Urinary calculi I a bladder stone. Because of the way a wether's urethra is shaped and sized they can become lodged plug them up. Is the animal not peeing at all? Can a lump of stone be felt in the penis? The most common spot for the stones to lodge is right above the pizzle. In that case, cutting off the pizzle will let the stones free. There are usually more stones in bladder however and treatment with Ammonium Chloride would be suggested. Do they have AC by chance?
They very well may need a good livestock vet.