Feeding of grainless diets containing different nitrogen sources to crossbred growing bulls: effects on rumen fermentation pattern, microbial enzyme activity and ciliate protozoa population

The effect of feeding grainless concentrates containing different supplemental nitrogen sources along with wheat straw-based diets was studied on rumen fermentation pattern, microbial enzyme activity and protozoa population. For the purpose five fistulated 18 months aged crossbred bulls (Bos indicus × Bos taurus) were used in a 5 × 5 Latin square design. The animal fed the control diet, received barley 300 g/kg dry matter (DM) in the concentrate mixture (CM1) as a source of grain, whereas other concentrates contained only wheat bran (CM2) or wheat bran supplemented with 25 g urea (CM3), 215 g groundnut cake (GNC) (CM4) or 270 g mustard oil cake (MOC) (CM5)/kg DM, as a source of supplemental nitrogen. The bulls were fed concentrate mixtures at 1 kg/100 kg of their body weight. Each feeding period lasted 21 days followed by rumen liquor collection. Neither the presence of barley nor the nitrogen from different sources in the concentrate mixture did influence the daily dry matter intake (DMI) by the bulls. The DMI per unit of body weight was similar in all the groups. Feeding of barley-based concentrate (CM1) and GNC supplemented grainless diet (CM4) significantly decreased the rumen pH at 4–6 h post-feeding. The total volatile fatty acid (VFA) concentration was the highest (P < 0.01) in animals fed CM1 and higher (P < 0.05) on CM4 than on CM5. However, the dietary treatments did not influence the molar proportion of acetate, propionate and butyrate. Supplementation of urea in the concentrate mixture (CM3) resulted in the highest (P < 0.01) ruminal ammonia-N (NH3-N) concentration. The ruminal total-nitrogen concentration was the highest (P < 0.01) in animals fed on CM1 and higher (P < 0.05) on CM4 than on CM5. In the strained rumen liquor (SRL) α-amylase activity was increased significantly when the animals fed CM1. The endoglucanase activity was significantly decreased (P < 0.05) in animals fed on CM4 and CM5 as compared to that of CM1 fed bulls. Supplementation of oil cakes or urea to the wheat bran-based grainless concentrates significantly increased the protease activity. Urease activity was significantly increased in response to the dietary urea. Total ciliate population did not differ in SRL of animals fed on CM1, CM2 and CM4, which were significantly higher to that of those fed on CM3 or CM5. Addition of MOC seemed to depress the overall rumen fermentation. The rumen fermentation pattern of bulls fed wheat bran-based grainless concentrate mixture with supplemental nitrogen, urea or oil cakes, was almost similar to that of those fed on grain-based concentrate at 1 kg/100 kg of body weight, when wheat straw used as basal roughage.