I always worry about our first calf heifers being too fat as we run on irrigated pasture. But as winter sets in and they start using some of that fat as energy, and then calve, they breed back okay and go on and do their job. Of course you don't want to run them too hard and then play catch up to get weight back on them.
I would agree that they can have some problems if they are too fat, but BCS 5 or 6 is where cattle should be at going into winter.
To me it really depends on the cow if she loses a calf and whether or not to keep her again. We tried that keeping open heifers last year because we had got quite a bit of money tied up in them. Guess what, they came up open again and hit the road. If a heifer loses her calf for no apparent reason, and acts like she would like it to be alive, I'll give her another chance.
We lost two calves this weekend, one was a first calver and she showed no sign of even caring if she had a calf or not. The calf wasn't cleaned up all the way and she was never concerned at all when I went to pick it up, she's gone.
We had a cow calving and the calf's legs were hung up in the pelvis. I got a rope on her and got her tied up to the circle to pull the calf. Got the legs coming first then didn't even have to pull it, the cow pushed it out. Calf was dead, untied the cow and she never even attempted to look at the calf and took off. She's gone.
I think you need to be real careful on heifers that you keep over if they lose a calf. If they don't learn how to raise that first calf, how will they be the next time??