Can someone explain to me how an animal that lives off grasslands can be allergic to the one food that makes them thrive?
Whether or not you need something to survive will have no effect on an over-enthusiastic immune response.
My sister-in-law has a cat that's allergic to fish. Maybe its something in the hay, like ragweed?? Or is a mold growing in it? So what is the horse fed now?
My soon to be sister in law is allergic to something in water. She has to boil everything and can't eat foods that have a lot water in them. So I guess sometimes life just sucks.
Hay - meaning alfalfa, I presume - is not a natural horse food. Horses are set up to eat mostly grass. You can get grass hay - bales of timothy or the like. If the horse is sensitive to dust, or mold, that's a different problem. Again,it's an artifact of modern animal husbandry
your horse is only eating the green hay, right? Its in the middle on the bale, not the exposed outside.
Basically what's happening is that the horse's immune system is a little mutated, and exposure to hay, for some reason, is causing it's immune system to turn on and trigger an acute inflammatory response. If it's really the hay that's doing it. It could be an allergen in the hay. The immune system is composed of highly variable genes, and under very strong evolutionary pressure to change from generation to generation. This means that there are often problems with immune systems, since not all genetic combinations are good combinations. In fact, most mammals recognize family based on smells that are related to the MHC-major histocompatibility complex. The more similar MHCs, the more you consider someone related. Most mammals also seem to prefer mates with MHCs that differ from their own by a moderate amount. This is likely due to selection to find a mate with a different suite of MHC genes to increase the number of immunities the offspring has, while retaining the immunities the parents likely have to pathogens present in the current environment.
