*Present address : Dairy Cattle Nutrition Division, National Dairy Research Institute, Karnal 132 001, India.
The studies were conducted on two non-lactating Danish Friesian cows (775 kg) fitted with a permanent rumen fistula and a re-enterant cannula in the duodenum about 50 cm behind the pylorus. The animals were fed on five isocaloric rations containing 1 per cent urea (R1), 23 per cent urea (R2), 45 per cent urea (R3), 15 per cent soybean meal (SBM) (R4) and 25 per cent SBM (R5), one after the other In a switch over manner, alongwith molasses (5 per cent) and NaOH (4 per cent) treated barley straw which were common to all rations. The CP per cent In the rations R1 to K5 were 83,13.0, 19.9, 12.6 and 19.4 respectively, thereby making ration R2 isonitrogenous with rations R4 and ration R3 with ration R5. DM intake and DM digested in the rumen were similar for all rations. On urea based ration (R1 to R3), the essential amino acids supply to duodenum was 2.64 to 8.57 times higher than present in feed. This was 1.04 to 1.48 times more on R4 and 0.75 to 1.10 time higher on R5 than feed amino acids. There was a net increase of all essential amino acids (g/kg) OM digested in the rumen, g/kg DM intake), the increase being higher for R4 than R5. The differences of net amino acid synthesis between R2 and R4 varied from 2.4 to 14.0 g/kg OM digested in the rumen. The greatest difference being for leucine, which was followed by lysine, valine, iso-leucine, phenylalanine, threonine, histidine and methoinine.
