horses and ponies do not react to midge fly bites. However in animals with the condition,the hypersensitivity occurs when the midge bites, causing an overreaction by the animal’s own immune system to the allergen (in this case the midge saliva). We can think of it a little like a peanut allergy in some people! This overreaction causes an inflammatory response in the


by Susan Donaldson BVMS MRCVS


Foals can either be born with bent limbs or these may develop over the first few months of life, often being caused by other developmental problems. In this article, we will look at the significance of these bent limbs, what kinds of deformities occur and how these can be treated.


Why are bent limbs a problem? Any deviation from a straight leg can alter the foal's foot placement and therefore lead to uneven pressure being placed on the joints. Once the foal has stopped growing, any bend in the limb will be permanent and the uneven strain on joints can influence future soundness for athletic performance.


Bent limbs can be divided into angular deformities and flexural deformities.


Flexural deformities are identified by assessing the foal's limbs from the side. The most common of these is 'contracted tendons' where the


tendons which run down the back of the limb are too tight meaning the limb cannot be


straightened. Forelimbs are most commonly affected. If the foal is able to move and feed from the mare, then mild cases often simply require careful


monitoring and no specific treatment. In severe cases, treatment includes intravenous injections of


oxytetracycline; which is an antibiotic but has the useful side effect of relaxing tendons and ligaments; and


bandaging and splinting of the limbs to attempt to straighten the leg, allowing the foal to move around and the tendons stretch. In older foals, tendons


may become contracted after a period of rapid


skin which includes the release of large amounts of histamine from the skin cells. This in turn leads to pruritis or itchiness, which causes the horse or pony to rub and scratch to relieve the sensation.


Clinical signs and symptoms of Sweet Itch The midges tend to bite certain areas of the animal, most commonly attacking the base of the mane and/or tail head area. The withers, hips and forehead are also common sites to be affected. In some horses/ ponies, the midline of the abdomen in front of the sheath or udder can also be affected, sometimes without any mane or tail involvement. It should be noted that the symptoms


and lesions can completely disappear and heal over the winter months.


Sweet Itch symptoms in the areas highlighted above include;


SEVERE itching Foal with severe flexural deformity of forelimbs. Photo by Luanne Hunt.


Hair loss or thinning (alopecia) Skin thickening becoming folded and corrugated and turning dark in colour. Flaky dandruff Exudative dermatitis ie. Weeping/open sores often with a yellow crust of dried serum - if sores are not attended to properly a secondary infection (pyoderma) results


to stretch and by use of anti-


inflammatory drugs. If the tendons do not relax, the foal's foot will begin to take on a 'boxy' or 'club foot' appearance. In such cases, surgical intervention may be indicated. Where surgery is performed, normally the accessory ligament of the deep digital flexor tendon (ALDDFT) or 'inferior check ligament'


Affected horses and ponies may swish their tails vigorously,


joint, most commonly the knee (carpus), but the fetlock, hock or even a


roll frequently and attempt to scratch on anything within reach. They may pace endlessly and seek excessive mutual grooming from field companions. Even when kept behind electric fencing with nothing to rub on, they may scratch out their mane with their hind feet and bite vigorously at their own tail, flanks and heels. We may even see them drag themselves along the ground to scratch their belly or sit like a dog and propel themselves round to scratch the top of their tail. There can be a marked change in temperament resulting in lethargy with frequent yawning and a general lack of spark, or they can become agitated, impatient and lack


combination of joints can be affected. We can also describe the direction the leg is deviated in: deviation to the outside (laterally) is described as valgus, whilst deviation to the inside (medially) is described as varus.


which attaches the deep We can divide ALD into problems which digital flexor tendon to the back of the knee is cut.


The other kind of flexural deformity which is seen in young foals is laxity of the tendons. Hindlimbs and specifically hind fetlocks are most


commonly affected, with foals often being


described as being 'down' on their fetlocks. In general, affected foals require little or no


treatment, unless the deformity is so severe that the heels and


fetlocks make contact with the ground and therefore require


protection by bandaging. Glue-on shoes can also be used.


Carpal Valgus. Photo by Luanne Hunt.


growth and initially these foals can be treated by restricting their exercise, trimming of the heels to help the tendons


Angular limb deformities (ALD) can be defined as a deviation of the leg


from a straight line when the limb is looked at from the front or back. The


the foal is born with and those which occur during growth, usually in the first six months of life. Those noticed at birth or soon after are perinatal deformities and those developing during growth are acquired deformities. It is very common for foals to be born with a mild carpal valgus where both forelegs are slightly deviated to the outside from the knee and a slight toed-out conformation; as these foals grow and their chests widen these problems often self-correct. In premature foals, the small bones in the knee and hock may not have calcified properly and therefore are softer meaning that they can be 'crushed' when the foal is moving, leading to bent legs and in time, if untreated, arthritis in the affected joints. These bones are best assessed by x-rays. If the foal is only mildly affected, bandaging or splinting and box rest can be used while the bones become more calcified.


Acquired ALD is likely to have a number of contributing factors, including injury, overfeeding or nutritional imbalances, and inflammation of the growth plate in the cannon (physitis).


So how can ALD be treated? deviation can be centred over one specific X-rays of a bent leg will allow the


Scratching an itchy mane has left this horse with a scurfy skin and obvious hair damage


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