In vitro studies on non-protein nitrogen utilization by rumen microflora. I. Effect of nature of energy and minerals using phosphorus-32 as a label of microbial growth

The effect of the nature of carbohydrates and minerals on microbial growth has been studied in vitro to intensify rumen microbial protein synthesis from non-protein nitrogen. The two methods used are a classical one based on decrease of ammonia in the incubation medium and one measuring 32P incorporation in microflora. The nature of starch greatly influences urea utilization. Maize starches with high amylose content (50-60%) and B-type X-ray diffraction pattern allow a lower rate of urea utilization than starch from normal or waxy maize. Large starch granules, such as those found in some varieties of tropical tubers, also reduce urea utilization. Among the tropical tubers studied yam Cayenensis and canna Edulis give lower urea utilization than cassava and yam Dumetorum. However, this can be improved by processing; extrusion of maize and pelleting of tropical tubers promotes urea utilization. The effect is greatest when the proportion of urea to processed cereal is about 4-5%. Protein synthesis is not further improved when the percentage of urea exceeds 12%. Adding phosphorus and zinc to the incubation medium does not affect urea utilization. However, the addition of sulphur in the form of sulphate improves urea utilization with both natural and purified diets. (author)