Efficiency of bacterial protein synthesis in the rumen of sheep receiving a diet of sugar beet pulp and barley

Eight sheep fitted with both rumen and duodenal re‐entrant cannulae were used to investigate the digestion of a diet consisting of 60% molassed sugar beet pulp and 40% ground barley. Molar proportions of acetic acid in the rumen varied from 55 to 66%, of propionic acid from 15 to 26% and of butyric acid from 12 to 19%. On average, 69.1 ± 1.2% of the dietary organic matter was digested in the rumen and 89.9 ± 0.4% in the whole digestive tract. Corresponding figures for gross energy were 64.4 ± 1.4% and 87.4 ± 0.4%, for cellulose 82.8 ± 1.4% and 86.3 ± 0.8% and for α‐linked glucose polymers were 91.6 ± 0.9% and 100 ± 0%. There were only small differences in the extent of digestion of these constituents in the rumen between animals and the mean production of total short‐chain fatty acids was 55.5 ± 1.6% of the digestible energy. The mean daily amount of nitrogen entering the duodenum was 11.1 ± 5.1% greater than the dietary intake and the apparent digestibility of nitrogen was 76.7 ± 1.0%. Calculation of bacterial protein using α‐±‐diaminopimelic acid as a marker, indicated that bacterial protein constituted about 80% of the total protein entering the duodenum and that the average efficiency of rumen protein synthesis was 14.31 ± 0.75 g crude protein/100 g OM “disappearing” in the rumen. With the exception of one animal in which the rumen ammonia concentration was especially high, the efficiency of protein synthesis varied between animals over only a narrow range and there was no evidence that efficiency was influenced by variation in the pattern of fermentation in the rumen.