Effect of roughage level in complete feed on the rumen environment in crossbred cows

The effect of iso-nitrogenous diets with either high roughage (HR) or low roughage (LR) containing 30: 70 or 70: 30 concentrate to roughage ratio respectivly, on the pattern of rumen microbial enzymes and the degradation pattern of these diets, was evaluated in four rumen fistulated, dry, sterile crossbred cows (404 ± 28 kg body weight), in a 2x2 switch over design.

Total protozoa number was higher (P<0.05) in the rumen of cows fed LR diet as compared to those fed HR complete feed. Irrespective of the fiber level, the entodiniomorphs predominated (93–94%) the protozoa population as compared to holotrichs (4–7%). Amongst entodiniomorphs, the entodinium predominated. The activity of carboxy methyl cellulase (CMCase), micro crystalline cellulase (MCCase), xylanase and P-glucosidase (irrespective of fraction of rumen contents) was higher (P<0.05) in crossbred cows fed HR based complete feed, where as activity of amylase and protease was higher (P<0.05) in-group fed LR complete feed. Irrespective of roughage level, the activity of fiber degrading enzymes was highest (P<0.05) in particulate matter (80.2%) followed by cellular (13.8%) and extra-cellular fluid (6.0%). The ammonia -N and total NPN contents were lower (P<0.05) in LR group indicating better utilization of ammonia -N in the presence of higher availability of soluble carbohydrates in this group thereby resulting in higher (P<0.05) TCA -N.

The kinetic parameters of DM, NDF and CP degradation, revealed that the insoluble but potentially degradable fraction in the LR diet, was not only significantly (P<0.05) higher, but also degraded at a faster rate (P<0.05). Presence of lower (P<0.05) amount of un-degradable fraction resulted in higher (P<0.05) effective and true degradability of LR diet. The rumen fill values, for DM were observed to be higher (P<0.05) in the HR diet, indicating its low potential for voluntary DMI. The results conclusively revealed that roughage level in the diet modify rumen microbial population, leading to changes in the pattern of microbial enzymes responsible for digestibility of nutrients.