. 2004. Mitigation strategies to reduce enteric methane emissions from dairy cows: Update review. Can. J. Anim. Sci. 84: 319-335. Enteric methane (CH 4 ) emission is a major contributor to Canadian greenhouse gas emissions, and also a loss of feed energy during production. The objective of this paper is to provide an update on current management practices and new dietary strategies recently proposed to reduce CH 4 emissions from ruminants. Existing mitigation strategies for dairy, e.g., the addition of ionophores, fats, use of high-quality forages, and increased use of grains, have been well researched and applied. These nutritional changes reduce CH 4 emissions by manipulating ruminal fermentation, directly inhibiting methanogens and protozoa, or by diverting hydrogen ions away from methanogens. Current literature has identified new CH 4 mitigation options. These include the addition of probiotics, acetogens, bacteriocins, archaeal viruses, organic acids, plant extracts (e.g., essential oils) to the diet, as well as immunization, and genetic selection of cows. These new strategies are promising, but more research is needed to validate these approaches and to assess in vivo their effectiveness in reducing CH 4 production by dairy cows. It is also important to evaluate CH 4 mitigation strategies in terms of the total greenhouse gas budget and to consider the cost associated with the various strategies. More basic understanding of the natural differences in digestion efficiencies among animals as well as a better knowledge of methanogens and their interaction with other organisms in the rumen would enable us to exploit the potential of some of the new CH 4 mitigation strategies for dairy cattle production. Key words: Enteric methane, dairy cattle, mitigationBoadi, D., Benchaar, C., Chiquette, J. et Massé, D. 2004. Stratégies visant à réduire les dégagements de méthane entérique des vaches laitières: bilan. Can. J. Anim. Sci. 84: 319-335. Le méthane (CH 4 ) d'origine entérique contribue dans une large mesure aux émissions canadiennes de gaz à effet de serre et entraîne une perte de l'énergie tirée des aliments durant la production. Le présent article fait le point sur les pratiques de zootechnie actuelles et sur les stratégies d'engraissement récemment proposées pour réduire les dégagements de CH 4 des ruminants. Les stratégies d'atténuation existantes (addition d'ionophores, matière grasse, utilisation de fourrages de grande qualité, plus grande utilisation de grains) ont fait l'objet de maintes recherches et sont désormais bien appliquées. Les changements nutritionnels qu'elles introduisent diminuent les émissions de CH 4 en modifiant la fermentation dans le rumen, en inhibant directement la production de méthanogènes et la population de protozoaires ainsi qu'en détournant les ions hydrogène des méthanogènes. La documentation scientifique mentionne de nouvelles méthodes pour atténuer la libération de CH 4 . Ces méthodes comprennent l'ajout de probiotiques, d'acétogènes, de bactériocine, de virus archaïques, d'aci...

. 2004. Effect of low and high forage diet on enteric and manure pack greenhouse gas emissions from a feedlot. Can. J. Anim. Sci. 84: [445][446][447][448][449][450][451][452][453]. The objectives of this study were to assess enteric methane (CH 4 ) production by beef steers fed one of two isocaloric diets with different forage:grain ratios and to quantify greenhouse gas (GHG) emissions from bedded manure packs in the eight feedlot pens holding these steers (14 head pen -1 ). Five animals (252 ± 20 kg) in each pen were randomly selected for measurement of CH 4 emissions over the course of the 126-d feeding trial. Two 24-h gas collections were completed for each steer in each of three collection periods using the sulfur hexafluoride tracer gas technique. The fluxes of nitrous oxide (N 2 O), methane (CH 4 ) and carbon dioxide (CO 2 ) from bedding packs were measured using vented static chambers in each sampling period. Methane production (L d -1 ) was 42% higher (P < 0.05) from steers fed the low forage:grain ratio than from steers fed the high forage:grain ratio. Overall, methane production (% of gross energy intake) ranged from 0.9 to 6.9% on the low forage:grain diet and from 0.7 to 4.9% on the high forage:grain diet. Daily CH 4 emissions were similar in the first two periods and increased during the third sampling period. There was no effect of diet on manure pack temperature during sampling, however, the manure pack was deeper (P < 0.05) in pens holding animals fed the high forage:grain diet. Furthermore, diet had no effect on the manure pack fluxes. Total daily non-CO 2 emissions from enteric and manure pack sources (CO 2 equivalent) were different (P < 0.05) between dietary treatments and averaged 1931 ± 81 g head -1 d -1 for the low forage:grain and 1394 ± 81 g head -1 d -1 for the high forage:grain diet. . L'étude devait servir à évaluer la production entérique de méthane (CH 4 ) par des bouvillons de boucherie recevant deux rations isocaloriques à rapport fourrage:grain différent ainsi qu'à déterminer le volume de gaz à effet de serre (GES) libérés par la litière accumulée dans les huit enclos où les animaux étaient gardés (14 sujets par enclos). Cinq animaux (252 ± 20 kg) ont été choisis au hasard dans chaque enclos et on a mesuré leurs émissions de CH 4 au cours des 126 jours de l'expérience. Pour chaque bouvillon, on a recueilli les gaz pendant 24 heures à deux reprises dans chacune de trois périodes en utilisant de l'hexafluorure de soufre comme traceur. Les flux d'oxyde nitreux (N 2 O), de méthane (CH 4 ) et de dioxyde de carbone (CO 2 ) issus de la litière accumulée ont été mesurés au moyen de cellules aérées de manière statique durant chaque période d'échantillonnage. Les animaux nourris avec la ration à faible rapport fourrage:grain produisent 42 % plus (P < 0,05) de méthane (litres par jour) que ceux nourris avec l'autre ration. Dans l'ensemble, la production de méthane (pourcentage de la quantité d'énergie brute ingérée) varie de 0,9 à 6,9 % pour la ration à faible rapport fourrage:grain et de 0...

. 2002. Methane production from dairy and beef heifers fed forages differing in nutrient density using the sulphur hexafluoride (SF 6 ) tracer gas technique. Can. J. Anim. Sci. 82: [201][202][203][204][205][206]. The effects of cattle breed type [dairy (Holstein) versus beef (Charolais × Simmental)] and forage quality (high, medium and low) on methane production were measured under ad-libitum and restricted feeding conditions. The in vitro organic matter digestibility (IVOMD) of the forage diets was high = 61.5%, medium = 50.7% and low = 38.5%. Each hay diet was fed to four animals (two dairy and two beef heifers) in three periods of four 3 × 3 Latin squares. Each period consisted of 23 d during which heifers were individually fed their assigned forage for 14 d on ad-libitum feeding. Following this, intake was restricted to 2% of body weight (BW) for 9 d. Methane production was measured for five 24-h intervals in each period at both levels of intake using the SF 6 gas technique. Methane production was not different (P > 0.05) between dairy (238.0 ± 6.9 L d -1 ) and beef cattle (228.6 ± 7.8 L d -1 ) under either level of feeding. Forage quality affected CH 4 (L d -1 ) output, with high = medium > low during ad-libitum feeding. This effect of forage quality on CH 4 production was absent during restricted feeding (P > 0.05). Day-to-day variation in CH 4 production was 26.9 and 27.1% on ad-libitum and restricted feeding respectively (P < 0.05), whereas animal-to-animal variation (P < 0.05) was 26.6% (ad libitum) and 25.3% (restricted). On ad-libitum feeding, dry matter intake (DMI) was strongly correlated (P = 0.0001; r = 0.8) with CH 4 production (L d -1 ), and accounted for 64% of daily variation in CH 4 production. Methane [L kg -1 digestible organic matter intake (DOMI)] was highest (P < 0.05) on low-quality diets under both feeding regimes, and was not influenced (P > 0.05) by cattle type. Methane production as a percent of gross energy intake (GEI) was not influenced by diet. It can be concluded that the SF 6 tracer technique provides a measure of enteric CH 4 production directly from animals under production conditions. There were no differences in CH 4 production between dairy and beef breeds, but the quality of forages affected CH 4 production under both ad-libitum and restricted feeding. Les auteurs ont mesuré l'incidence du type de bovin [race laitière (Holstein) ou de boucherie (Charolais × Simmental)]et de la qualité du fourrage (haute, moyenne, faible) sur le volume de méthane produit par des génisses nourries à satiété ou rationnées. La digestibilité in vitro de la matière sèche organique correspondait à 61,5 % pour le fourrage de haute qualité, à 50,7 % pour celui de qualité moyenne et à 38,5 % pour celui de faible qualité. Chaque type de fourrage a été servi à quatre animaux (2 géniss-es laitières et 2 de boucherie) trois périodes durant, en quatre carrés latins 3 × 3. Chaque période comportait 23 jours durant lesquels les animaux ont chacun reçu le type de fourrage qui leur avait été attribué à sat...

. Validation of the sulphur hexafluoride (SF 6 ) tracer gas technique for measurement of methane and carbon dioxide production by cattle. Can. J. Anim. Sci. 82: 125-131. Methane (CH 4 ) and carbon dioxide (CO 2 ) production from six crossbred yearling beef heifers (400 ± 13.0 kg) were measured, using the sulphur hexafluoride (SF 6 ) tracer gas technique (Tracer) and open-circuit hood calorimetry (Cal) to validate the former in estimating rumen CH 4 and CO 2 production in the field. Animals were individually fed a diet consisting of 50% barley concentrate and 50% alfalfa cubes at 1.3 × maintenance requirements daily. Heifers were divided into two groups for individual animal 24-h gas measurements by each method. Each group of heifers was rotated between the Cal and Tracer techniques for 6 consecutive days in an incomplete block design. Methane production ranged from 108 to 145 L d -1 (mean 130 ± 4.0 L d -1 ) using the Cal technique, and 90 to 167 L d -1 (mean 137 ± 4.0 L d -1 ) using the Tracer technique. The mean CH 4 production (L d -1 ) was not different (P = 0.24) between the two methods. Carbon dioxide production with the Tracer technique was 20% higher than CO 2 production with the Cal technique (P < 0.01). The range of CO 2 production was 1574 to 2049 L d -1 (mean 1892 ± 74.0 L d -1 ) by Cal, and 1541 to 3330 L d -1 (mean 2353 ± 74.0 L d -1 ) by Tracer. Day-to-day variation in CH 4 production was not different within each method (P > 0.05); however, animal-to-animal variation (11.7%) was significant for the Tracer technique (P = 0.04), but not for the Cal technique (P = 0.53). Comparison of the equality of variance between the two methods showed that there were no differences in variations (P > 0.05) between Cal and Tracer for CH 4 production. On the other hand, variations in CO 2 production were not equal (P > 0.05) between methods. Day-to-day variation in CO 2 production was significant using Cal, but not Tracer (P > 0.05). Animal-to-animal variation in CO 2 production was 1.6 and 11.8% by Cal and Tracer techniques, respectively. It can be concluded that the SF 6 tracer technique accurately estimated rumen CH 4 production, but CO 2 production was 20% higher. The study suggests that for CH 4 measurements using the SF 6 tracer technique, more animal numbers are needed than for Cal to reduce animal-to-animal variation. . Le volume moyen de CH 4 (litres par jour) était identique (P = 0,24) dans les deux cas. La quantité de CO 2 obtenue par traçage dépassait celle établie par calorimétrie de 20 % (P < 0,01). La production de CO 2 variait de 1 574 à 2 049 litres par jour (moyenne de 1 892 ± 74,0 litres par jour) pour la technique calorimétrique et de 1 541 à 3 330 litres (moyenne de 2 353 ± 74,0 litres par jour) pour celle du traçage. La quantité de CH 4 libérée ne varie pas beaucoup d'un jour à l'autre, quelle que soit la méthode (P > 0,05). Toutefois, elle varie sensiblement d'un animal à l'autre (11,7 %) avec la technique du traçage (P = 0,04), mais pas avec la technique calorimétrique (P = 0,53). Quand on...

. 2006. Enteric methane emissions from backgrounded cattle consuming all-forage diets. Can. J. Anim. Sci. 86: 393-400. To quantify enteric methane (CH 4 ) emissions of growing cattle consuming allforage diets, a field study utilizing 144 British × Continental crossbred steers (262 ± 4 kg) was conducted during an 84-d overwintering period followed by a 56-d grazing period in one of two, grass-based pastures. Enteric CH 4 emissions were quantified using the sulphur hexaflouride (SF 6 ) tracer gas technique. During the overwintering period, four qualities of chopped alfalfa-grass silage, ranging in NDF content from 46.4 to 60.8%, DM basis, were utilized. Steers fed the lowest quality forage (60.8% NDF) had lower DMI, (6.8 ± 0.4 kg head -1 , P = 0.0075) and lower ADG (0.83 ± 0.03 kg d -1 , P = 0.0028) compared with those fed higher quality forage whose intake ranged from 8.2 to 9.1 ± 0.4 kg d -1 , with gains ranging from 1.00 to 1.06 ± 0.03 kg d -1 . Enteric emissions (% GE intake) were not influenced by forage quality across this range of NDF values; however, CH 4 losses did decrease from 6.8 to 4.7 ± 0.3% GE intake as the winter period progressed. Increased DMI, accompanied by a decrease in the proportion of feed energy lost as enteric CH 4 emissions, suggests that utilization of the lower-quality forage improved as steers reached higher body weights. Emissions were influenced by pasture quality and availability, as highest CH 4 emissions (11.3% GE intake, P = 0.0005) were observed when quality was low and DM availability was limited (738 kg ha -1 ). This study demonstrates that growing cattle consuming all-forage diets typical of those utilized in Western Canada during the winter feeding period will lose 5.1 to 5.9% of feed energy as CH 4 . Further, it has shown that emissions from growing cattle on grass-based pastures may exceed 10% GE intake -a value that is greater than those previously reported for growing cattle grazing legume-based pastures. (SF 6 ). Pendant l'hivernage, les animaux ont reçu de l'ensilage haché de graminées et de luzerne de quatre qualités différentes, dont la concentration en fibres au détergent neutre (FDN) variait de 46,4 à 60,8 %, selon la teneur en matière sèche. Les bouvillons nourris avec l'ensilage de la plus piètre qualité (60,8 % de FDN) ingèrent moins de matière sèche (6,8 ± 0,4 kg par jour, P = 0,0075) et gagnent quotidiennement moins de poids en moyenne (0,83 ± 0,03 kg par jour, P = 0,0028) que ceux engraissés avec le fourrage de meilleure qualité, qui ingèrent 8,2 à 9,1 ± 0,4 kg de matière sèche par jour et gagnent 1,00 à 1,06 ± 0,03 kg de poids quotidiennement. Les émissions entériques (pourcentage de l'énergie brute absorbée) ne varient pas avec la qualité du fourrage pour cette fourchette de valeurs des FDN, mais les pertes de CH 4 baissent de 6,8 à 4,7 ± 0,3 % de la quantité d'énergie brute absorbée à mesure que l'hiver progresse. La hausse de l'ingestion de matière sèche et la baisse de la proportion de l'énergie alimentaire perdue dans les émissions entériques de CH 4...