Kinetics of Dietary Nitrogen Fed Optimum and Sub-Optimum Diets in Cattle and Buffaloes

The studies were conducted to compare N kinetics in rumen fistulated 4 calves and 4 buffalo-calves using 2 test diets I and II, randomly divided into 4 groups 1 through 4. Calves of groups 1 and 3 were fed optimum test diet I and those of groups 2 and 4 (test diet II) received 65 per cent less DCP and 25 per cent less TON, constituted from concentrate mixture, oat hay and wheat straw. Subsequent to digestibility trial, 2 hourly feeding was practiced for 12 hours of the day for 9 days, after which ¹³N-ammonium sulphate and ⁵¹Cr-EDTA were injected intraruminally. The digestibility studies revealed that CF digestive coefficient was 70.29 per cent with test diet I as compared to 57.01 per cent with test diet II, without showing any difference between the species. N balance studies revealed N retention as 17.47, 7.15, 32.44 and 14.54 g N per day in groups 1 through 4, giving figures of 30.40, 26.04, 43.06 and 40.55 as per cent of N intake. Ruminal pH did not vary between test diets and between species at different hours showing normal rumen function and buffering capacity. The TVFA levels in SRL estimated at different timed intervals also did not show any particular trend. The ruminal NH3-N concentration showed a plateau withmean values of 13.38 and 12.54 mg per 100 ml SRL in groups 1 and 3 and 6 37 and 6 54 mg per 100 ml SRL in groups 2 and 4 respectively Using ⁵¹Cr-EDTA the estimated rumen volume was 9.22 12 88 12 95 and 11 46 litres; rumen fluid outflow rates 15 69 13 90 21 47 and 18 561/day in groups 1 through 4 respectively The corresponding values for ruminal-NH₃ pool size were 1 23 0 82 1 62 and 0 75g N and for ammonia outflow from rumen fluid were 2 10 0 89 2 69 and 1 21 g N ner day which were related to N intake The data further revealed that the mean ruminal ammonia pool size values estimated by either ⁵¹Cr-EDTA or ¹⁵N were almost similar Ruminal ammonia irreversible loss as per cent of entry rate ranged from 57 22 to 63 04 in optimum fed groups and was less than the values in groups 2 and 4 Incorporation of ¹⁵N ruiminal amminia into suspended in bacteria was on an average. 42.13 per cent which was again less than the per cent incorporation in groups 2 and 4 without snowing any species difference, but exhibiting preferential utilization under stress condition of low N intake. It was apparent from urinary N derived from ruminal ammonia that perhaps N utilization was better only at the tissue level in buffalo-calves as compared to calves.