Most horses on good pasture can store enough vitamin A in their livers to carry them through the winter months. Hay on the other hand loses 10% of it's vitamin A for every month after it's cut. Copper is another neccessary element needed for curing rain rot.
Vitamin A does have a toxicity level. Beta Carrotine does not.
I recently got a rescue foal that had a nasty case of rain rot all over his poor little body, even on his nose! His skin was a mess, covered in that blasted gunk, fur falling out, dull, flakey and just plain hideous.
We've had him for a couple of weeks now and his rot spots are clearing up from the inside out! No picking or scrubbing, not even topical stuff was needed. He simply got better from the inside out.
Here's what I've been feeding him:
8/10 cups cut up carrots = carrotine
1/2 cup soy beans = protein
1/2 cup yogurt = probiotic
1/4 cup flax seed = omega 3s
1/2 flake alfalfa = calcium & protein
Electrolites in his water
He is on average quality hay and no grains or other suppliments. His goopy eyes have cleared up, his fur is getting shining and no longer falling out and the rot scabies are just brushing away. Now when you part his fur you see good skin and good looking fur down at the roots.
It is a lot of carrots but you aren't going to OD him on them, it's naturally taken into his system and every nutrient is utilized. Plus, he thinks it's Christmas everytime he gets fed. LOL
I buy the 25lb bulk bag carrots for juicing which runs me about $8.
Soybeans at the local grocery, they are toasted and in the bulk bin section.
Flax seed is also in the same bulk bin section. Both around a buck a pound.
He gets the carrots with each feeding and the other stuff at breakfast. He's a happy clam.
And so am I!