Studies on magnesium in ruminant nutrition

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Abstract
1. In Expt 1 balance studies were carried out with six wether sheep receiving chopped hay and concentrates and given, 0, 5, or 101. water/day by intraruminal infusion. Allocation to two 3 x 3 latin squares was arranged to allow calculation of main treatment and residual effects. 2. Infusing 101.water/day increased the total daily urinary output of magnesium, phosphorus and sodium by 31, 45 and 100% (P<0.05). Faecal losses of Mg, and P tended to decrease correspondingly and with both elements retention remained positive but retention of Na became negative (P < 0.05). 3. Residual effects were not detected, and infusing 5 1. water/ day generally produced intermediate and non-significant effects. 4. When pellets made from dried, ground, young spring pasture or ccncentrates rich in Mg were included in the diet of four wethers in Expts 2 and 3, infusions of 101. water/day produced much greater decrcases in faecal losses and retentions of Na and K and greater increases in the urinary excretion of those elements than those found in Expt I. Effects on Mg, P and Ca balance were similar to those in the main experiment. 5. The biological significance of these results and relationships between the observed effects and the aetiology of hypomagnesaemic tetany are discussed.