Alfalfa does not cause urinary calculi. Calculi in male goats are caused by too high a phosphorus content in the diet--alfalfa contains way more calcium than phosphorus, making them less likely to get them.
Free choice alfalfa is fine for all goats as long as they are not overeating and getting too fat.
Forgive
I should have stated that I do not have access to fresh/baled alfalfa... all that is available here is the pelleted, cubed & shrinkwrapped"bales" of Lucrene Farms Alfa Supreme - all of which are misted with molasses, and not good for wethers(Molasses is a rich source of potassium which, if fed in excess * , reduce the absorption of calcium, thus upsetting the calcium to phosphorus ratio). * excess being free choice
If what you are giving is just baled alfalfa hay then you should be fine, but if what you are feeding is the pelleted, cubed, or alfa supreme, then you will need to add more calcium to their diets to counteract the potassium.
It's like sprouting grains for the goats vs just giving them the grains. Grains contain anti-nutrients which unless the grains are sprouted will inhibit the good nutrients in the grains from being properly absorbed and processed.