Summer time is hopefully a period that we are blessed with good weather and sunshine and while this is inevitably good for the soul, the sunshine and resulting UV, sadly can have negative implications for our equine patients namely in the form of sunburn and photosensitization.
The first, simple sunburn, occurs when light- coloured skin, including flesh marks, becomes red and scaly following excessive exposure to UV light. Similar to humans, the severity of the damage depends on the strength of the radiation and the individual’s skin sensitivity. Light-coloured skin is predisposed due to a lack of melanin pigment which absorbs UV light and scatters the radiation. Hairless skin is also more severely affected. The most common affected area is arguably the muzzle.
Mild cases generally self-resolve provided further exposure to UV light is prevented and the skin is given a chance to heal. More severely affected patients require veterinary attention and topical medications are frequently indicated (usually steroid-based creams).
Prevention is based on avoiding exposure to intense sunlight by stabling at periods of intensity, use of water-repellent sunblock and if the muzzle is an ‘at risk’ area, use of a face shade mask (which includes a shade to cover the muzzle area).
· Whilst intact, ragwort is generally quite unpalatable and horses don’t tend to eat it unless no alternate forage is available. Ragwort becomes much more palatable for horses when it is treated using a herbicide but hasn’t yet fully decomposed or when it is cut down and subsequently dries out. Therefore, one of the main sources of exposure to our horses is when it is inadvertently incorporated into hay or haylage.
· The toxin in ragwort, pyrrolizidine alkaloid, is generally a cumulative toxin. While a toxic dose may be consumed on one occasion, it is much more common for a patient to consume the toxic dose over a longer period of time i.e. years.
· The toxin causes irreparable damage to the patient’s liver which can lead to liver failure which is fatal. Clinical signs of liver failure are often only apparent when greater than 75% of a patient’s liver is affected. Clinical signs include depression/abnormal demeanor, reduced appetite, weight loss, jaundice, diarrhoea and photosensitisation to name but a few.
· Diagnosis is based on the presence of compatible clinical signs, with/without a history of grazing ragwort-infested pasture, blood work and ideally, a liver biopsy.
· Treatment is generally of a palliative nature.