I wouldn't be so quick to get rid of a cow that doesn't nurse a calf. A lot of factors have to be considered, but any ways when we have a cow that loses her calf we try to put her in with a cow that just calved, as long as the momma cow tolerates the company. This helped us one year when a heifer lost her calf and another cow had twins. The heifer was able to help milk the Shorty twins and when it came to wean, they both were up at the fence voicing their displeasure.