Oakridge in the thread just above has a modified  early weaning program.  (Are they ready to Go)  Look at his photo's. Perfection.

I personally like to early wean at no less than 300#  That's not to say less cannot be done. My death loss almost always will be the lightest.  I seen the freshest best 270# calf die.   Fly weight calves are in the high risk category.  One need to do everything to make it work.  You are far enough north that heat may not be a concern but heat and dust, even inside a barn all shorten the time it takes for sickness to become sever.  One has to be quick with a needle and have supply of  quality meds on hand.  They can change in 12 hours.  They take twice a day feeding and evaluation.  Good quality long stem grass hay really helpful. 

If possible feed and dry the cows up even 3 weeks can make them bring more when sold.  We actually have these cows on feed prior to weaning and the calves line up and eat thus also helping with early weaning. The marketing of kill cows completes a cow calf operations circle. It has been proven that kill cow markets top out just prior to July 4 treads water till Labor Day then go down till Christmas. Thus is it a good idea?  Yes if you want to make money in the cow business. 

We have done everything in the books to make whats called the Last Calf Heifer Program work.  Calves go right back with full season calves raised by the standard cow herd.