There's a place near me that has some goats with cows. I see them graze together. Maybe the goats are feed their grain in the morning before they are let out and again in the evening when brought back to their pen. My cows are grass and hay fed.
Sheep can't have iron and there's something else too that is found in the grain and minerals for cattle. If you could pen them separate for graining you would be okay but, make sure the sheep don't get the grain for the cattle-you would almost have to be able to lock the pen for the cattle so you know the sheep can't get any. Personnally, I would keep them separate and not risk the chance.
I have 2 cows, 3 sheep, and 3 1/2 goats (one 3 month old) running together on the same acreage. Goat feed has too much copper for sheep, so now I just feed a 12% ( general)grain mix if I want to give them a treat and I have a mixed species pasture mineral, free choice that everyone can have. It's sooooo much easier than having separate rations for everyone. The cows just get grass (they're Dexters), and the sheep get 99% grass. The goats graze and browse the woods at the edge of the pasture. So far so good! karla
p.s. I'm going to run my hens behind them to break up the fly cycle, and next year I'll rotate them through the pasture to help break up the parasite cycles.