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. Effect of mechanical processing of corn silage on in vitro ruminal fermentation, and in situ bacterial colonization and dry matter degradation. Can. J. Anim. Sci. 87: 259-267. Rumen fermentation and bacterial colonization of mechanically processed corn silage were evaluated in a series of in vitro and in situ experiments using ruminally cannulated cows. Data from rumen-simulated continuous culture (Rusitec) showed that total VFA concentration was increased (P < 0.001) by feeding processed corn silage, while pH was reduced (P < 0.001) and ammonia nitrogen remained unchanged (P > 0.05). Mechanical processing enhanced the in situ rate and extent of dry matter disappearance for corn stems and kernels, respectively (P < 0.05). It also enhanced in situ, the initial attachment of rumen bacteria responsible for corn digestion, as monitored by real-time PCR. The16S rDNA copy numbers of amylolytic and lipolytic bacteria, such as Succinivibrio dextrinosolvens, Ruminobacter amylophilus and Anaerovibrio lipolytica, attached to corn kernels were increased for processed corn silage (P < 0.05), in particular at 2 h after the start of incubation. In addition, corn stemattached cellulolytic and hemicellulolytic bacteria, such as Fibrobacter succinogenes, ruminococci and Eubacterium ruminantium, increased in 16S rDNA copy numbers for processed corn silage (P < 0.05). This was observed for the initial incubation period from 10 min to 2 h. These results demonstrate more rapid attachment and heavier colonization of rumen bacteria to the processed compared with the unprocessed silage, which facilitates ruminal digestion and fermentation.Key words: Corn silage, mechanical processing, rumen fermentation, bacteria, attachment Kozakai, K., Nakamura, T., Kobayashi, Y., Tanigawa, T., Osaka, I., Kawamoto, S. et Hara, S. 2007. Incidence du conditionnement mécanique sur la fermentation in vitro de l'ensilage de maïs dans le rumen ainsi que sur sa colonisation par les bactéries et la dégradation de la matière sèche in situ. Can. J. Anim. Sci. 87: 259-267. Les auteurs ont étudié la fermentation de l'ensilage de maïs conditionné mécaniquement et sa colonisation par les bactéries du rumen dans le cadre d'une série d'expéri-ences in situ et in vitro en recourant à des vaches canulées au rumen. Les données issues des cultures continues simulant le rumen (Rusitec) montrent que le conditionnement de l'ensilage augmente la concentration totale d'acides gras volatils (P < 0,001) tout en réduisant le pH (P < 0,001), sans modification de la concentration d'azote ammoniacal (P > 0,05). Le conditionnement mécanique accroît le taux de disparition in situ de la matière sèche et la quantité totale de matière sèche dégradée, respectivement pour les rafles et les grains de maïs (P < 0,05). In situ, il améliore aussi la fixation initiale des bactéries du rumen responsables de la digestion du maïs, telle que suivie par PCR en temps réel. On note une hausse du nombre de copies de l'ADNr 16S des bactéries amylolytiques et lipolytiques comme Succinivibrio dextrinos...

Four tropical and four temperate grasses were subjected to nylon bag fiber degradation study with fistulated Holstein cattle as well as in vitro digestion with broad spectrum cellulase, and the degradability of cell wall carbohydrate and lignin for the respective forage grasses were determined. The degradability of neutral detergent fiber and acid detergent fiber for the same plant materials appeared to be similar, but that of acid detergent lignin was constantly lower. As for the plant materials used in the present study, Italian ryegrass, orchardgrass and guineagrass showed high degradability of fibers in nylon bag incubation, while setaria, cogongrass and wheat showed smaller degradability. In both nylon bag incubation and in vitro digestion experiments, the forage samples showing relatively lower degradability exhibited notably lower disappearance of xylose than that of glucose or arabinose. It was also observed that dry matter degradability correlated negatively with the initial content of esterified and/or etherified p-coumaric acid. These results were assumed to be caused by the difference in resistance towards rumen microbial degradation due to the concentration of lignin-carbohydrate complex. Es, ester-bonded; Et, ether-bonded; Es & Et, esterified and/or etherified; FA, ferulic acid; PCA, p-coumaric acid. 202 N. KASUYA et al. rumen degradability of dry matter (%) = a + b ¥ c Ϭ (c + r), where a, b and c are soluble fraction, potentially degradable fraction and rate, respectively, and r is a passage rate constant (0.02/h). ab , means in the same row that do not have a common superscript differ (P < 0.05).204 N. KASUYA et al.

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