-The aim of this paper is to review the role of methane in the global warming scenario and to examine the contribution to atmospheric methane made by enteric fermentation, mainly by ruminants. Agricultural emissions of methane in the EU-15 have recently been estimated at 10.2 million tonnes per year and represent the greatest source. Of these, approximately two-thirds come from enteric fermentation and one-third from livestock manure. Fermentation of feeds in the rumen is the largest source of methane from enteric fermentation and this paper considers in detail the reasons for, and the consequences of, the fact that the molar percentage of the different volatile fatty acids produced during fermentation influences the production of methane in the rumen. Acetate and butyrate promote methane production while propionate formation can be considered as a competitive pathway for hydrogen use in the rumen. The many alternative approaches to reducing methane are considered, both in terms of reduction per animal and reduction per unit of animal product. It was concluded that the most promising areas for future research for reducing methanogenesis are the development of new products/delivery systems for anti-methanogenic compounds or alternative electron acceptors in the rumen and reduction in protozoal numbers in the rumen. It is also stressed that the reason ruminants are so important to mankind is that much of the world's biomass is rich in fibre. They can convert this into high quality protein sources (i.e. meat and milk) for human consumption and this will need to be balanced against the concomitant production of methane. methane / ruminants / global warning / reduction strategies Résumé -Production de méthane par les ruminants : sa contribution au réchauffement de la planète. Cet article examine le rôle du méthane dans le processus de réchauffement de la planète et évalue la contribution au méthane atmosphérique des gaz d'origine digestive issus principalement des ruminants. Les émissions annuelles de méthane d'origine agricole dans l'Europe des quinze ont été estimées récemment à 10,2 millions de tonnes et représentent la principale source des entrées Ann. Zootech. 49 (2000) 231-253 231 © INRA, EDP Sciences

This experiment studied the effect of 3 forms of presentation of linseed fatty acids (FA) on methane output using the sulfur hexafluoride tracer technique, total tract digestibility, and performance of dairy cows. Eight multiparous lactating Holstein cows (initial milk yield 23.4 +/- 2.2 kg/d) were assigned to 4 dietary treatments in a replicated 4 x 4 Latin square design: a control diet (C) consisting of corn silage (59%), grass hay (6%), and concentrate (35%) and the same diet with crude linseed (CLS), extruded linseed (ELS), or linseed oil (LSO) at the same FA level (5.7% of dietary DM). Each experimental period lasted 4 wk. All the forms of linseed FA significantly decreased daily CH(4) emissions (P < 0.001) but to different extents (-12% with CLS, -38% with ELS, -64% with LSO) compared with C. The same ranking among diets was observed for CH(4) output expressed as a percentage of energy intake (P < 0.001) or in grams per kilogram of OM intake (P < 0.001). Methane production per unit of digested NDF was similar for C, CLS, and ELS but was less for LSO (138 vs. 68 g/kg of digested NDF, respectively; P < 0.001). Measured as grams per kilogram of milk or fat-corrected milk yield, methane emission was similar for C and CLS and was less for ELS and LSO (P < 0.001), LSO being less than ELS (P < 0.01). Total tract NDF digestibility was significantly less (P < 0.001) for the 3 supplemented diets than for C (-6.8% on average; P < 0.001). Starch digestibility was similar for all diets (mean 93.5%). Compared with C, DMI was not modified with CLS (P > 0.05) but was decreased with ELS and LSO (-3.1 and -5.1 kg/d, respectively; P < 0.001). Milk yield and milk fat content were similar for LSO and ELS but less than for C and CLS (19.9 vs. 22.3 kg/d and 33.8 vs. 43.2 g/kg, on average, respectively; P < 0.01 and P < 0.001). Linseed FA offer a promising dietary means to depress ruminal methanogenesis. The form of presentation of linseed FA greatly influences methane output from dairy cows. The negative effects of linseed on milk production will need to be overcome if it is to be considered as a methane mitigation agent. Optimal conditions for the utilization of linseed FA in ruminant diets need to be determined before recommending its use for the dairy industry.

No abstract

No abstract

-Mycotoxins are secondary metabolites secreted by moulds, mostly belonging to the three genera Aspergillus, Penicillium and Fusarium. They are produced in cereal grains as well as forages before, during and after harvest, in various environmental conditions. Due to the diversity of their toxic effects and their synergetic properties, mycotoxins are considered as risky to the consumers of contaminated foods. Mycotoxin metabolism is complex and involves pathways of bioactivation and detoxification in both humans and animals. Detoxification occurs via biotransformation mediated by enzymes in the host cells and in the digestive microbial flora. Some of the toxins or their metabolites may become fixed in animal or human tissues. However, most are eliminated in the urine, faeces and milk. In animals, toxicity is generally revealed as chronic minor troubles and only rarely causes death. The presence of mycotoxins in feeds may decrease feed intake and affect animal performance. In addition, the possible presence of toxic residues in edible animal products (milk, meat, offal), may have some detrimental effects on human health. Maximum acceptable doses in feeds and milk have been set for certain mycotoxins by international authorities. The potential risks of mycotoxins may be controlled by checking plant material for fungal contamination, by improving methods of cultivation, harvest and storage, by eliminating or diluting toxins from the contaminated food or feeds, and by using adsorbents to reduce the bioavailability of toxins in the digestive tracts of animals. These measures will be assessed in the present paper. (0)4 73 63 46 59; e-mail: jouany@clermont.inra.fr présent dans le tube digestif. Certaines des toxines ou de leurs métabolites peuvent être fixés dans les tissus animaux ou humains. Cependant, la majorité est éliminée dans l'urine, dans les fèces et dans le lait. La toxicité se manifeste généralement sous forme de troubles chroniques difficiles à identifier, et rarement par la mort de l'animal. La présence de mycotoxines dans les aliments diminue la plupart du temps les quantités d'aliments ingérés ainsi que les performances zootechniques des animaux. La présence de résidus toxiques dans les produits animaux destinés à la consommation humaine (lait, viande, abats) constitue un risque potentiel qu'il est nécessaire d'évaluer pour mieux répondre à la demande sociétale de sécurité dans la chaîne alimentaire. Des doses acceptables devront être définies pour les toxines les plus dangereuses. En parallèle, des moyens de contrôle devront être mis en place pour vérifier l'innocuité des produits alimentaires mis sur le marché. Le risque potentiel des mycotoxines peut être diminué en évitant la contamination des plantes par les moisissures au moment de leur culture, de leur récolte et de leur conservation. Il est également possible de réduire la concentration en toxines des plantes contaminées par dilution avec des aliments sains et par des traitements appropriés, et (ou) de limiter la biodisponibilité des myc...