Models of rumen sulphur metabolism in sheep

A preliminary investigation (Part III) was carried out to investigate the losses of volatile sulphur compounds from sheep maintained on a high sulphur ration (total N = 1.980% of dry matter, total S = 0.395% of dry matter, N/S = 5/1), following intraruminal administration of sodium [ 35 S] sulphate. Sheep were fed their rations at one hourly intervals with urea and inorganic sulphate being virtually the major sources of nitrogen and sulphur respectively in order to establish steady-state conditions in the rumen, that is constant rumen sulphide concentration and pH were maintained under these conditions. The first experiment (Part IV) was conducted with a low sulphur intake (total N = 1.417% of dry matter, total S = 0.159% of dry matter, N/S = 8.9/1) in order to gain experience with modelling and test the proposed model. For the same purpose the sheep received a high sulphur ration (total N = 1.826% of dry matter, total S = 0.321% of dry matter, N/S = 5.7/1) in the second experiment (Part V). Because of the anaerobic conditions predominant in the rumen, protein synthesis is mainly limited by available energy. In the third (Part VI) and fourth (Part VII) experiments the effect of energy intake on microbial protein synthesis and absorption rate from the rumen was studied. In the third experiment, the sheep were maintained on a high sulphur. ration (total N = 1.753% of dry matter, total S = 0.312% of dry matter, N/S = 5.6/1) and 15% of the oat hulls were replaced by starch. In the fourth experiment, the sheep received a high sulphur ration as previously (total N = 1.681% of dry matter, total S = 0.302% of dry matter, N/S = 5.6/1) and 30% of the oat hulls were replaced by starch. During the course of these experiments, recent marker techniques were used to study the flow of digesta and the sulphur flow rates from the rumen.