Charlie,
You brought up important points.
I would like to respond to two.
“Why do we use weaning weights?”
We sell calves by the pound and that is when most producers sell their calves.
When universities decided that since we sell pounds, the more the better, in 1969-70, the weaning weight race was on. NO thought of the cost to increase weaning weight. It was a given, apparently, that it was FREE. And no university professor at the time had sat in a sale barn and watched big calves sell for less per pound than smaller calves.
A small difference in the “90 days for a calf to get half his nutrition from grass.”
Research conducted at New Mexico State University indicates that after about 60 days of age, average daily gain is similar for both high and low milk consuming calves (Ansotegui 1986). The difference here is the environment they were raised in. NMSU is in a very arid climate. Plants there have more value per pound eaten than those in a lush environment. Where might the dividing line be in quality of plants? Minor point, but still a difference.
Chip Hines
NE CO