Generally Calf Manna is used as a supplement to a grain. I have not heard of anyone who has just fed straight calf manna along with hay, so I will not comment wether you can or can't because I have no idea!
Calf-Manna (from what I know) is a very rich feed (lots of protein). Therefore, you should lower the amount of feed you give them. Example; say you feed a 16% (protein) grain and you feed 1 lb of it (just an example). Then when you switch to Calf Manna (I don't know exact protein level, but I think it is higher than 16%) you want to feed a lower amount so that the goat gets about the same amount of protein. So if Calf Manna is 32% protein you should only feed a maximum of 1/2 lb of feed.
An overload of protein will surely upset their stomachs.
I don't know the numbers either but yes it is very rich. I put a lot of weight on my horse with a small amount of calfmanna. If your goats are like mine I don't think they would eat just that mix. I usually have to mix a small amount of both into their grain to get them to eat it.....and my goats are not heavyly grained. But I often say mine are freaks
Yes, I agree with what has been said. Calf Manna is not designed to be fed straight. It is very high in protein at 25%. We feed about 1/3 of a pound of calf manna a day with two other grains mixed in.
BOSS also should not be fed straight either as it can upset the stomach too. BOSS is very oily and if too much is fed it can coat the stomach and intestines and cause any nutrition to not come through. We feed only about a handful of that each a day mixed in with two other different grains.