We've had Tarentaise for going on 20+ years, and we also have Red and Black Angus. I'll be straight up with what my experiences have been.
-Purebred cows make excellent mothers, very protective, good milk. However, we've found a few bloodlines have, for lack of a better word, dumb calves. The ones who can't figure out how to suck and seem overall slow, which usually it only lasts a few days, but its a pain during that time. We've tried to get rid of those lines. We have also had problems with big calves (100+ lbs), and we try very hard to stay away from that when we AI and select our herd bulls. But talking with some other Tar breeders, 90 lb calves aren't that uncommon. The cows can have the big calves though with no problems. This is why all our Tar heifers get bred to calving ease Red Angus bulls, just to be safe. Even with our selective breeding and culling, we seem to have some problems still. We have also had problems with teats, even though we have been culling hard against it. The teats seem to balloon out, making it hard for the calves to suck. Again, this is usually found in certain bloodlines. We've culled so hard for these problem traits that we've gone from 70 head of Tars down to 38 head.
-Bulls are aggressive breeders. We've never had a problem with a yearling not testing well on his BSE. They cover the cows well. In our operation, we AI the cows before they go to summer pasture, and the bull covers whoever doesn't stick. So one Tar bull is with ~40 hd and everybody gets bred by the time the bull is pulled.
-When we wean calves, we have found the Purebred Tars end up weighing 100 lbs less than the Angus, Red Angus, and crossbreds. Same with yearling weights, the Tars always seem to be a bit lighter. However, crossbred Tars are the heaviest on those weights. Our heaviest yearling weight on our heifers (they have no corn, just hay and grass) was 1000 lbs, and she was out of a Tar cow and Angus bull.
-If you are thinking of exhibiting Tars for any reason, I will caution you on that. I've had judges ask me what breed they were. They are not made for the show ring, no matter how good. (at least in my area)
-Where I'm at, we have a hard time selling purebreds to go onto other purebred herds. The demand here is in the Tar crosses. We have a huge demand for Angus x Tar heifers. Most of the purebred females we sell end up getting bred to black bulls, and most of the purebred bulls we sell end up going on crossbred cows (of any breed mix).
On your question about having 2 purebred herds, it can be done. Like I said, we have 3 purebred herds and it works well for us. You just have to keep good records and have enough pasture to do it.
Just my :2cents: .