Bone broth won't hurt anything and I think they would enjoy it, but a more concentrated protein source would be more help. Canned sardines or tuna or even wet cat food are options, as is switching to a high protein feed.
I tried to buy a 10 lb bag at TSC yesterday. THey no longer have it in 10 lbs, only 50. And they were out. I'm not going to buy 50 lbs of something I use just a few weeks a year.I do like the idea of the calf manna!
So I'll get some sardines or something. Just have to make sure they aren't laced with salt.