Summer Horse Health Problems - Part 2

This article is from the December 2019 Horse Deals magazine.

Photosensitisation

Photosensitisation is commonly confused with sunburn but is potentially much more serious. Primary photosensitisation occurs when a horse eats plants containing a compound that reacts to ultraviolet (UV) light from the sun. When these compounds circulate in the blood system near the surface of unpigmented skin it causes a chemical reaction which results in damage to these areas of skin. In secondary photosensitisation, the horse cannot break down the normal circulating levels of photodynamic compounds from plants, due to liver damage, this leads to the same reaction.

Photosensitisation results in painful blistering of the skin, followed by the formation of tight, crusty scabs. These will appear on the pink skin under white markings, such as on the face and legs. Over time the scabs will slough off.

Treatment: Start by protecting your horse from sunlight. If his entire body is affected, have him spend his days in a shady stable or yard. If the blistering is limited to his lower limbs you can use wraps to shield them from the light. A UV-blocking fly mask with a nose flap should be used if his face or muzzle are affected. The scabs are painful and should be left alone to slough off naturally. If the scabbing is extensive or your horse seems otherwise unwell, call your veterinarian, who may prescribe medications for the pain and inflammation.

Address the cause: Check your horses’ pasture for plants that cause photosensitivity, such as alsike clover, buckwheat, perennial ryegrass or St. John’s wort. Your veterinarian may also want to check your horse has normal liver function with a blood test.

Queensland Itch

Queensland itch (also called sweet itch) is an allergic reaction to proteins in the saliva of small biting midges (Culicoides spp.). The allergic reaction can occur anywhere on a horse’s body but is usually seen in the areas where the midges commonly bite; around the roots of the mane and the withers and around the tail head. The local reaction results in an intense itchiness, which can cause the horse to obsessively rub so much he damages the skin causing crusty, inflamed, hairless patches of skin on the affected areas. Certain breeds do seem to be more genetically susceptible, including British breeds of horse such as Welsh Ponies and Clydesdales.

Treatment: Treatment and prevention relies on shielding the horse as much as you can from the midges. A wide variety of fly-proof garments including masks and rugs are available which can help protect your horse. Fly sprays also help, but make sure they are repellents and not just insecticides, which only kill after the flies have already bitten. You can also adjust the turnout schedule to keep your horse indoors at dawn and dusk, when the midges are most actively feeding.

If management changes alone don’t seem to be helping your horse, make an appointment with your veterinarian to discuss other options. Medications such as corticosteroid shampoos, creams
and injections can help stop the inflammatory reaction and make your horse more comfortable.

Allergies

Common allergens of horses can be widely divided into three groups:
1. Skin allergens e.g. midge bites or shampoos.
2. Respiratory allergens to airborne particles e.g. dust and pollen.
3. Ingested allergens e.g. certain forage, foods and plants.

Allergic reactions can be anything from mild to life-threatening although thankfully anaphylactic reactions are extremely rare in horses. Weeds and grasses, along with insects, cause the most trouble for horses, so allergies are often seasonal, depending on which insects are active and what plants are blooming.

When your horse has an allergic reaction, his immune system perceives a threat from something relatively harmless and mounts a response against the “threat.” This reaction can instead damage the horse’s own body tissues. Additionally, he can become ‘hypersensitive’ to that specific allergen so the next time he’s exposed to it, the reaction is likely to be quicker and stronger. This reaction can look like excessive coughing and nasal discharge for respiratory allergens, or raised itchy areas of skin varying from a small localised reaction up to huge welts over the whole horse.

How to manage: Allergies are generally not curable, but they are manageable by keeping horses away from the allergen or protecting them from it. For example, protection from insect bites with barriers like rugs or fly repellent may help. Washing can be used to remove contact allergens from the skin, and a horse with a dust/mould allergy could be kept in a grassy paddock instead of a dusty stable.

If the reaction becomes very severe or itchy, then veterinary attention may be required to supply anti-inflammatory medications.

Conjunctivitis

Conjunctivitis is swelling of the membranes around a horse’s eye, caused by an infection. It occurs when trauma to those tissues opens the way for bacterial invasion. In summer windblown dust or flies can cause irritation causing the horse to rub his eyes, leading to bacterial invasion of the sensitive membranes around the eye, resulting in conjunctivitis. Unlike pinkeye in people and cattle, conjunctivitis in horses is not contagious.

A horse with conjunctivitis has swollen eyelids, often with angry-looking pink or red membranes protruding through the lids. There may also be a discharge from the eye, varying from clear and watery to a thicker yellow or white discharge. If you open the lids, you’ll see a normal, clear globe below. This is important to help distinguish conjunctivitis from other, much more serious ocular conditions such as uveitis, corneal ulcers or fungal infections. Likewise, a horse with conjunctivitis won’t be sensitive to light, whereas a horse with a more serious eye condition likely will be.

Prevention: The best prevention for conjunctivitis is a well-fitted fly mask. Not only will this keep insects away, but it will cut down on the dust that blows into your horse’s eyes.

Treatment: If your horse does develop conjunctivitis, the treatment is a topical antibiotic eye ointment, which your veterinarian can prescribe. A visit will likely be required to verify it is just a simple conjunctivitis and not something much more serious, as other eye conditions can deteriorate rapidly if not treated promptly.

Bruised hooves

Like your own skin, a hoof can bruise in response to trauma, causing blood vessels within the hoof capsule to rupture. You may even see bruises at the time of trimming on a newly pared hoof. In summer time, hoof bruises are most commonly caused by working the horse on hard, dry and stony ground or from repeated leg stamping in response to flies.

A horse with hoof bruising is likely to be “footsore” or lame, particularly on firm footings. Your horse may start taking shorter strides, or will be reluctant to walk on certain surfaces. If the hoof capsule cracks and bacteria enter, a bruise can turn into an abscess, and the horse will become dramatically lame. Fluctuations between wet and dry conditions in summer can further exacerbate these problems.

Prevention: Keep it slow on hard or stony ground. Hard, compacted ground isn’t just a problem for hooves, it can cause a multitude of lameness issues for horses as it causes concussive stress and strain on bones, joints and ligaments. If possible, ride on a specially prepared arena instead.

In addition, make sure he has adequate fly protection in the paddock to keep him comfortable. It may even be worth shortening his summer trimming/shoeing schedule to keep his hooves in top condition and minimise the chances of him losing a shoe, or feet becoming overgrown or cracked. If your horse is still having trouble with his hooves, you could explore some other options, such as pads, synthetic or glue-on shoes and other state-of-the-art products.

Treatment: Generally, treatment may involve the application of a poultice and administering pain relief. Rest your horse until the soreness resolves. This usually only takes a few days, though a deep bruise could affect the horse for longer.

Written by Dr. Rachel O’Higgins bvms mrcvs from Kilmore Equine Clinic

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