Canada is committed to reducing its greenhouse gas emissions to 6% below 1990 amounts between 2008 and 2012, and methane is one of several greenhouse gases being targeted for reduction. Methane production from ruminants is one area in which the agriculture sector can contribute to reducing our global impact. Through mathematical modeling, we can further our understanding of factors that control methane production, improve national or global greenhouse gas inventories, and investigate mitigation strategies to reduce overall emissions. The purpose of this study was to compile an extensive database of methane production values measured on beef cattle, and to generate linear and nonlinear equations to predict methane production from variables that describe the diet. Extant methane prediction equations were also evaluated. The linear equation developed with the smallest root mean square prediction error (RMSPE, % observed mean) and residual variance (RV) was Eq. I: CH(4), MJ/d=2.72 (+/-0.543) + [0.0937 (+/-0.0117) x ME intake, MJ/d] + [4.31 (+/-0.215) x Cellulose, kg/d] - [6.49 (+/-0.800) x Hemicellulose, kg/d] - [7.44 (+/-0.521) x Fat, kg/d] [RMSPE=26.9%, with 94% of mean square prediction error (MSPE) being random error; RV=1.13]. Equations based on ratios of one diet variable to another were also generated, and Eq. P, CH(4), MJ/d=2.50 (+/-0.649) - [0.367 (+/-0.0191) x (Starch:ADF)] + [0.766 (+/-0.116) x DMI, kg/d], resulted in the smallest RMSPE values among these equations (RMSPE=28.6%, with 93.6% of MSPE from random error; RV=1.35). Among the nonlinear equations developed, Eq. W, CH(4), MJ/d=10.8 (+/-1.45) x (1-e([-0.141 (+/-0.0381) x DMI, kg/d])), performed well (RMSPE=29.0%, with 93.6% of MSPE from random error; RV=3.06), as did Eq. W(3), CH(4), MJ/d=10.8 (+/-1.45) x [1-e({-[-0.034 x (NFC/NDF)+0.228] x DMI, kg/d})] (RMSPE=28.0%, with 95% of MSPE from random error). Extant equations from a previous publication by the authors performed comparably with, if not better than in some cases, the newly developed equations. Equation selection by users should be based on RV and RMSPE analysis, input variables available to the user, and the diet fed, because the equation selected must account for divergence from a "normal" diet (e.g., high-concentrate diets, high-fat diets).

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CunrsropuensoN, R. J. exo KENNeov

R. J. l9'/6. Effects of cold on digestibility, retention time of digesta, reticulum motility and thyroid hormones in sheep. Can. J. Anim. In the first of two experiments, l2 closely shorn yearling wethers received grass hay either in the long lbrm or pelletcd form and wcre acclimated b temperatures of 0. warm treatments, respectively. The corresponding respective wet-bulb temperatures were 0.4 + L9. 7.1 + 1.7 and 9.9 + 2.5 C. Each temperature exposure consisted of a 27-tct 3l-day acclimation period, followed by a l0-day digestibility measurement period.All sheep were shorn to a fleece depth of 4-6 mm, 7 or 8 days before and I day after each digestibility period.Daily total fecal outputs were collected at about 1700 h during the digestibility trials. Feces were mixed and weighed; 5% of the wet material was stored at -10 C. Aliquots (5c/c vlv) of each urine collection were also retained and stored at -I 0 C. The dry matter content of samples of the Table l The dry matter (DM), gross energy (E), acid-detergent fiber (ADF) and crude protein (CP) content of the long hay and pelleted hay

. 1992. Effect of prolonged thermal exposure on heat production, reticular motility, fumen-fluid and -particulate passage-rate constants, and apparent digestibility in steers. Can. J. Anim. . Six steers fitted with permanent rumen cannulae and fed alfalfa-grass hay were kept at either -10, l0 or 28"C for 21 d to evaluate the effects ofprolonged thermal exposue on heat production (HP) and digestive responses. HP was lowest at 28'C and increased significantiy (P < 0.05) as the ternperature was reduced to -10'C. The duration of the biphasic reticular contraction during resting was significantly (P < 0.05) reduced at -10'C (5.4 s) compared with that at 10"C (5.7 s) and 28"C (5.7 s) whereas duration and amplitude of biphasic reticular contractions during rumination were elevated at -10'C (P < 0.05). Apparent digestibilities of dry matter, orga4c matter, neutral detergent fibre and crude protein on average were 17% (range 9-16%) higher (P < 0'05) at 28 than at 10'C. The particulate passage-rate constant was higher at -10"C (P < 0.05) than at 10 and 28"C (0.046 vs. 0.038 and 0.034, respectively). The fluid passage-rate constant showed a quadratic response to temperature and was inversely related to digestibility. This study suggests prolong6e ir un regime thermique sur la production calorifique et sur la digestion. La production calorifique 6tait au plus bas d 28"C et augmentait significativement (P < 005) ir mesure que les temperatures descendaient jusqu'd -10"C. La dur6e de la contraction r6ticulaire biphas6e au repos 6tait significativement (P < 005) raccourcie d -10"C (5,4 s) par rapport )r 10 et d 28'C (5,7 s), mais durant la rumination elle 6tait significativement plus 6lev6e (P < 0,05) ir -10"C. La digestibilit6 apparente de la matidre sdche, de la matidre organique, des fibres au d6tergent neutre et des prot6ines brutes 6tait en moyenne ll% (6,cart 9{6) plus forle (P < 0,05) ir 28'C qu'h 10'C. La constante de transit des particules solides (par heure) 6tait plus haute d -10'C (P < 0,05) qu'd 10 et 28"C (0,046 contre 0038 et 0,034 respectivement). La constante de transit des liquides montrait une r6ponse quadratique ir la temp6rature et 6tait inversement reli6e ir la digestibilit6. L6tude porte d penser que les temp6ratures d'ambiance influent non seulement sur la cin6tique des matibres solides et des liquides mais 6galement sur la forme et sur la p6riodicit6 des contractions r6ticulaires. En outre, les modihcations thermo-induites de la dur6e et de l'amplitude des contractions r6ticulaires durant la rumination, par rapport d la phase, de repos 6taient associ6es ir des modifications des constantes du taux de transit des matibres solides.

Ekpe, E. D. and Christopherson, R. J. 2000. Metabolic and endocrine responses to cold and feed restriction in ruminants. Can. J. Anim. Sci. 80: 87-95. Twenty-four wether lambs were assigned to different temperature and feeding levels to assess their metabolic and endocrine profiles and to test the hypothesis that energy conservation responses of sheep to feed restriction occur in warm but not cold environments. Lambs were kept in warm (W; 23 ± 2°C) or cold (C; 0 ± 2°C) environments and received either an ad libitum (A) or a restricted (1.35 × maintenance) (R) level of feed intake, thus creating four treatment groups (WA, WR, CA and CR). Average daily gain (ADG), feed intake, metabolic rates, rectal temperature, and plasma levels of insulin, thyroxine (T4), triiodothyronine (T3) and cortisol were recorded during three periods of 5 wk each. The ADG was lower (P < 0.001) in feed-restricted groups. Cold exposure reduced the ADG along with feed efficiency in the first period (P < 0.01). Metabolic rate was lowered by feed restriction (P < 0.01) in periods 1 and 3, but was increased by cold exposure in ad libitum-fed sheep during period 1 (P < 0.05). Both cold exposure and feed restriction lowered rectal temperature (P< 0.001). Plasma insulin concentration was lowered by feed restriction (P < 0.05) and was increased (P < 0.05) by cold exposure during periods 2 and 3. Plasma T3 concentration was reduced (P < 0.05) by feed restriction and was increased by cold exposure during periods 1 and 2. Plasma T4 level remained unaltered (P > 0.05) while plasma cortisol concentration was increased by both cold exposure and feed restriction (P < 0.01). The results indicate that lambs show metabolic and physiological responses to feed restriction, which conserve energy in a cold as well as a warm environment. Le gain quotidien moyen, l'ingéré alimentaire, les taux de thermogenèse, la tempéra-ture rectale et les niveaux plasmatiques d'insuline, de thyroxine (T4), de triiodothyronine (T3) et de cortisol étaient mesurés durant trois périodes de cinq semaines chacune. Le GQM était plus faible (P < 0,001) parmi les groupes rationnés. L'exposition au froid abaissait le GQM et l'efficacité alimentaire dans la première période seulement (P < 0,01). Le taux métabolique énergétique était diminué (P < 0,01) par le rationnement dans les périodes 1 et 3, mais était augmenté par l'exposition au froid des moutons nourris à satiété durant la première période (P < 0,05). Exposition au froid et alimentation restreinte provoquaient toutes deux une chute de la température rectale (P < 0,001). Les concentrations plasmatiques d'insuline et de T3 étaient abaissées (P < 0,05) par suite du rationnement, mais augmentées (P < 0,05) en ambiance froide durant les périodes 2 et 3 dans le cas de l'insuline et 1 et 2 dans celui de la T3. Les niveaux plasmatiques de T4 demeuraient inchangés (P > 0,05), tandis que ceux de cortisol augmentaient en réponse à l'exposition au froid et au rationnement (P < 0,01). Il ressort de ces observations que, exposés à une alimentat...

A respiratory pattern analyzer for livestock is described. Continuous measurements can be made of oxygen consumption and respiratory output of carbon dioxide, methane and carbon-14, from which rates of heat production can be estimated by indirect calorimetry. The apparatus was designed on the basis of four modules (respiratory gas collection; gas flow and monitoring; gas sampling and analyses; recording) which can be operated independently or as integrated systems. The module components are duplicated in different forms to permit flexibility and ease of operation in studies on livestock subject to various thermal environments and experimental situations.

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