The reason you would feed the Caprine magnum-milk mineral is because you are already feeding lots of alfalfa and high calcium comtaining feeds to lactating does other wise you would always feed a mineral with a 2:1 ration, You don't ever want your phosphorus to be too high, when feeding to any males.
We feed a 2:1 calcium to phosporus ration in our feed and mineral to all our goats regardless of the stage of growth, gestation or lactation.