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This study assessed the effects of cellulase, xylanase, and their mixture (1:1, v/v) on in vitro rumen fermentation of five mixed rations with different maize silage (F) to concentrate (C) ratios (0F:100C, 25F:75C, 50F:50C, 75F:25C, 100F:0C). Samples were incubated using rumen inoculum from Brown Swiss cows fed ad libitum a total mixed ration of concentrate and alfalfa hay (1:1). Gas production (GP) was recorded after 2, 4, 6, 8, 10, 12, 24, 36, 48, and 72 h of incubation. Interaction effects (P < 0.0001) were observed between type of ration and enzyme for discrete lag time prior to GP. Ration type affected asymptotic GP (linear and quadratic, P < 0.0001) and in vitro GP at 24 h onward. Moreover, rations affected pH (linear and quadratic, P < 0.0001), dry matter degradability (quadratic, P = 0.05), metabolizable energy (linear, P = 0.038), short-chain fatty acids (linear, P = 0.0005), gas yield from truly digested dry matter at 24 h (linear, P = 0.0026), and microbial crude protein yield (linear, P = 0.0264). The most effective rations for in vitro GP during different times differed between different measured parameters. Enzyme administration was more effective when the ratio of maize silage was increased.

In the present study, sensitive and mutant colonies of some ruminal bacterial species isolated from sheep, cattle, and buffalo were detected. We counted and considered \"mutant colonies\" the bacterial colonies grown in the clear inhibition zone in the Kirby-Bauer disk diffusion susceptibility test. Detected mutant colonies were higher in buffalo than in cattle and sheep. Duricef and metronidazole caused no mutations in any species. The others formed mutant colonies, where roxithromycin = polymyxin = chloramphenicol = gentamicin < erythromycin < vancomycin < piperacillin = cefotaxime < streptomycin < cefoperazone < ciprofloxacin < amikacin. Sheep had the highest number of sensitive isolates, and the number of sensitive isolates was dramatically lower in cattle and buffalo. There were no sensitive isolates with the antibiotic metronidazole, and there was a low number of sensitive isolates with duricef. The other antibiotics had more sensitive isolates (gentamicin = ciprofloxacin = amikacin > streptomycin = piperacillin > erythromycin > vancomycin = cefoperazone = cefotaxime > roxithromycin > polymyxin > chloramphenicol). The number of sensitive isolates of the different ruminant species for all the antibiotics was highest in buffalo, followed by cattle and then sheep (P < 0.05). We could conclude that subtherapeutic antibiotic use in ruminant feeding may lead to the formation of antibiotic-resistant mutant colonies, making their subtherapeutic effect nonexistent.