Summer ailments

Heat stroke is equivalent to severe hyperthermia, causing the internal organs to disfunction, and which can be fatal. A heat stroke is caused by intense work or by transport during very hot weather, especially when heat is accompanied by humidity. Therefore it is essential to make sure the horse is able to drink regularly and in sufficient quantity. A shelter, whether natural or artificial, can protect the horse from very hot conditions. Working the horse or transporting him should be undertaken at the coolest times of the day.

Pink-skinned horses are more sensitive to UV radiation, particularly on smooth-skinned areas (with little or no hair), for example around the eyes and muzzle. These depigmented areas absorb the UV rays more than pigmented areas. In summer they can get sunburnt, which shows as characteristically red skin and skin sensitivity, which can also peel.

These reactions can be more serious if the skin is photosensitive. In these cases swelling and scabs are often observed. These are due to an accumulation of photosensitising agents in the skin, either through ingesting them or through direct contact between the skin and certain plants or medicines (e.g white clover, tetracycline). Plants containing pyrrolizidine alkaloids, such as ragwort are the cause of liver disorders and also cause photosensitivity.

Repeated exposure to UV radiation for pink-skinnned horses can promote skin tumors, especially around the eyes.

To avoid the horses getting sunburn several options are available :

• Use masks which cover the muzzle and the ears, or even use combo anti-UV fly sheets.
• Keep the horses stabled when the sun-rays are most intense (between 12:00 and 3:00pm).
• Apply sun cream to the depigmented and smooth-skinned areas. This needs to be repeated at frequent intervals, as the horse will remove the layer of cream when grazing moist grass or when drinking. Zinc oxide is more water-resistant, but it is not advised to use around the eyes.

Summer is also a period which is favorable for plant-poisoning, as fewer food resources are available in the fields, and these plants are more resisitant to dry conditions. This is when horses can eat plants that they would normally avoid. Two poisonous plants are particularly an issue :

• Ragwort poisoning the cause of digestive and nervous system disorders
• Catsear (Hypochaeris radicata) poisoning, which provokes locomotor disorders : Australian srtinghalt

When the resources in grass lessen it is essential to give the horses access to hay.

These insects can cause skin irritation and itching, even hypersensitivity, which in turn can cause serious pruritus. Sweet itch or seasonal recurrent dermatitis (SSRD), usually starts from spring and goes through to autumn, but the clinical signs  (broken mane and tail hairs, wounds, thickening of the skin along the neck and tail area) are most marked in summer due to the presence in large numbers of midges, responsible for this hypersensitivity, in the environment.

By mechanically irritating the eyes, or through carrying pathogens (bacteria, viruses, parasites), flies can cause conjunctivitis. The horse will show signs of closed eyelids, weepy red and swollen eyes.

Flies can also transfer parasitic habronema larvae to the conjunctival tissue, or to minor wounds. The larvae will then exacerbate the formation of proud flesh around the wound which does not heal over. These skin complaints disappear in the winter but reappear in the spring. These wounds are known as cutaneous habronemiasis, or summer sores. They are seldom seen in France, but are potentially more frequent in the South.

Flies are also the cause of skin myiasis. They lay eggs around wounds, the larvae hatch and feed on secretions and dead organic tissue thereby taking part in cleaning the wound. Unfortunately some species also feed on healthy tissue, worsening the damage and possibly causing secondary infection. Additionally they are a source of significant bother for the horses.

Some flies also transmit infectious diseases, particularly two diseases which fall under state regulations :

• Equine infectious anemia, which is spread between horses by biting flies, especially horse flies.
• West Nile fever, which is spread to horses by culex mosquito bites, the mosquitoes who are themselves contaminated by infected birds.

A dusty environment can also exacerbate clinical repiratory symptoms in horses affected by equine asthma.

Prevention can be established by decreasing these horses’ exposure to dust with for example some of the following measures :

• Watering the arenas and work areas
• Keeping the grassiest paddocks for affected horses
• Regularly moving around the drinking and feeding areas which are subject to trampling.