I n 1992 it was estimated that 30 x 10l2 g more methane was emitted into the atmosphere than was removed, with animals being considered the largest single anthropogenic source. Ruminants produce 97% of the methane generated in enteric fermentation by animals. Estimates for methane emissions from animal wastes vary between 6 and 31% of that produced directly by the animal, with the most likely value being between 5 and 10% globally. Although rnethanogenic bacteria can improve the ejjicienq of fermentation preventing the accumulation of reducing ruminal hydrogen, alternutive means of channelling hydrogen and electrons are possible. Methane inhibitors can reduce methane emissions to zero in the short term but due to microbial adaptation the effects of these compounds are quickly neutralized and feed intake is often depressed. Methane emissions can be reduced by about 18% through the use of ionophores in the short term but there are indications that methanogens as well as other members of the microbial population can adapt to their presence. Defaunation reduces methane production by 20 to 50% depending upon diet. Although

. 1998. Intake, digestibility, methane and heat production in bison, wapiti and white-tailed deer. Can. J. Anim. Sci. 78: 681-691. A 3 × 2 factorial experiment was conducted in which the digestibility of alfalfa pellets and methane and heat productions were measured in bison, wapiti and white-tailed deer in February/March 1995 and in April/May 1995. Voluntary dry matter intake (DMI) while animals were individually fed averaged 70, 87 and 68 g kg -0.75 d -1 , respectively (P = 0.05), and was generally higher in April/May than in February/March. Corresponding organic digestibilities were 52.9, 54.1 and 49.1% (P = 0.10). There was also a trend (P < 0.1) for fiber digestibilities to be lowest for deer. Methane production (L kg -1 DMI), was 30.1, 23.5, and 15.0 L kg -1 for bison, wapiti and deer, respectively (P = 0.01), with more (P < 0.01) methane being produced in February/March than in April/May (28 vs. 18 L kg -1 DMI). No differences in heat production (kJ kg -0.75 ) or estimated energy requirements for maintenance could be detected between species, although animals numerically produced 40% more heat (881 vs. 632 kJ kg -0.75 , P = 0.13) in April/May when feed intakes were higher than in February/March. It was concluded that DMI of native ungulates is higher in spring than winter and that methane emissions per unit feed consumed were the highest with bison and the least with white-tailed deer. Il était généralement plus abondant en avril-mai qu'en février-mars. Les taux correspondants de digestibilité de la matière organique étaient de 52,9, 54,1 et 49,1 % (P = 0,10). La digestibilité des fibres était en général plus basse (P < 0,10) chez le cerf de Virginie. La production de méthane (L kg -1 IMS) était, respectivement, de 30,1, 23,5 et 15,0 pour le bison, le wapiti et le cerf de Virginie (P = 0,01) et elle était plus importante (P < 0,01) dans la période février-mars que dans les deux mois suivants, soit 28 contre 18. On ne relevait aucune différence entre les espèces pour ce qui est de la thermogenèse (kJ kg -0,75 ) ou des besoins énergétiques d'entretien calculés, mais les bêtes produisaient 40 % plus de chaleur (881 contre 632 kJ kg -0,75 , P = 0,13) en avril-mai, la prise alimentaire étant plus abondante qu'en février-mars. Il appert donc que l'ingéré de matière sèche des ongulés sauvages est plus important au printemps qu'en hiver et que les émissions de méthane par unité fourragère consommée étaient au niveau le plus élevé chez le bison et au niveau le plus bas chez le cerf de Virginie.

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