Q: I would like information on frostbite and sunburn during the winter months. I have a 7 year old black and white paint. He's had trouble with a sore nose which started in the fall. I've never had this problem with him before.
A: First have a veterinarian examine the horse (if you have not already). It is unlikely that frostbite and sunburn are the underlying issues for the sore nose. Frostbite on healthy, adult horses is rare. If frostbite is a problem, it's usually seen on the ears. Sunburn can be a problem as sunlight can reflect off of snow and cause a sun burn. However, this is much more common in higher altitudes.
A potential cause of the sore nose is photosensitization resulting from some type of liver damage or ingestion of poisonous plants. Examine your horse's hay and look for wild parsnip, a weed that commonly causes photosensitization and retains its toxic effect when dried in hay. In the fall, a certain mold (Cymodothea trifolii) that grows on legumes (alfalfa and clovers) can also cause photosensitization, which might help explain why you observed symptoms in the fall. The mold literally causes black blotches to occur on the underside of the clover leaves.
Treatments will depend on the cause of the photosensitization. Working with your veterinarian to diagnose and treat this problem is recommended.
More information on photosensitivity
By J. Wilson, DVM, C. Ward, DVM, and K. Martinson, PhD, University of Minnesota