Protein Synthesis in the Rumen of Bulls given Different Levels of Molasses and Cassava Root

Three bulls (Zebu x Holstein) fitted with permanent cannuale in the rumen and in the duodenum were used to estimate the efficiency of microbial protein synthesis in the rumen, when the dietary carbohydrate consisted of different proportions of sugar (molasses) and starch (cassava root). Freshly chopped cassava forage was given each day as a source of roughage and protein . The flow of digesta through the duodenum and the faecal output were estimated using the inert marker Cr O . A maximum possible value for the synthesis of microbial protein was estimated from the 2 3 flow of crude protein to the duodenum. The apparent fermentation of starch in the forestomachs was 94 + 2% of that consumed, and was not affected by the level of intake of starch. There were no effects of the level of intake of cassava root on the apparent DM digestibility of the ration across the forestomachs or the whole digestive tract. The values for these two parameters were 67 + 22 and 81 + 2% respectively. Assuming that the amount of dietary non-ammonia Npasaing to the duodenum was the same for all diets the maximum efficiency of microbial protein synthesis (g duodenal crude protein/lOOg DM fermented in forestomachs) was estimated This value varied from 4.3 to 12.8 and appeared to be positively related (r = 0.62) to proportion of fermentable substrate in the ration provided by starch. It wee suggested that 2