Inadequate uptake of macro-mineral elements in cattle frequently causes economic losses, mainly through clinical disease in the case of Ca and Mg and reduced performance in the case of P and Na. Uptake is a function of mineral intake, solubilization in the digestive tract and absorption of the solubilized fraction. Inadequate Mg uptake is known to be partly caused by fertilizer K, which elevates herbage Ko content and prevents Mg absorption in the rumen. Fertilizer Na, by restricting herbage K uptake offers a means to increase Mg uptake in cattle and could potentially increase the uptake of other minerals.