I recently came across this 2-part Ohio State University video program on understanding hay tests and feeding hay to beef cattle. I posted it below in a response but thouoght it was worth putting up here for others that might be interested.

In the later parts it comes down to cow needs and seeing if your hay meets the cow's or heifers needs at certain points in their yearly cycle and weather. Discusses when to supplement and amount to supplement.

The program really points out the importance of energy/TDN vs protein. Seems like we are always talking about protein. While that may be critical for dairy herds, for beef cattle this program focuses on energy needs.

There is also a link to a very good picture chart on BCS.

I find this to be the best information clearly explained on a non-phd level about hay, understanding hay tests and beef cow/heifer feeding in the winter I have seen.

Ohio State University Hay Program - Part 1

Ohio State University Hay Program - Part 2

Ohio State University BCS Chart

Jim at Dawn