Common pasture plants and some medications can make cattle more sensitive to sunlight, resulting in skin ulcers and tissue death, said Jeremy Powell, veterinarian and associate professor for the University of Arkansas System Division of Agriculture.
“Photosensitivity is more than just sunburn. Some veterinarians describe like an allergic reaction to the sun,” Powell said. “Photosensitivity may also be an indicator of something deeper — liver damage.”
In some cases, the photosensitization can come from otherwise benign crops such as certain species of clover or alfalfa. Even that pasture stalwart, bermudagrass, has come under suspicion, though the specific agent that causes the photosensitivity isn’t yet known.
Phil Sims, Pope County extension staff chair for the University of Arkansas System Division of Agriculture, said he received a call from a local producer telling him the skin was falling off the legs of his cows. A local veterinarian had diagnosed the symptoms as photosensitization.
“Seeing the skin fall off your cattle isn’t a common occurrence, and your first thought is ‘what are we dealing with?’” Sims said.
He said, “all kinds of disasters run through your mind and you get this sick feeling in your stomach until you can figure out what is really happening.
“Our specialist and related research of the topic seem to support what the veterinarian was seeing,” Sims said.
If the liver is damaged or diseased, it’s ability to breakdown plant pigments such as chlorophyll. The pigments build up in the liver and eventually enter the bloodstream. When they reach the skin, exposure to ultraviolet rays results in skin damage.
Damage to the liver could come from parasites, infections or eating poisonous plants or moldy hay. Coal tar-derived treatments, tetracycline and some sulfonamides have been suspected of inducing photosensitivity.
Photosensitive cattle should be kept in the shade and the sunburned areas should be treated to halt any potential infections and steroids can help heal the skin.
Contact your veterinarian if you suspect your livestock are suffering from photosensitivity.