Thanks for this explanation. When my dairy farmer in law grew alfalfa, it was the greenest, richest stuff I had every seen, grown on fertilized ground, with so little stem the flakes would barely hold together.
Perfect for lactating dairy cars for maximum production of premium milk.
My horses would have foundered if they had even been next to the stuff.
ETA: My other vague recollection is that the protein was too high for horses, and would likely cause epiphysitis and OCD, and also, the calcium/phosphorus ration was wrong for horses. We were a fun crowd around the dinner table, the dairy farmers and me.