Sulphur metabolism and excretion studies in ruminants. IV. Cystine and sulphate effects upon the flow of sulphur from the rumen and upon sulphur excretion by sheep

Abstract

In a 4 x 4 Latin square design experiment, sheep were fed on a basal ration which supplied 0.61 g sulphur per day, or the basal ration supplemented with 1.4 g inorganic sulphate sulphur, or 1.4 g cystine sulphur, or 1.4 g sulphate sulphur plus 1.4 g cystine sulphur per day. All forms of sulphur supplements increased the daily flow of protein sulphur from the rumen to the omasum (P < 0.05) above basal. Only the cystine treatments increased the flow of sulphide (P < 0.005), ester sulphate (P < 0.005), soluble organic sulphur (P < 0.05), and cystine (P < 0.05), and increased the ruminal sulphide concentrations above basal (P < 0.005). From 7.0 to 12.6% of the added cystine was not degraded in the rumen. In three animals less than 3 % of the added sulphate, alone or in combination with cystine, passed unchanged to the omasum. The fourth animal (67) differed from the others (P < 0.05): the added sulphate was poorly reduced in the rumen, and 62% reached the omasum unchanged. The sulphur composition of the digesta collected from the omasum was: protein sulphur, 55-70%; soluble organic sulphur, 13-22%; inorganic sulphate sulphur (excluding sheep 67), 2.2-2.6 %; ester sulphate sulphur, 1.8-3.4 %; and sulphide, 0.4-28%. Excluding sheep 67, 36% of the dietary sulphur was absorbed from the rumen when the sulphur was added as sodium sulphate or as cystine, and 50 % when added in both forms together. There was a net addition of 0.45 g sulphur per day to the rumen on the basal diet. The influence of the amount and the form of the dietary sulphur on the excretion of faecal and urinary sulphur fractions is discussed.