It really is to your advantage to keep good records..... how else will you remember (from last year or the year before) who weaned off a nice calf or had a dink one? In this economy, you need every extra dime and I'd rather have cows that raise good calves. When I had six cows it was easy to keep up with.... not any more. Only half of them are named and the other half I go by their ear tag #, but I can tell you how much their calf weighed at weaning and what they had and what day and half of the breed back dates as well.
Also, not added yet, but an important one, is the cow's udder.... did the newborn have a hard time nursing??? too big of teats, empty quarter??
That would be another reason for culling (unless you got lots of time to make sure that calf can nurse and want to be bothered by it).