Like Humans, Farm Animals Vulnerable to Sunburn
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Farm animals share a common discomfort with man. They can become sunburned.
Although less common in the Midwest than in Sun Belt states, exposure to ultraviolet radiation may cause skin damage to dairy cows, light-colored beef cattle and sheep. With cows, damage can be so severe the animals lose patches of hair and skin, leaving underlying tissue scarred.
Dairy cows are among the most susceptible, said Timothy Johnson, a Purdue University Cooperative Extension Service dairy specialist.
"It would be the animals which are a majority white coat color for the Holstein breed, which is essentially a mix of black and white," Johnson said. "Look at the white patches of skin and you'll note that there's not just the white hair color, but the underlying skin also reflects those light-versus-dark patches."
Research indicates cows that feed in wheat pasture where certain weeds are present are more likely to develop sun sensitivity, or what is known as sun scalding, Johnson said. A chemical reaction occurs within a cow's body when the animal consumes wheat and such toxic weeds as foxtail barley, alsike clover, nettle, spurge and St. John's wort.
"The prevalence of chlorophyll in the rapidly growing wheat plant releases some toxic compounds which increase the sensitivity to the sun," Johnson said. The process is called photosensitization, he said.
Younger wheat plants contain more chlorophyll, which explains why sun scalding is a greater threat in April and May than in early summer, when wheat begins to head and turn yellow, Johnson said.
Johnson visited a Harrison County farm earlier this year where he saw sun-scalded cattle. About 15 percent of the farm's 300 dairy cows were sunburned. Johnson said he was able to pick chunks of hair and skin off some animals.
Like humans, sunburned cows feel pain. The stress reduces production potential, Johnson said.
"Anything that's causing cells to die on the animal is a cost, and takes away from the ability of those animals to produce," he said. "Think about how humans react to being severely sunburned. There's a great sloughing off of that skin and a loss of protein and energy. And there's also, in humans at least, the sun scald problem of cancer."
Johnson recommends farmers who choose to graze sun-sensitive cows in wheat pasture wait until later in the day and feed the animals other forages in the morning.
"The key is dilution, if wheat pasture is going to be part of their feeding program next year," he said. "Dilute the amount of wheat pasture that the animals will consume by offering some grass hay to those animals first thing in the morning. Realize that about 60 percent of the grazing activity and intake will go on between sunrise and 10 o'clock in the morning. This would be the time to restrain them from the wheat."
Sheep producers also should keep an eye out for sun scald. Photosensitization can develop if sheep eat weeds, although most of the ones that cause trouble aren't native to Indiana.
Sunburn can signal other problems in sheep, said Michel Levy, associate professor of large animal medicine in Purdue's School of Veterinary Medicine. "It could be liver disease or bacteria affecting the liver," he said.
Sheared sheep are no more vulnerable to skin damage than unclipped sheep. "The sun's rays can go right through the wool coat," Levy said. "It can lead to damage of the wool and loss of production."
For more information about toxic weeds and their affect on animals, read Purdue Extension publication WS-9, "Indiana Plants Poisonous to Livestock and Pets."
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