As above lost two or three hogs with blocked urethras ( not my proudest moment) after feeding ewe pellets. From memory after doing the research, it's the high levels of phosphate in ewe feed which calcifies and causes the problem in male sheep.
I'm sure you're system works well, but what about rented land etc where the fences can't altered or a pen made big enough that the first ones in don't loose interest in the treats and turn back even before the last ones get there.
Best thing I have done for calf rearing is build " dens " in the bigger yard out of pallets, tin etc for when the weather gets cold. It's a coat warmer inside them and the calves can go in and out as they choose. Calves have done much better since I've started doing this.