only if the hay is coming from teh same supplier fields right next to each other can vary greatly upon type of hay, if they have been fertilized or not, how they were seeded, how often and when they were baled
the best those of us who don't nto have a set hay supplier or our own fields can do is feed to the averages of that type of hay and pray honestly ...
Look into a ration balancer made for your area they are made to the averages IOW don't go with a BIG name company that distrutes nationally
look at the smaller companies like Seminole, Kent, Pennifield, Hall feeds you get my point ... more regional companies
I have been called the NSC Nazi more then once ... I hate traditional feed methods of loading our horses up on grains and junk food :)