Nitrogen conversion and apparent intestinal amino acid absorption in youngbulls fed isonitrogenous diets with different nitrogen sources

The experiment was carried out on 10 bulls of about 120 kg live weight equi pped with rumen cannulas and re-entrant cannulas in the proximal duodenum a nd terminal ileum. The bulls were given a diet of maize whole plant meal, p otato starch and mineral mixture. The diet was supplemented for group I wit h groundnut oilmeal (60% of dietary N), for group II with groundnut oilmeal (10.5% dietary N) and urea (48% of dietary N), and for group III with urea (58% dietary N). Diets I, II and III contained, according to the INRA syst em, 15% CP in DM; 234, 196, 186 g PDIN; 227, 158, 145 g PDIE, and 2.14, 2.1 1, 2.11 UFV, respectively. Daily feed intake was 2.25 kg. The ammonia-N level in the rumen fluid 2 h after feeding was 8.2, 15.1 and 24.5 mg/100 mi in animals of groups I, II and III, respectively. The amount of N entering the duodenum was 20.1; 22.1 and 18.0 g, leaving the ileum 9. 7, 10.4 and 7.3 g/day/kg of feed intake, in the respective groups. The appa rent duodenal-N absorption from the small intestine was 52, 53 and 59%, res pectively. Total amino acids (g/day/kg feed) ingested with feed equalled 128, 62 and 4 9; entering the duodenum 107, 113 and 92; leaving the ileum 43, 48 and 32; absorbed from the small intestine 64, 65 and 60 in groups I, II and III, re spectively. The apparent intestinal absorption of most amino acids entering the duodenum was from 50 to 70% in all groups, but absorption of cysteine was markedly lower, 25-40%. The amount of lysine absorbed from the small in testine in group I was similar to the amount ingested, but exceeded this am ount by 2.4 and 3 times in groups II and III. Absorption of methionine was two times higher, indicating considerable conversion of dietary N in group II and III into microbial amino acids.