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ANIMAL NUTRITION |
Agriculture and Agri-Food Canada, Research Centre, Lethbridge, Alberta, Canada
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Abstract |
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 Top Abstract IntroductionExperimental ProceduresResultsDiscussionImplicationsLiterature Cited |
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Key Words: Barley • Beef Cattle • Carbon Dioxide • Corn • Greenhouse Gases • Methane
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Introduction |
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TopAbstractIntroductionExperimental ProceduresResultsDiscussionImplicationsLiterature Cited |
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). Methane is a potent greenhouse gas and its release into the atmosphere is directly linked with animal agriculture, particularly ruminant production. Methane emissions result during microbial fermentation of feed within the rumen and represent a loss in productive energy for the animal. There is a need to understand the factors affecting variability in enteric CH4 production to decrease the uncertainty in greenhouse gas emission inventories and to identify viable greenhouse gas reduction strategies.
Energy lost as enteric CH4 from mature cattle ranges from 2 to nearly 12% of GE intake (Johnson et al., 2000). The range in emissions is due mainly to the level of feed intake and the composition of the diet (Johnson and Johnson, 1995; Moss et al., 2000; Benchaar et al., 2001). For beef cattle, intensive feedlot systems result in less CH4 per unit of meat produced compared with extensive grazing systems due to faster growth rate and shorter time to market (Clemens and Ahlgrimm, 2001). The Intergovernmental Panel on Climate Change (IPCC, Tier 2) estimated that feedlot cattle lose 3.5% of GE intake as CH4 (Houghton et al., 1996). This estimate was derived from cattle consuming high-grain diets containing mainly corn grain, as CH4 emissions for barley grain diets have not been extensively evaluated. Johnson et al. (2000) speculated that high-grain barley diets result in greater CH4 emissions than would be expected from high-grain corn diets, based on CH4 losses of 6.5 to 12% of GE reported previously for barley diets (Hashizume et al., 1968; Whitelaw et al., 1984).
The objective of this experiment was to determine the CH4 emissions from feedlot cattle fed backgrounding and finishing diets containing corn or barley grain.
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Experimental Procedures |
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TopAbstractIntroductionExperimental ProceduresResultsDiscussionImplicationsLiterature Cited |
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Experimental Design and Animals
The experiment was designed as a randomized complete block design with two treatments, barley and corn. Eight cattle were allocated to each of two blocks, with four cattle in each block individually fed either treatment. The experiment consisted of a 42-d backgrounding phase and a 32-d finishing phase, separated by a 35-d transition period.
The 16 Angus heifers used had been given an ear tag, vaccinated with a modified live vaccine for infectious bovine rhinotracheitis and parainfluenza 3 viruses (SmithKline Animal Health, Mississauga, ON, Canada), dewormed, and spayed before starting the experiment. The heifers had been obtained at an early age (3 mo) and conditioned to the environmental chambers used to measure CH4 before experimentation. This was done to minimize the stress on the cattle during the time they were in the chambers. Before the experiment, the heifers were fed a diet containing 70% barley silage, 15% steam-rolled barley grain, and 15% supplement containing protein sources, minerals, and vitamins (DM basis). At the start of the backgrounding phase, the heifers were approximately 9 mo old and weighed 328 ± 18 kg (mean ± SD).
During the experiment, the heifers were housed in individual pens bedded with straw in a sheltered, unheated barn. Daily feed intake, BW change, and ruminal fermentation were measured in this facility. Once during each phase, the cattle were moved to environmental chambers to measure gas emissions.
Diet and Treatments
The diets used were typical of diets fed in commercial feedlots in North America. The backgrounding diet consisted of 70% whole crop barley silage, 25% steam-rolled barley grain, and 5% supplement for the barley diet, and 70% corn silage, 18% dry-rolled corn grain, and 12% supplement for the corn diet (DM basis). The finishing diets consisted of 9% barley silage, 81.4% steam-rolled barley or dry-rolled corn, and 9.6% supplement (DM basis). The various supplements contained the supplemental protein sources, and provided minerals and vitamins in excess of NRC (1996) nutrient requirements for animals with an ADG of 1.0 kg/d. Diet composition is given in Table 1, with the chemical composition of the ingredients given in Table 2. The diets also contained 33 mg/kg of monensin (Rumensin 80; Elanco Animal Health, Indianapolis, IN). The cattle were adapted to the backgrounding diet over a 2-wk period and to the finishing diet over a 5-wk period. The transition to the finishing diet was done using a series of five diets with increasing concentrate proportion. Cattle assigned to barley or corn diets at the start of the study remained on their respective diets for the duration of the experiment.
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Measurements of Methane and Carbon Dioxide Emissions
Once during each phase, the cattle were moved to environmental chambers to determine CH4 and CO2 emissions. Chamber measurements were staggered for Groups 1 and 2 because only four chambers were available at a time. During the backgrounding phase, cattle were moved to the chambers for a 5-d period on the morning of d 14 for Group 1 and on d 28 for Group 2. Similarly, during the finishing phase, Group 1 was moved into the chambers on the morning of d 21, and Group 2 was moved on the morning of d 28.
Each chamber measured 4.4 m wide x 3.7 m deep x 3.9 m tall (63.5 m3; model C1330, Conviron, Inc., Winnipeg, Manitoba, Canada). Chamber air temperature was maintained at 10°C. Within each chamber, the animals were individually restrained in metabolism stalls that measured 2.5 m long x 0.9 m wide, elevated from the floor by 15 cm. Each stall was equipped with a feeder providing each animal with individual access to feed. Two animals were housed in each of the four chambers. The cattle were paired at the start of the experiment, such that the total BW of cattle per chamber and per treatment was similar. The pairing of animals was consistent throughout the experiment, such that animals within a chamber received the same treatment. The first day within the chambers was considered an adjustment period, allowing the heifers to adapt before measurements were recorded for three consecutive 24-h days. The cattle were returned to their individual stalls on the fifth day. Interruptions to the chambers occurred daily at 0730 when the floor was cleaned and at 0930 when cattle were fed. During the finishing phase, additional interruptions occurred when fecal samples were taken at 1530; however, these interruptions had little effect on the daily emissions because fluxes were calculated every 10 min and then averaged to derive the 24-h period emission value. When interruptions occurred the corresponding fluxes were omitted, allowing for reequilibration of the fluxes where the chamber time constant was 5 min.
Airflow and concentration of CO2 and CH4 were measured for the intake and exhaust ducts of each chamber. Details of the procedures used and the precision and accuracy of the technique are given by McGinn et al. (2004). Briefly, air velocity was measured three times over the day in each intake and exhaust duct (five points per duct) for each chamber (model 8330, TSI, Inc., Shoreview, MN). The air stream in each of the eight ducts was subsampled continuously and the CO2 concentration measured (model LI-6262, LI-COR, Inc., Lincoln, NE). In a similar manner, CH4 concentration in the intake duct of each chamber was measured continuously using another analyzer (model Ultramat 5E, Siemens, Inc., Karlsruhe, Germany). The CH4 concentration inside each chamber was measured using a open path laser (model GasView MC, Boreal Laser, Inc., Spruce Grove, Alberta, Canada) and shown by McGinn et al. (2004) to be related to the exhaust duct concentration because the chamber air was well mixed.
Emission Calculations
Details of the calculation of CO2 and CH4 emissions are reported by McGinn et al. (2004). In summary, the flux (F) of CH4 or CO2 for each chamber was calculated for each of the 3 d of measurement during each phase from the fresh air intake (i), chamber exhaust (e) concentration (Ci and Ce, respectively; ppm), and mean air velocity (Vi and Ve, respectively; m/s):
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where MW is the molecular weight of gas (g/mol), P is the barometric pressure (Pa), R is the universal gas constant (8.31 J•mole–1•deg K–1), T is the stream air temperature (deg K) and A is the cross sectional area of the duct (0.146 m2). The T/P value is a correction for the air velocity meter.
Although all instruments used to measure gas fluxes were calibrated, differences existed between chambers (e.g., error in measuring induct airflow). These between-chamber differences were documented by releasing the same amount of gas into each chamber (with no animals) and then determining whole-chamber flux when the exhaust concentration reached steady state (McGinn et al., 2004). The ratio of maximum flux (always Chamber 4) to other chamber fluxes was determined. The average correction factors relative to Chamber 4 were 1.01, 1.14, 1.13, and 1.00 for Chambers 1 to 4, respectively. These chamber corrections were also applied to the CO2 flux data. This procedure reduced the variability in emissions between chambers and improved the sensitivity to treatment differences.
Ruminal Fermentation Measurements
Ruminal pH was measured once per animal during each phase. Samples were taken 4 h after feeding on d 10 for Group 1 and d 17 for Group 2 during the backgrounding phase and on d 17 for Group 1 and d 24 for Group 2 during the finishing phase. A rubber tube was inserted into the rumen via the esophagus and rumen contents (400 mL) removed using an electric pump. Samples were monitored visually to ensure they were not contaminated with saliva. The pH was measured immediately using a pH meter (Accumet model 25, Denver Instrument Co., Arvada, CO). The whole contents were squeezed through four layers of cheesecloth. Five milliliters of the filtrate was combined with 1 mL of 25% (wt/vol) of meta-phosphoric acid and was stored frozen (–30°C) until VFA analysis.
Digestibility
Total-tract digestibility of nutrients was determined during 5-d collection periods in each phase of the experiment. During the backgrounding phase, feces were collected from d 20 to 24 for Group 1 and d 35 to 39 for Group 2, and during the finishing phase, from d 21 to 25 for Group 1 and d 28 to 32 for Group 2. Thus, during the backgrounding phase, the digestibility measurements were done when the animals were in individual pens, whereas during the finishing phase, the measurements were made during the time the animals were restrained in the chambers. The change in protocol during the finishing phase was made to accommodate the increasing difficulty of collecting feces from unrestrained animals. Digestibility was determined using an external marker prepared from chromic oxide and ground barley. Ten grams of marker, providing approximately 2 g of Cr, was top-dressed once daily onto the feed of individual animals for 10 d during each phase, starting 5 d before fecal collections began. In all cases, the entire allotment of marker was consumed. Fecal samples (100 g wet weight) were collected twice daily at 0930 and 1530 from the rectum of each animal, composited by heifer and phase as collected, and immediately frozen. The pooled samples were later dried at 55°C for 48 h in a forced-air oven, ground to pass a 1-mm screen, and analyzed for analytical DM, GE, NDF, ADF, and Cr. Additional fecal samples (100 g wet weight) were also taken from each animal before dosing the marker each phase. These samples were analyzed for DM and Cr. The Cr concentration in the feces taken predosing was used to adjust for residual marker excretion. The Cr concentration in fecal samples obtained before dosing was in all cases less than 1% of the Cr concentration in the fecal samples composited by phase; thus, this adjustment was trivial. Chromium was assumed to be completely indigestible and the digestibility of DM was calculated as follows:
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where DMI is the average DMI consumed during the 5-d period during which fecal samples were taken. Digestibility of OM, GE, NDF, and CP was calculated using the same approach.
Chemical Analyses
All chemical analyses were performed on each sample in duplicate, and where the CV for the replicate analysis was >5%, the analysis was repeated.
Ruminal VFA were quantified using colonic acid as the internal standard, and gas chromatography (model5890, Hewlett Parkard, Little Falls, DE) with a capillary column (30 m x 0.25 mm i.d., 1-µm phase thickness, bonded PEG; Supelco Nukol, Sigma-Aldrich Canada, Oakville, Ontario, Canada), and flame ionization detection. The oven temperature was 100°C for 1 min, which was then ramped by 20°C/min to 140°C, and then by 8°C/min to 200°C/min, and held at this temperature for 5 min. The injector temperature was 200°C, the detector temperature was 250°C, and the carrier gas was helium.
Analytical DM was determined by drying the samples at 135°C for 2 h, followed by hot weighing. The OM content was calculated as the difference between 100 and the percentage of ash (AOAC, 1995; Method 942). Gross energy was determined using an adiabatic calorimeter (model 1241, Parr, Moline, Il). The NDF and ADF were determined in the Ankom200 fiber analyzer (Ankom Technology Corp., Fairport, NY) using heat-stable 
-amylase and sodium sulfite. For the measurement of CP (N x 6.25), samples were ground using a ball mill (MM2000 mixer mill, Retsch, Haan, Germany) to a fine powder. Nitrogen was quantified by flash combustion with gas chromatography and thermal conductivity detection (Carlo Erba Instruments, Milan, Italy). Details of the starch procedure used are given by Rode et al. (1999). Chromium, Ca, and P were determined by inductively coupled plasma emission spectrometry (SpectoCirosCCD; Specto Analytical Instruments, GmbH and Co., Kleve, Germany) after dry-ashing and extraction of the respective mineral.
Calculations and Statistical Analyses
Cumulative daily CH4 and CO2 emissions from each chamber were calculated for each of the 3 d within each phase. The total DMI consumed by the two heifers within each chamber on the days that gases were measured also was calculated. The daily CH4 flux was then expressed per unit of DMI and as a proportion of GE intake of the two cattle within the chamber on that same day. The GE content of CH4 was assumed to be 13.3 Mcal/kg.
The data were analyzed using a Mixed procedure of SAS (SAS Inst., Inc., Cary, NC). The individual animal was the experimental unit for intake, BW, digestibility, and ruminal fermentation variables because these data were obtained from individually penned animals. For these variables, the model included the fixed effects of phase (backgrounding and finishing), diet (corn and barley), the interaction between phase and diet, and the random effects of group and animal. Phase was treated as a repeated measure, and subject was the animal. The compound symmetry method was used to estimate the variance components. The chamber, representing data for two animals, was the experimental unit for CH4 and CO2 measurements. The model used for CH4 and CO2 measurements included the fixed effects of phase (backgrounding and finishing), diet (corn and barley), day (1 to 3) and their interactions, and the random effect of chamber. Phase and day were treated as repeated measures, with chamber as the subject, using the unstructured method to estimate the variance components. Treatment effects were declared significant at P < 0.05, and trends were discussed at P < 0.10. When the interaction between phase and diet was significant (P < 0.05), the effect of diet within phase was examined for significance (P < 0.05).
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Results |
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TopAbstractIntroductionExperimental ProceduresResultsDiscussionImplicationsLiterature Cited |
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). During the backgrounding phase, animals fed a corn diet consumed more feed than those fed a barley diet, whereas intake did not differ for cattle fed either diet during the finishing phase. Greater intake by cattle fed corn during the backgrounding phase resulted in greater ADG compared with cattle fed barley. During the finishing phase, there was no effect of grain source on ADG, but weight gain and feed intake during the finishing phase was less than industry standards for cattle fed corn- and barley-based diets because of the short time on feed.
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). During both production phases, pH was lower for cattle fed corn than for those fed barley. Total VFA was greater during the finishing phase than during the backgrounding phase, reflecting the high rate of ruminal availability of high-grain diets compared with high-forage diets. Total VFA tended (P = 0.06) to be greater for cattle fed corn than barley, which reflected the greater intake of cattle fed corn during the backgrounding stages and the numerically greater intake of cattle fed corn during the finishing phase. The greater VFA of cattle fed corn is consistent with the lower ruminal pH of these cattle. Proportions of acetate, butyrate, iso-butyrate, and iso-valerate were greater, whereas proportions of propionate and valerate were lower during the backgrounding phase than during the finishing phase. Cattle fed corn had higher proportions of acetate and tended (P = 0.06) to have lower proportions of propionate in their ruminal fluid. Source of grain had no effect on butyrate or valerate proportions. Feeding corn decreased isobutyrate proportion and tended (P = 0.09) to decrease isovalerate proportion during the backgrounding phase, but corn had no effect during the finishing phase. Acetate:propionate ratio was lower during finishing than during backgrounding as expected, but the effect of diet depended on the phase, as evidenced by an interaction between phase and diet. Cattle fed corn during the backgrounding phase had higher acetate:propionate ratio, whereas during the finishing phase, there was no difference between the diets.
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). However, within phase, there was no effect of diet on digestibility, except in the case of CP, which was less for cattle fed corn than for those fed barley.
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). This difference between production phases was not eliminated by correcting emissions for intake of DM or GE; however, effects of grain source on CH4 emissions depended on phase. Daily methane emissions per animal were 32% greater when a corn backgrounding diet was fed compared with feeding a barley backgrounding diet, but grain source had no effect on CH4 emissions from finishing diets. However, when expressed on the basis of DMI or GE intake, CH4 emissions during the backgrounding phase were not affected by grain source, whereas emissions were less for the corn finishing diet than for the barley finishing diet.
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Discussion |
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TopAbstractIntroductionExperimental ProceduresResultsDiscussionImplicationsLiterature Cited |
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). Ionophores typically decrease CH4 emissions by up to 25%, although their effects can be short-lived (Johnson and Johnson, 1995).
The ad libitum intakes and the ADG reported for cattle in this study during the finishing phase were less than typically reported for cattle fed these types of diets (Owens et al., 1997; Block et al., 2001). In a commercial feedlot situation, cattle are typically slaughtered at a live weight of approximately 560 kg. In contrast, the final BW of the cattle in this study was only 450 kg, which is considerably less than the industry standard. However, this experiment was not designed to illustrate differences in gain and production efficiency of cattle fed corn- or barley-based diets because of the limited number of animals used, combined with the fact that cattle were moved to metabolism stalls within chambers twice during the experiment. When animals were moved to the chambers, DMI dropped by approximately 31% during the backgrounding phase and by 22% during the finishing phase due to the stress associated with the change in environment, as well as the decreased energy expenditure due to the decreased activity of the cattle while restrained. Effects of grain source on animal performance have been reported by others (Owens et al., 1997; Koenig and Beauchemin, 2005).
Average CH4 emissions in this study ranged from a low of 62 g/d for cattle fed a corn finishing diet to 171 g/d for cattle fed a corn backgrounding diet. In comparison, the IPCC (Houghton et al., 1996) CH4 emission value for a steer is 129 g/d (Tier 1, cool climate countries). However, our estimates of CH4 underestimate the CH4 emissions of commercial feedlot cattle because of the decrease in intake during CH4 measurements, which is an inherent problem with studies conducted in metabolic chambers. Methane emissions adjusted to compensate for the drop in intake were 254 and 185 g/d for the corn and barley background diets, and 79 and 108 g/d for the corn and barley finishing diets, respectively. This adjustment assumes that CH4 emissions are a linear function of intake in that range. Our minimum and maximum adjusted values are 61 and 197% of the value used by the IPCC (Houghton et al., 1996). Our data clearly indicate that the Tier 1 IPCC value (Houghton et al., 1996) used to calculate greenhouse gas emissions from the feedlot industry may over-or underestimate emissions depending on the diet fed.
Greater methane emissions from cattle fed high-forage backgrounding diets than for those fed high-concentrate diets was expected because methane emissions decrease as the proportion of concentrate in the diet increases (Johnson and Johnson, 1995). From our study, it is evident that the source of grain can also have dramatic consequences on enteric CH4 production from feedlot cattle. Some of the differences between corn and barley diets observed in the present study can be attributed to small differences in DMI. For example, for backgrounded cattle, greater enteric CH4 production of cattle fed a corn diet compared with those fed a barley diet was a reflection of numerically greater DMI because when CH4 emissions were expressed on the basis of DMI, source of grain in the backgrounding diet had no effect on emissions.
Approximately 7.4% of GE intake was lost as CH4 during the backgrounding phase, which was greater than the range of 6.5 to 7.1% of GE previously reported for cattle fed backgrounding diets containing 75% barley silage and 25% barley based concentrate (McGinn et al., 2004). The slightly higher proportion of concentrate used in the present study would be expected to result in slightly lower methane emissions than reported previously. Differences in estimates of CH4 emissions can sometimes be attributed to measurement techniques (Johnson and Johnson, 1995); however, the same chamber technique was used in both studies to measure CH4, although the chambers were maintained at 10°C in this study compared with 15°C used previously. These temperature differences would have only minor effects on methane emissions and would not fully account for differences between these two studies (Moss, 2002). The difference between the studies is likely due to the differences between animals and the greater GE content of the backgrounding diet (due to higher forage quality) used by McGinn et al. (2004) compared with the present study.
Feeding a high-concentrate diet during the finishing phase decreased CH4 losses by 38% in the case of barley diets and by 64% in the case of corn diets compared with the high-forage diets fed during the backgrounding phase. The decrease in methane emissions observed between phases was consistent with observed changes in individual VFA proportions, particularly the decrease in acetate proportion and concomitant increase in propionate proportion. Formation of acetate in the rumen promotes CH4 production, whereas propionate production and methanogenesis are competing processes (Moss et al., 2000).
Grain source influenced the amount of energy lost as enteric CH4 during the finishing phase, when emissions were expressed on the basis of DMI. Lower CH4 losses for cattle fed corn than for those fed barley could have been mediated through differences in ruminal fermentation; however, observed concentrations of total VFA and molar proportions of acetate, propionate, and butyrate in ruminal fluid do not support greater CH4 for cattle fed corn. Cattle fed the corn diet tended to have greater total VFA production, as well as higher proportions of acetate and lower proportions of propionate than cattle fed barley. Lower methane emissions can also be due to a shift in the site of digestion from the rumen to the intestines, and rolled corn is typically less extensively digested in the rumen than rolled barley (Yang et al., 1997). However, it is not clear that corn was less extensively digested in the rumen than barley in this study because ruminal pH was lower and VFA concentration was greater for corn than for barley. It is possible that the effect of grain source on CH4 production of cattle fed feedlot finishing diets could have been mediated through ruminal pH. Fermentation acids produced in the rumen are toxic to methanogenic bacteria at pH less than 6 (Van Kessel and Russell, 1996). Thus, concentrate diets that decrease pH result in less CH4 production, as was the case with the corn-based finishing diet in this study.
The 2.8% loss of GE intake as CH4 observed for cattle fed corn during the finishing phase was similar to the expected range of 2 to 4% of GE for feedlot cattle fed in excess of 80% corn grain (Johnson et al., 1994; Johnson and Johnson, 1995). The 4.0% loss of GE as CH4 observed for the barley finishing diet was greater than observed for the corn diet, but was considerably less than the range of 6.5 to 12% reported previously for barley diets (Hashizume et al., 1968, Whitelaw et al., 1984). Based on those two studies, Johnson et al. (2000) suggested that high-grain barley diets result in greater CH4 than would be expected from high-grain corn diets; however, the experimental conditions used in those previous studies were not representative of the North American feedlot industry. The study by Hashizume et al. (1968) used two mature cows consuming 5.2 to 8.6 kg/d, and the diets contained only 26 to 41% ground or steam-rolled barley. Methane losses ranged from 7.4 to 11.6% of GE. The study by Whitelaw et al. (1984) used cattle weighing 250 kg, but they were fed restricted amounts (70% of ad libitum intake, approximately 3.8 kg/d) of a pelleted diet containing 85% barley and 15% protein supplement. Methane losses ranged from 10.6 to 11.5% of GE. Based on the results of the present study, it seems that CH4 emissions from feedlot cattle fed high-grain barley diets are slightly greater than would be expected from cattle fed corn diets, and slightly greater than the value of 3.5% of GE used by IPCC for feedlot cattle (Houghton et al., 1996).
The daily CO2 emissions of cattle during the back-grounding phase were similar to mean values (3.1 to 3.6 kg/d) previously reported by our group for cattle fed backgrounding diets based on barley silage and barley grain (McGinn et al., 2004). Increased respiration of CO2 in the finishing phase compared with the back-grounding phase was consistent with the greater energy intake and metabolic rate of the heavier cattle fed higher grain diets (Brouwer, 1965). The CO2 emissions observed in the present study were similar to the 3.2 kg of CO2•animal–1•d–1 reported by Kinsman et al. (1995) for dairy cows, but greater than the 1.0 and 1.3 kg/d (using a conversion factor of 1,870 L/kg) reported for yearling beef heifers by Boadi et al. (2002). However, CO2 respired by livestock is not reported by the IPCC as a net emission (Houghton et al., 1996). The carbon released as CO2 during respiration is considered to have been previously captured from the atmosphere by the plants through photosynthesis.
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TopAbstractIntroductionExperimental ProceduresResultsDiscussionImplicationsLiterature Cited |
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Footnotes |
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2 Correspondence: Box 3000, 5403 1st Ave. South (phone: 403-327-4561; fax: 403-317-2182; e-mail: beauchemin{at}agr.gc.ca).
Received for publication August 18, 2004. Accepted for publication December 10, 2004.
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TopAbstractIntroductionExperimental ProceduresResultsDiscussionImplicationsLiterature Cited |
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