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Summer skin allergies in horses

by
01 April 2009, at 12:00am

John Baird discusses sweet itch and tries a new treatment.

Skin allergies, such as sweet itch, can be the bane of many horse owners’ lives; however, veterinary surgeons are rarely consulted on this serious condition which is often difficult to treat. Affecting three to five per cent(1) of all horses in the UK, sweet itch, or Summer Seasonal Recurrent Dermatitis, is caused by an allergy to the saliva in the bite of Culicoides midges. 

Sweet itch is particularly prevalent during the summer months, when midges are at their most active. All breeds and types of horses, ponies and donkeys are susceptible to the condition, although some breeds are more so than others. It is thought that the condition is hereditary and stress is also thought to be a trigger. 

The disease is not contagious, however if a premises is particularly susceptible to midges then more than one horse may develop the condition. 

Clinical signs

 Midges usually attack the dorsal surface (mane, withers, back, rump and dock) of the horse and clinical signs often develop in these areas. They include severe pruritus and hair loss, commonly in the tail and mane. The skin can become bald, inflamed, crusty and sore and as the condition progresses it thickens, becomes wrinkled and the hair becomes sparse and coarse with flaky dandruff. 

Exudative dermatitis may develop which can lead to secondary bacterial infection. These lesions are often found along the spine at the mane, forelock or tail and, in more severe cases, they spread down the body to the abdomen, saddle area, sides of the head, sheath and legs. 

The itching can become so severe that the horse scratches itself on anything in reach. Excessive mutual grooming from field companions is common and a horse may also shake its head or become restless if flying insects are close by. In addition, a horse’s temperament can change: it can either become lethargic or agitated and impatient, with a lack of concentration when ridden. 

During the winter, the skin may totally recover. However the disease often returns in the spring at the first contact with flies. It is, therefore, essential for owners to be aware of the potential risk of purchasing a horse during winter when there are little or no signs. If a horse has a mane and tail that look suspicious, it is advisable to inspect it closely for signs of hair loss which may suggest sweet itch. 

Prevention and control 

Sweet itch is notoriously difficult to manage and once a horse develops the condition it recurs every summer, proving a management nightmare for its owner. 

Prevention and control should include a three-pronged approach: decreasing the horse’s exposure to the midges, killing the flies and stopping the itching. 

Decrease exposure

 As midges thrive in marshy fields it is advisable, although not always practical, to relocate a horse susceptible to sweet itch to insect-free areas such as exposed, windy fields or chalk-based grassland. Grazing should be well drained and away from rotting vegetation, such as muck heaps, which may attract flies, and water troughs should be cleaned regularly to prevent flies from breeding there. 

The most effective protection for horses out at grass are light rugs and hoods which can cover all the areas of the horse susceptible to bites. Stabling horses at night from dusk to dawn, when flies are at their most active, and insect-proofing stables with fine-mesh screens will also help prevent horses being bitten. 

Ceiling or wall-mounted fans in stables create a breeze which prevents flies from landing on the horse. Stabling more seriously affected horses may do them more harm than good as scratching on a stable wall or door can cause a lot of damage. 

Insect repellents

 Insect repellents and insecticides may help control the midges and prevent them from biting the horse. Insecticides containing pyrethrins or pyrethroids can be effective. Benzyl benzoate will also keep flies away, but it has to be constantly reapplied. 

Insect repellents should be applied well before signs develop and should not be administered to inflamed or broken skin. All insect repellents and insecticides should be applied with care. 

Stopping the itching 

If a horse is bitten, corticosteroids may bring temporary relief by depressing the immune system but there are serious side effects such as laminitis. Antihistamines are effective, but high doses are required and they tend to cause drowsiness. Soothing lotions will relieve the itching and reduce inflammation but they will not deter further midge attacks. 

Maintaining a healthy skin

 A new range of easy-to-administer skincare products, Cavalesse and Cavalesse Topical (Janssen Animal Health), has recently been launched to help maintain and support a healthy skin in horses prone to summer skin allergies. 

Cavalesse is a natural food supplement containing a specialised formulation of water-soluble vitamins and minerals, including nicotinamide. Once a month the contents of each sachet are simply dissolved in water to form an oral solution, which can be administered daily via a special pipette, either by sprinkling over a small handful of feed or adding to a treat such as a sugar lump. 

The supplement helps horses maintain a healthy skin by reducing histamine release within the skin, moderating the excessive immune response, reducing antiinflammatory reactions and suppressing antigen induced transformation. 

Cavalesse Topical is a skincare gel that can be used in combination with the Cavalesse solution. The gel can be applied to the skin to help support natural defences from the outside, whilst the oral solution works in partnership from the inside. All preventive measures, such as utilising the insect repellents and administering the multi-vitamin food supplement, should be instigated in March and April before the midge season starts to prevent the midges from biting and stimulate a horse’s immunity. 

It is, therefore, important to encourage owners whose horses suffer from sweet itch to take action now to help protect their horses from this devastating condition. 

1. McCaig, J. (1975) Recent thoughts on sweet itch. Veterinary Annual, 15th edition. Edited by C.S.C. Grunsell and F.W.G. Hill, Wright and Sons, Bristol: 204-206.