Hypomagnesaemia in milking cows: intake and utilization of magnesium from herbage by lactating cows.

During 1958-60, 11 Mg balance trials were carried out with 39 lactating Friesian cows, which were fed indoors on a winter ration in 1 trial or on herbage freshly cut from pastures with different fertilizer treatments in the other trials. Average daily Mg intake was 33.08 g. for the winter ration and 16.62 g. for herbage, 17% of which was 'available', i.e. absorbed. Average Mg excretion in urine was 1.77 g., Mg excretion in milk 1.77 g./cow with an average content of 0.12 g./kg. milk, and Mg retention -0.5 g. Hypomagnesaemia occurred only when Mg excreted in urine was