I have several nurse cows. Mostly jerseys, and jer x hol cows but a couple of guernsey crosses also. Right now I have 2 jersey 1st calf heifers that have a total of 6 calves on them. One will let anything nurse, the other isn't too happy about it but will tolerate and the more aggressive older calf will stick with her. The one who will take any calved about a month ahead of the other one. They get approx 10-15 lbs grain each a day. I purposely want them to raise at least 3 each and the one that is great with the calves, I may pull off the 2 biggest ones and put a couple more on her.
I try to get beef x dairy calves to put on them. Many farmers here are now breeding their top cows to dairy semen and the rest to beef so there are more beef x calves available.
Since you are feeding some grain as well as pasture, which is what I do, the cow ought to do fine. The calves will grow good and if they learn to eat some grain too, then weaning will be easier. Mine all learn to get in the bunk and eat grain right along with the cows. I will have 4 more calving in sept and oct and they will all get at least 1 or 2 more calves each. One is an old cow that only can raise 2 and one only has 2 quarters and will raise 2. The other 2 usually will get a total of 3 calves each and one of them will take anything so often will get a second set of calves at about 4-5 months. All depends on when she gets bred back. I try to breed at least 1 breeding AI, sometimes twice, then use an angus as a cleanup bull.
Any calf on a cow is going to do better than on milk replacer if she has a fair amount of milk and the calf can learn to eat some grain too. On the holstein, he won't get that pot belly that they often get after coming off milk replacer at about 10-12 weeks , and getting just hay and grain. They look much more filled out and healthy coming off the cow.