Urinary calculi formation in sheep on high wheat grain diets

Abstract

The effects of calcium, phosphorus and magnesium contents of diets containing different proportions of wheat grain to roughage on the excretion of minerals involved in urinary calculi formation by sheep, were examined in three separate studies: the first, with six sheep, determined the effects of increasing the percentage of wheat grain in the diet on the digestibilities of Ca, P and Mg, the excretion of these three elements in urine and on the propensity of the diets to form calculi; the second involved two sheep and studied the effects of supplementing a 90% grain diet with CaCO3 and roughage on faecal and urinary excretion of Ca, P and Mg; the third was carried out using four sheep fed on a 75 % grain diet and examined the effects of supplementation with extra P, Ca and roughage on Ca, P and Mg excretion. Urinary P concentration was directly correlated with the formation of calculi. Plasma inorganic phosphorus (P,) increased when grain in the diet was 75 % or greater and this led to increased urinary P excretion. The addition of CaCO3 reduced urinary P without large changes in plasma P1 and increased the faecal output of P. Extra roughage added to high grain diets reduced the digestibility of both Ca and P and the plasma concentration and urinary excretion of P. The significance of these findings for the prevention of urinary calculi in sheep is discussed.