Nitrogen Dynamics in the Rumen and Abomasum of Sheep Determined with 15n-labelled Ammonia Or

An experiment was carried out to investigate the dynamics of nitrogen (N) in the rumen and abomasum of rumen and abomasum-cannulated sheep using 15N dilution techniques. The 15N tracer was administered into the rumen as 15N-ammonia or 15N-labelled duckweed and the transfer of the 15N label to various N pools was followed. Flow of digesta from the rumen into the abomasum was ascertained by double marker technique with cobalt and acid insoluble ash as liquid digesta and particle digesta marker, respectively. Results showed that the average of rumen water volume was 4.5 l ± SEM 0.57 and the mean water flow through the abomasum (8.6 ± 0.45 l/d) was higher than outflow from the rumen (7.4 ± 0.55 l/d). Nitrogen intake tended to be higher, but total-N passing the abomasum tended to be lower when the sheep were infused by 15N-ammonia than when they were ingesting 15N-duckweed. The ammonia concentration in abomasal digesta was about 93 mg N/kg and non ammonia N (NAN) was about 1.58 g N/kg. The rates of flow of total-N as ammonia-N and as NAN did not differ (P>0.05) between animals or diets, with means (± SEM) of 57.7 ± 0.96 and 964 ± 2.13 mmol/d (or 0.81 and 13.5 g N/d), respectively. About 34-59% of the dietary N was removed from the rumen as ammonia (absorbed and in digesta). The enrichments of rumen ammonia N appeared to have reached plateau values after about 10 h of 15N-ammonia infusion. The percentage of bacterial-N derived from ammonia-N (from the period of 15N-ammonia infusion) was 53.63 % (ratio of plateau enrichments) and thus 37.47% of bacterial-N was derived from NAN sources in the rumen. The total 15N flow through the abomasum was higher (P<0.001) when 5N duckweed was given rather than 15Nammonia (2.40  0.02 versus 1.29  0.02 mmol/d). The 15N in NAN flowing to the abomasum (mmol/d) was also significantly higher (P<0.001) when 15N-duckweed was given rather than 15N ammonia, with means of 2.31  0.02 and 1.16  0.00, respectively. The flow of 15N in ammonia, on the other hand, was lower (P<0.01) when sheep ingested 15N-duckweed than when they were infused with 15N-ammonia (0.09  0.00 v. 0.13  0.09 mmol/d).