If you are getting 140 lb. calves or anything close to it out of Angus cows, it would seem to me it's genetic. Feeding too much especially during the last trimester can add weight to a calf, but 10 lbs would be about as much as you could expect from nutrition. I have had a 98 and a 96 lb calf this winter out of angus and that's the heaviest I have ever had. But they are out of a different bull than I have used before. Are your bulls pure bred Angus ? Were these cows A.I.'d. Maybe the semen was mislabeled. As far as per cent live births, that will vary with every herd. Out of the last 100 I have weaned 99, but, we have a small herd, we are 100% AI so I know the genetics and every due date, and my wife would say I spend too much time with them.