3 August 2001

Photosensitive cattle face risk from sun

CATTLE suffer with sunburn just as humans do, but sunny weather can also bring on cases of photosensitisation, which occurs when digested substances react with skin pigments causing lesions, crusting and hair loss, experts warn.

Gareth Bell of the Royal (Dick) School of Vet Studies, Midlothian, says photosensitisation is common in summer and affects light coloured or non-pigmented areas of the skin, such as the eyes, nose or ear tips.

Primary photosensitivity is caused by eating plants containing photodynamic agents, such as ragwort, St Johns Wort and bog asphodel.

"Without careful management of pasture weeds, these agents can enter skin pigments and, when activated by ultraviolet light, skin reacts by becoming itchy and sore – like sunburn," says Mr Bell.

The disease is not contagious and may only affect a few grazing cattle in the herd, but lesions can become infected by flies, and cattle become uncomfortable causing growth rates to suffer.

The disease can also be caused by liver failure, adds Mr Bell. "Plants, such as ragwort, will damage the liver, so the animal is unable to efficiently remove toxins resulting from chlorophyll metabolism or produce proteins for growth." These cattle will show signs of liver damage – loss of appetite, weight loss and depression/stupor – as well as skin damage and are unlikely to fully recover.

Treatment of photsensitivity is simple, but the process of skin healing may be slow when the disease has been allowed to progress.

"Itching lesions will continue to spread on parts of the body exposed to light, so infected cattle must be kept out of sunlight and treated with anti-inflammatory and antibiotic drugs, when necessary."

Cattle usually feel more comfortable within four to five days and will generally recover. When skin has healed, cattle should be put out to graze in the evenings and gradually exposed to sunlight, adds Mr Bell. &#42