The mineral metabolism of sheep fed high‐ and low‐magnesium selections of Italian ryegrass

Two experimental populations of Italian ryegrass selected for high and low magnesium content were established as swards, harvested fresh daily and offered to sheep. Chemical analysis of the crops showed a 44% higher Mg and a 22% higher Ca concentration in the high‐Mg selection but no significant differences between the selections for the other minerals. Blood and rumen contents were sampled throughout the feeding period and voluntary intake, digestibility and mineral balances for Na, K, Mg, Ca and P were determined. Magnesium intake, apparent availability and retention were significantly greater with the high‐Mg selection. There were no significant differences in the plasma‐mineral concentrations and all were within the normal range. Rumen fluid from animals fed the high‐Mg selection had a higher proportion of soluble Mg and a higher Na:K ratio in the supernatant liquor.