Sulphur metabolism in sheep. III. The movement of blood inorganic sulphate across the rumen wall of sheep

Abstract

The movement of intravenously injected sodium [35S]sulphate into the rumen was studied in three sheep in which the normal rumen digesta had been replaced with buffer solutions hypotonic, isotonic, and hypertonic to blood. It was shown that inorganic [35S]sulphate was transferred to the rumen by passage across the rumen wall and that the rate of passage of sulphate was apparently increased by the influx of water into the rumen. Only 0.3–1.4% of the injected [35S]sulphate passed into the rumen by this route over a 4 hr period. It was suggested that the utilization of recycled urea nitrogen may be severely limited in sheep on low sulphur and low nitrogen intakes unless sulphur is recycled to the rumen by other routes or in other forms across the rumen wall. Mixed saliva was collected and analysed and the total sulphur content was found to range from 16 to 43 µg/ml. An average of 79% of this sulphur was present in the residual (protein) sulphur fraction. The sulphate space (extracellular fluid volume) was calculated for each sheep from the dilution of the injected [35S]sulphate. The sulphate space, calculated from the dilution of 35S 30 min after injection, averaged 27% of the body weight. For each sheep the volumes calculated from three determinations lay within ± 5 % of the median value.