I'm innocent....I didn't say he was thin....
Alfalfa flakes can vary a lot!! I have them between 4 and 9 lbs, even sometimes within a bale flakes vary, but not that much.
Grass hay is even more of a difference.
I got me a little fish scale and randomly weigh the flakes, or my filled nets.
It would be a good idea, tho, to get a basic idea of what his calorie intake is, and if it's only as reference for later.
The vit/min or RB is helpful. Too much missing in hay nowadays.