Transfer of plasma sulfate from blood to rumen. A review

Sulfate of blood plasma recycled to the rumen is potentially an important source of sulfur for rumen bacteria, especially when the diet is low in sulfur, in much the same way as ammonia released from urea and transferred from the blood is a source of nitrogen. Estimates of recycling of endogenous sulfur to the rumen vary considerably among various roughage diets. Transfer of plasma sulfate from blood to rumen is attributable mainly to salivary sulfate, whereas direct flow of sulfate across the rumen epithelium is of minor importance. Regression analyses show that the rate of transfer of sulfate from blood plasma to the rumen for given diets is related to concentrations of sulfate in plasma. It is suggested that during sulfur deprivation, utilization of sulfate recycled to the rumen can be of considerable significance to sulfur economy of the ruminant.