Nutritional value of whey

I made yogurt, and it was runny, so I drained it, and now I have a lot of whey. I know that it contains some of the protein from milk, but what about the other things in milk, like calcium or Vitamin A/D? Is whey nutritionally valuable, or just a waste-product?

ETA: I have Googled this, but I need some context for the answers I’m reading. How does whey compare to milk, or water, or eggs or whatever?

When I visited a cheese factory in Gruyere in Switzerland in 1997 they were saving the whey and, I believe, selling it to farmers as pig feed. I had visited the same factory in 1971 and things had changed quite a bit. In particular, they put the whey through a cream separator and, I assume, discarding what came out.

It is also possible to make whey cheese. You essentially boil it down to a cheesy residue. It’s not bad, but it takes a lot of power to make a small quantity of cheese. Norwegian geitost (goat cheese) is made from whey. When I make cheese, which I do regularly, I usually discard the whey, although in the summer I will pour it over the garden.