Quantitative effects of alfalfa extract supply on rice straw degradation, fermentation and biomass synthesis by rumen microorganisms in vitro

International audienceIn Asia and Africa, rice straw enters into livestock feeds as the main constituent. It is sometimes associated with fresh legume material, from local garden farming or from legume-cereal rotations, but the possible benefits of this practice need to be estimated more precisely, with special attention to the influence of cytoplasmic contents other than nitrogen or macrominerals on rumen microbial metabolism. In the present study, fresh Medicago sativa extract (AE) was chosen as a model of cytoplasmic contents from tops of tropical legumes such as Vigna unguiculata. It was obtained from whole plants harvested at the beginning of flowering (primary growth). The effects of AE supplementation on a rumen microbial community maintained on a diet made of rice straw and inorganic nitrogen (CP: 73.3 g$\cdot$kg$^{-1}$ DM) were assessed in dual outflow continuous culture. Three input levels were applied in order to detect curvilinear effects: 0, 0.227 and 0.455 ml$\cdot$g$^{-1}$ straw DM. The pH and the redox potential varied from 6.72 to 6.84, and from -335 to -370 mv respectively. The addition of AE had minor effects on fermentation variates. The true degradability of dietary OM and the degradabilities of ash-free NDF and ADF were not modified by AE. Alfalfa extract lowered the outflow of fermented OM (FOM) by 14% while it enhanced the microbial OM outflow (+33%) and the efficiency of microbial protein synthesis (15 to 26 g N$\cdot$kg$^{-1}$ FOM). This effect was curvilinear, and appeared negligible above 45-50% of the maximal extract input rate. This legitimised the addition of fresh legume materials to the diet even in small amounts.Les effets quantitatifs de l'apport d'extrait de luzerne sur la dégradation de la paille de riz, la fermentation et la synthèse de biomasse par les micro-organismes du rumen in vitro. En Asie et en Afrique, l'affouragement des ruminants en paille de riz est parfois associé à des déchets de maraîchage ou à des légumineuses (Niébé). Les bénéfices éventuels de cette pratique doivent être vérifiés, en portant une attention particulière à l'action des composés cytoplasmiques autres que les protéines et les minéraux majeurs sur le métabolisme des micro-organismes du rumen. Le contenu cytoplasmique du modèle choisi est un extrait par pressage d'une luzerne (Medicago sativa) récoltée en début de floraison (EL). Nous avons étudié l'effet de l'EL sur une communauté de micro-organismes du rumen maintenue en fermenteurs à double effluent sur une ration paille de riz + azote inorganique (MAT : 73.3 g$\cdot$kg$^{-1}$ MS). Trois niveaux d'apport ont été appliqués pour détecter d'éventuels effets curvilinéaires : 0 ; 0,227 ; 0,455 ml$\cdot$g$^{-1}$ MS paille. Le pH et le potentiel redox ont varié de 6,72 à 6,84, et de -335 à -370 mv respectivement. L'EL n'a pas significativement modifié les variables fermentaires, ni la dégradabilité réelle de la MO, ou les dégradabilités du NDF et ADF déminéralisés. L'extrait de luzerne a diminué le flux de MO fermentée (MOF) de 14 % tandis qu'il a accru le flux de MO microbienne (+ 33 %) et l'efficacité de la synthèse de protéines microbiennes (de 15 à 26 g N$\cdot$kg$^{-1}$ MOF). Cet effet a été curvilinéaire et paraît négligeable au delà de 45-50 % du niveau d'apport maximal. Dans notre essai, l'EL n'a pas significativement modifié l'apport d'énergie et d'azote aux micro-organismes. Son action catalytique sur le métabolisme microbien justifie l'apport de matière végétale fraîche dans la ration même en faible quantité

Isolation and expeditious morphological, biochemical and kinetic characterization of propolis-tolerant ruminal bacteria Isolamento e caracterização expedita morfológica, bioquímica e cinética de bactérias ruminais tolerantes a própolis

It was aimed in this work to evaluate bacterial strains tolerant to products based on propolis (LLOS) through the isolation, morphological and biochemical characterization techniques in diets with roughage:concentrate ratio 100:0 and 50:50. For roughage diets, the products LLOSC1 and LLOSB3 were evaluated, and for 50:50% diets, the products LLOSC1, LLOSD1, LLOSA2, and LLOSC3, which differed in alcoholic concentrations (1, 2 and 3) and propolis (A, B, C and D) concentrations. The ruminal liquid was anaerobically incubated at 39°C for 6 days in medium containing LLOS. After isolation, the strains were submitted to Gram staining and the bacterial growth was monitored by photospectrometer. It was evaluated the strain growth in the presence of the following subtracts: arabinose, cellulose, glucose, cellobiose, xylose, fructose, and lactose. In roughage diets, strains tolerant to LLOSC1 and LLOSB3 were similar to carbohydrates degradation, except lactose in which LLOSC1 was superior to strains tolerant to LLOSB3. For diets with 50:50 roughage:concentrate ratio, the products LLOSC3 and LLOSA2 stood out because they selected the highest number of strains able to degrade most of the tested carbohydrates. The results suggest that tolerance to propolis is higher in Gram-positive strains with several growth metabolic levels.<br>Objetivou-se avaliar cepas bacterianas tolerantes a produtos à base de própolis pelas técnicas de isolamento, caracterização morfológica e bioquímica, em dietas com relação volumoso: concentrado de 100:0 e 50:50. Para dietas volumosas foram avaliados os produtos LLOSC1 e LLOSB3 e, para dietas 50:50% os produtos LLOSC1, LLOSD1, LLOSA2 e LLOSC3, diferentes quanto aos teores alcoólicos (1, 2 e 3) e as concentrações de própolis (A, B, C e D). O líquido ruminal foi incubado anaerobiamente a 39°C durante 6 dias em meio contendo LLOS. Após o isolamento, as cepas foram submetidas à coloração de Gram e o crescimento bacteriano foi monitorado por espectrofotômetro. Foi avaliado o crescimento das cepas na presença dos substratos: arabinose, celulose, glicose, celobiose, xilose, frutose e lactose. Em dietas volumosas as cepas tolerantes a LLOSC1 e LLOSB3 foram semelhantes na degradação dos carboidratos, exceto lactose no qual LLOSC1 foi superior às cepas tolerantes a LLOSB3. Para dieta 50:50 de volumoso:concentrado, destacaram-se os produtos LLOSC3 e LLOSA2, que selecionaram maior número de cepas capazes de degradar a maioria dos carboidratos testados. Os resultados sugerem que a tolerância à própolis foi maior nas cepas Gram-positivas, com níveis metabólicos de crescimento diversos