I found it didn't pay for me when I tried it, only way it pays I think is to hold them through winter and get the green grass fever in march/april.. Grain and supplements are expensive out here, so unprofitable right off the bat, the weight loss for a week is hardly recouped in the next couple weeks, cost of vaccines, risk of illness and death, worsening road conditions to ship (for me to the sale barn, and from the sale barn to feedlots) doesn't help anything either if you get into November...
I've found what work for me is wean when the oldest are around 7 months and they come off good pastures, and there's lots of grass left for the cows to put condition on before winter (it's said that a milking cow and a good calf eat like 3, and I've found that to be true), once I've shipped the calves, a pasture that would have been 2 weeks of food is suddenly 4-5 weeks worth, and if I can graze til christmas (if nature doesn't give me too much white crap), my hay sales will more than make up for the difference in the price of calves