I do calf rearing in the lambing shed after I've finished using it for shearing in May, selling the calves as potential suckler cows in February, so leaving the shed empty for lambing again. It's a pole barn so ventilation is very good. BUT I get top quality British Freisian x British Blue heifer calves from a local dairy farm that's meticulous about ensuring calves get sufficient colostrum and gives us buckets of the stuff when we pick them up. We use our own hay and best quality milk powder. We invested in cattle hurdles, a secondhand dehorning crate and calf buckets. We've now become known for top quality calves and make a reasonable profit when they go to auction. It helps a lot if you really like calf-rearing (which I do!)