During the last decades, considerable research on methane production in the rumen and its inhibition has been carried out. Initially, as methane production represents a significant loss of gross energy in the feed (2–15%), the ultimate goal of such intervention in rumen fermentation was an increase in feed efficiency. A second reason favouring research on methane inhibition is its role in the global warming phenomenon and in the destruction of the ozone layer. In this review, the authors describe briefly several interventions for reducing methane emission by ruminants. The objective can be reached by intervention at the dietary level by ration manipulation (composition, feeding level) or by the use of additives or supplements. Examples of additives are polyhalogenated compounds, ionophores and other antibiotics. Supplementation of the ration with lipids also lowered methanogenesis. More biotechnological interventions, e.g., defaunation, probiotics and introduction of reductive acetogenesis in the rumen, are also mentioned. It can be concluded that drastic inhibition of methane production is not unequivocally successful as a result of several factors, such as: instantaneous inhibition often followed by restoration of methanogenesis due to adaptation of the microbes or degradation of the additive, toxicity for the host animal, negative effects on overall digestion and productive performance. Therefore, methanogenesis and its inhibition cannot be considered as a separate part of rumen fermentation and its consequences on the animal should be taken into account.

Control of rumen methanogenesis.

Different methods of optimizing feed conversion into nutrients in the rumen are now available to scientists. But the rumen must be considered as an integrated system and this makes it difficult to rationalize manipulation. The observed result of any treatment is a combination of several interactive reactions. Any change to one component of the system has several uncontrolled effects on other components. The positive effects aimed for are sometimes associated with undesirable effects. Numerous chemical additives have been studied during the last two decades among which ionophore antibiotics represent the most important group. The interest of non-ionophore antibiotics, methane inhibitors, and compounds inhibiting proteases or deaminases, has also been considered during the last years. The observed effects of these chemical additives on animals, and their possible mode of action on rumen microbes and on animal metabolism, are discussed. However, the risks of the presence of residues in meat and milk are questioned by consumers. Microbial activity in the rumen can be altered by feeding animals with large amounts of certain food constituents (fats, starch) or minerals (buffer substances). The responses in the rumen to these dietary conditions are analyzed in terms of the digestive effects on plant cell wall degradation and microbial protein synthesis. Modification of the rumen microbial population is now considered as a possible approach to rumen manipulation by scientists. The effects on digestion of the elimination of ciliate protozoa (defaunation) are presented. The feasibility of these objectives, from a practical standpoint, is discussed. Finally, there is an overview of the effects of the addition of live yeasts (Saccharomyces cerevisciae), or fungi (Aspergillus orizae), used as probiotics. A possible mode of action of probiotics on the rumen ecosystem is suggested.

Manipulation of microbial activity in the rumen

Effects of the ionophore antibiotics lasalocid and cationomycin on ruminal fermentation in vitro (RUSITEC)

A study of the toxicity of epinigericin, an antibiotic ionophor, towards the ciliate Tetrahymena pyriformis showed that this molecule stopped cell division, increased cell volume and led to a more basic intracellular pH. The action of epinigericin was probably linked to its function as an ionophor. The ionic selectivity of this molecule is still not known. The raising of the intracellular pH of ciliates by this antibiotic may be linked to its toxic action and its ion-transport mechanism in Tetrahymena. *** DIRECT SUPPORT *** AG903066 00009

Epinigericin toxicity towards Tetrahymena pyriformis GL; changes in cell volume and intracellular pH

The antimicrobial and immunomodulatory effects of Ionophores for the treatment of human infection

The decrease in methanogenesis observed in the presence of monensin was also found with cationomycin and lysocellin. With the exception of lysocellin, which greatly reduced protein degradation of peanut meal, and of nigericin, which had no effect on this parameter, the 2 other molecules presented the same action as monensin. The negative effect of monensin on microbial ammonia uptake was demonstrated with the same intensity in the presence of cationomycin; it was slightly higher with nigericin and particularly accentuated with lonomycin and lysocellin. Three ester derivatives of monensin (monensin acetate, monensin propionate and monensin butyrate) had a similar action to that of monensin on the orientation of rumen fermentations. The monensin isobutyrate derivative appeared to be more active than monensin and only weakly altered microbial ammonia uptake. The oxolonomycin and hydroxolonomycin derivatives behaved identically to lonomycin with respect to microbial metabolism and protein nitrogen degradation. Unlike the molecules from which they derive, the deacylated cationomycin and nigericic acid had no effect on the orientation of rumen fermentations. Of the compounds tested and presenting a potential ’growthpromoting action’ at least comparable to that of monensin, and which demonstrated lower toxicity on mice, three molecules (oxolonomycin, lysocellin and cationomycin) appeared to present a zootechnical interest as feed additives for growing cattle.

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M.-C. Hillaire

Papers

In vitro study of the effect of different ionophore antibiotics and of certain derivatives on rumen fermentation and on protein nitrogen degradation.