Originally Posted by Corporal
Yes, hay loses nutrition over the course of about a year after curing, but it loses no more nutrition after that. After one year your alfalfa hay will be lower in protein but better for your horse.
This is not exactly how it works! Oxidation, water, radiation, etc. degrade hay. The more exposed to the elements hay is the faster it degrades. The more "stored under ideal conditions" it is, the slower it degrades. Hay in the center of a stack in ideal conditions will be great for many years. The top 1" of a stack will go downhill quickly. If you can find some common sense, it is very easy to understand.