I absolutely agree with Denny that outside calves are not worth it. If a set of twins is born early they are a great source. I keep a few old cows if they are bred to calve early in the season and go grab one of those calves when needed and then ship the old cow in early summer after she adds...
I use 1/4 cc xylazine and 2 cc's ace IV in the cow's tail vein. Wait about 5 minutes and start the new calf. You don't have to fight the cow and while she is waking up she sniffs the calf and thinks it is hers by the time she wakes up. It works almost every time with very little work.