Sulphur Metabolism and Excretion Studies in Ruminants IX. Sulphur, Nitrogen, and Energy Utilization by Sheep Fed a Sulphur-Deficient and a Sulphate-Supplemented, Roughage-Based Diet

Abstract

Four Merino wethers were each fed a sulphur-deficient, roughage-based ration containing 1'05% nitrogen (79% as urea) and supplying 135 mg sulphur/day. Four other sheep were fed similar amounts of basal ration supplemented with NasS04. This ration supplied 494 mg sulphur/day. Mter 21-day periods the treatment groups were reversed.Supplemental sulphate increased the daily flow of protein nitrogen to the omasum by 2·09 (±0·28) g/day (mean ± S.E.M.) (p<0·001) and changed the nitrogen balance from -2·38 (±0·09) g/day to 0·15 (±0·19) g/day (P<O·OOl). The sulphur balances were changed from -101 (±4·8) mg/day to 86 (±14'6) mg/ day (P < 0·001). The ratio of nitrogen to sulphur stored when sulphate was added to the basal ration was 13·5 (±0·58), therefore a nitrogen to sulphur ratio in the feed narrower than this is necessary for the optimal usage of dietary nitrogen by sheep.The apparent digestibility of organic matter of the diet was increased from 43·8 (±2·59)% to 65·7 (±2'63)% (p<0·01) when sulphate was added to the basal ration. The intake of energy was thereby altered from a submaintenance level of 1065 (±65) kcal/day to an above-maintenance level of 1653 (±68) kcal/day (P<O·OOI). An estimated 10·1 (±6'33)% of the dietary organic matter digested was digested in the rumen on the basal treatment, compared with 74· 8 (± 3·85) % on the sulphur-supplemented ration (p<0·001). The amount of sulphur apparently recycled to the rumen on the basal treat· ment was 192 (±30) mg/day; less was found on the sulphate treatment, due to inefficient utilization of the added sulphur.The output of organic sulphur in faeces was increased (P<O'OOI) by the addition of sulphate to the diet. Urinary excretion of organic sulphur (p<0'001) and ester sulphur (P<O'OOI) was also increased, but the excretion of inorganic sulphate did not change, indicating a limiting supply of sulphate ions for sulphation reactions at these intakes of sulphur.

Ammonium Hydroxide Treatment on Wheat Straw

“…The addition of sulfur to roughage diets generally has increased voluntary intake Siebert, 1972, 1973;Playne, 1969) digestibility of crude fiber (Bray and Hemsley, 1969;Deif et al ,1970;Hume and Bird, 1970;Kennedy and Siebert, 1972;Starks et al, 1954) and energy utilization (Bird, 1972 (Begg and Freney, 1960). Also, moisture stress depresses the sulfur and crude protein content of forages.…”

Transfer of Sulphur to the Digestive Tract of Sheep

“…The efficiency of incorporation of recycled sulphate into microbial protein was thus low,even when the primary limitation to microbial growth on this same diet appeared to be sulphur deficiency (Bird 1972b), and probably reflected the rapidity of absorption of sulphide from the rumen. For example, Bray's (I 969b ) data indicate that the mean time spent by sulphide molecules in the rumen may be as low as 14-31 min.…”

“…The diet was similar to the basal diet of Bird (1972b) and consisted of oat hulls (83 %), starch (6 %), sucrose (6 %), minerals (3 %), and urea (2 %). The mineral mixture was that described by Hume and Bird (1970).…”

“…The rate of synthesis of microbial protein in the rumen of sheep fed low sulphur diets may be increased by supplementation with inorganic sulphate (Hume and Bird 1970;Bird 1972b), with consequent improvement in the retention of nitrogen and energy in the body. End<?genous sulphate recycled from the blood to the rumen is undoubtedly also used in this manner.…”

Digesta Flows in Sheep Fed Poor-Quality Hay Supplemented with Urea and Carbohydrates

“…Bird (1972) showed that with S-deficient, urea-oat hulls diets, ruminal degradation of organic matter was limited, compared with S supplemented diets. It is not certain, however, that in the present study S was the primary limiting factor, especially because it was demonstrated with sheep that when the level of digestible energy was sufficient urea supplementation still enhanced microbial growth, even with N to S ratios of up to 60 to 1 (Elliott and Armstrong, 1982).…”