Plus, my experience is that, once a ewe has had mastitis, even if her udder does come back to looking and feeling normal, it is likely to not be as productive in future, which means hungry lambs, which in itself can cause mastitis (through their interminable grinding on at an empty udder), which is then highly likely to spread (as the hungry lambs pinch milk off other ewes...), and/or you end up with a dead lamb, or a lamb you have to rear on a bottle or foster.... So, even though you can get ewes who recover fully, in practise it is, in my opinion and that of many sheep farmers, best for the flock to cull - or retire - any ewes who've had mastitis once they've reared their current lambs.