I get mine weaned for 30+ days and eating very well and sell them where they feed them something similar before the sale. For me its OKC. Its a long drive from my place but they keep your group in a smallish pen where they have plenty of a decent feed and fresh water. Since they are penned with the group they are used to and not commingled, they have very little stress. I sold a group in June that lost less than 1 1/4%. They weighed out at the farm at 12,238 lbs on Saturday afternoon, hauled early on Sunday and were sold on Monday afternoon. They split the group but the total was 12,105 lbs. That is the best I have done. I am usually in the 2 to 3% range.
Selling at the sale barn is much more difficult. They need to be long weaned and healthy. It also helps if you can take them in just a couple hours before they sell. Taking them in the day/night before will cost you 3 to 5%. Its not unusual for a calf weaned on the trailer to lose 10%.
I am amazed at the number of people that sell off the farm where the buyer hauls the calves to a feed store or something to get weighed and then deducts another 2% for shrink. Calves will lose 3% just getting penned and loaded. Add on the additional 2% and you gave the buyer $40 a head. The calves if healthy will recoup that weight very quickly when put on feed and water at the end of their trip. At OKC they stay in their small pen with feed and water until they head to the sale arena. They are weighed just before they enter and that is the weight you get paid for.
Weaning for at least 30 days is the best bet no matter where they sell. They also need to know how to drink from a water trough. Sounds stupid but very important when its hot.