Photosensitivity
is a serious thing. It’s not just superficial. Preventing the
scratches and stuff on the face (or other pink areas of skin) is not solving
the problem. Here’s an excerpt from a Cattle magazine (one can find
many articles related to horses as well, but this one explains it most clearly
and succinctly):
“Springtime brings the warming sun and lush plant growth, but it can
also bring danger to some grazing animals. The culprits are certain plants that
result in a skin disease called photosensitization.
Eating these plants makes some grazing animals more sensitive to the sun.
The penetration of light into the sensitized skin causes cell death, swelling
and itching. Patches of skin may even slough off.
The damage is due to sensitization of unpigmented skin, which is unprotected
from ultraviolet rays, according to Stan Casteel, a veterinary toxicologist at
the University of Missouri.
The cause of this reaction, says Salmon, ID, veterinarian Robert Cope, is
usually plants that create liver damage.
"When the liver malfunctions, toxins build up instead of being filtered
out and some get in the blood," says Cope. When these toxins get in the
blood they cause photosensitization when they reach the skin, he adds.
Iowa State University toxicologist Tom Carson agrees. In an animal with a
damaged liver, normal body metabolism may cause photosensitization because
by-products of plant digestion accumulate in the skin instead of being cleared
through the liver, he says.”
