[landroverroy]

 It's actually high magnesium that causes stones in the urethra of male sheep. It is important, therefore to ensure they always have a good supply of clean water, as this reduces the risk.

[andywalt]

its really good picking up these tips, I wold have had no idea about this one !     the 18% I feed is labelled ewe plus 18%

in fact here is the link   http://www.snackandtack.co.uk/farm-animals-c43/sheep-c93/attlee-ewe-nuts-p801

as its labelled ewe nuts hopefully ok for tups, it does say its a great general purpose feed.......  any comments?

[landroverroy]

 I've only ever once had a male sheep with a urinary stone and that was in a particularly fine Ryland ram lamb, about 6 months old, and he was on grass with a mineral lick available. He was in agony and we had to have him put down.   
 However, I normally keep the tup in with my ewes till after lambing and he therefore eats (in great quantities) all the good food and minerals that they get and with no ill effect.
 I therefore believe that there are some rams that are prone to stones, whatever you do, - just like humans. You can therefore only help reduce the risk by ensuring a good and clean water supply and I have since heard that giving cider viegar is helpful.