Efficiency of N utilization under four feeding systems with varying frequency of feeding was studied with growing crossbred buil calves fed on rations consisting of wheat straw and concentrates to provide the recommended level of protein and energy for 500 g/d gain in body weight. N intake and digestibility co-efficients of various proximate constituents did not differ (P > 0.05) under the four feeding systems offering daily concentrate allowance once (FS-1), twice (FS-2), mixed with wheat straw (FS-3) and in eight fractions at hourly intervals (FS-4). The urinary N excretion (g/d) was found significantly (P < 0.01) lower (29.9 ± 1.6) on FS-4 as compared to those observed on FS 1 (38.9 ± 0.5), FS-2 (37.8 ± 1.0) or FS -3 (37.3 ± 0.5) resulting in a significant (P < 0.01) difference in per cent retention of absorbed N (FS-1: 33.9 ± 3.7; FS-2 :35.5 ± 0 7; FS-3 : 36.7 ± 1.6 and FS-4 : 46.0 ± 2.6).
The rumen fermentation pattern under 4 different feeding systems indicated that the peak NH3-N concentration at 4 h post-feeding was 25.4 ± 1.8 and 20.5 ± 1.7 mg N/100 ml SRL and TVFA peak concentration at 6 h was 144.3 ± 3.8 and 138.8 ± 4.3 meq/L, respectively on FS-1 and FS-3. Under FS-2, the peak NH3-N concentration (26.3 ± 1.6 mg N/100 ml SRL) comparable to FS-1 was attained at 2 h post-feeding itself, because water was offered after drawing this sample. However, the subsequent decline of NH3-N concentration was very sharp and TVFA concentration at peak remained much lower (115.5 meq/L) than FS-1 and FS-3. The concentration of NH3-N under FS-4 ranged from 8.8 to 11.8 mg N/100 ml SRL and TVFA concentration increased slowly with hourly feeding concentrate allowance in 8 fractions. These differences in NH3 and TVFA concentration did not influence significantly the pattern of change in pH of SRL. These results indicated that increased frequency of concentrate feeding altered the concentrations of various N fractions in the rumen which had much bearing on the efficiency of feed protein utilisation.
