Dane12,
you can take a core sample of the hay and have it tested (just as many people have their soil tested). The test, at least in my area, is very cheap, and it lets you know EXACTLY what your hay has, so you can develop a correct strategy for feeding in the winter (supplements etc.) Usually gives you a protein level and a TDN level. The protein level is important, but if the TDN is low, it's all for nothing, and can actually induce the cow to eat less.