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    • "La medición de las emisiones de metano (CH 4 ) de rumiantes se realiza, generalmente, utilizando la técnica del trazador hexafluoruro de azufre (SF 6 ) originalmente desarrollada por Johnson y Johnson (1995). Esta técnica permite la cuantificación diaria de CH 4 por animal y es internacionalmente reconocida como la más apropiada para medir las emisiones de metano en sistemas de pastoreo en virtud que los equipos se instalan sobre el animal sin impedir ni limitar sus movimientos ni sus hábitos en la pastura (Johnson et al., 2007; Lassey et al., 1997; Woodward et al., 2004; Grainger et al., 2007). La utilización del SF 6 responde a que es un gas considerado como el mejor trazador para medir la cantidad de metano emitido por los rumiantes, debido a que posee una elevada estabilidad en el rumen de los animales, inclusive superior a la de gases isótopos del metano. "
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    • "To correct for background atmospheric concentrations of methane within the housing facility, gas samples were collected from the ambient air using 3 collection canisters per day, hung at various locations within the shed. At the end of the collection period, sample concentrations of SF 6 and methane were determined via gas chromatography as described by Johnson et al. (2007) using a Varian 3800 gas chromatograph (Varian Inc., Palo Alto, CA). "
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    ABSTRACT: This study examined the relationship of residual feed intake (RFI) and performance with methane emissions, rumen fermentation and digestion in beef heifers. Individual dry matter intake (DMI) and growth performance were measured for 22 Simmental heifers (mean initial BW 449kg, SD = 46.2 kg) offered grass silage ad libitum for 120 d. Ultrasonically scanned muscle and fat depth, BCS, muscularity score, skeletal measurements, blood variables, rumen fermentation (via stomach tube) and total tract digestibility (indigestible marker) were measured. Methane production was estimated using the sulphur hexafluoride tracer gas technique over two 5-day periods beginning d 20 and 75 of the RFI measurement period. Phenotypic RFI was calculated as actual DMI minus expected DMI. The residuals of the regression of DMI on ADG and mid-test metabolic body weight (MBW), using all heifers, were used to compute individual RFI coefficients. Heifers were ranked by RFI and assigned to low (efficient), medium or high (inefficient) groupings. Overall ADG and DMI were 0.58 kg (SD = 0.18) and 7.40 kg (SD = 0.72), respectively. High RFI heifers consumed 9% and 15% more (P < 0.05) than medium and low RFI groups, respectively. Body weight, growth, skeletal or composition traits did not differ (P > 0.05) between low and high RFI groups. High RFI heifers had higher concentrations of plasma glucose (6%) and urea (13%) and lower concentrations of plasma creatinine (9%) than low RFI heifers (P < 0.05). Rumen pH and apparent in vivo digestibility did not differ (P > 0.05) between RFI groups although acetate: propionate ratio was lowest (P = 0.07) for low RFI (3.5) and highest for high RFI (4.6) heifers. Methane production expressed as g/d or g/kg metabolic body weight were greater (P < 0.05) for high (297 g/d and 2.9g/kg BW(0.75)) compared with low (260 g/d and 2.5 g/kg BW(0.75)) RFI heifers, with medium (275 g/d and 2.7 g/kg BW(0.75)) RFI heifers intermediate. Regression analysis indicated that a 1 kg DM/d increase in RFI was associated with a 23 g/d increase (P = 0.09) in methane emissions. Results suggest that improved RFI will reduce methane emissions without affecting productivity of growing beef cattle.
    Journal of Animal Science 10/2013; 91(12). DOI:10.2527/jas.2013-6956 · 2.11 Impact Factor
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    • "This could suggest that the stability of permeation tubes at high rates is not as robust as lower rates, and/or that the molar proportion of SF 6 in the breath sample, relative to that of CH 4 , decreases as the RR of SF 6 in the rumen increases. As gas-mixing processes within the rumen headspace, as well as during eructation, are highly turbulent, it would not be expected that such mixing could discriminate between CH 4 and the nine-fold heavier SF 6 molecules (Johnson et al., 2007). Alternatively, it can be hypothesised that the SF 6 gas released in the reticulum or the ventral sac of the rumen, where the permeation tube sits, does not reach the ruminal headspace gas pool available for eructation. "
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    ABSTRACT: The release rate (RR) of sulphur hexafluoride (SF(6)) gas from permeation tube in the rumen appears to be positively related with methane (CH(4)) emissions calculated using the SF(6) tracer technique. Gas samples of breath and ruminal headspace were collected simultaneously in order to evaluate the hypothesis that transactions of SF(6) in the rumen are the source for this relationship. Six non-lactating dairy cows fitted with rumen cannulae were subdivided into two groups and randomly assigned to a two-period crossover design to permeation tubes with low RR (LRR = 1.577 mg/day) or two-times higher RR (HRR = 3.147 mg/day) RR. The cows were fed limited amounts of maize silage (80% ad libitum) split into two meals (40% at 0800 h and 60% at 1600 h). Each period consisted of 3-day gas sampling. Immediately before the morning feed and then each hour over 8 h, ruminal gas samples (50 ml) were withdrawn through the cannula fitted with stoppers to prevent opening. Simultaneously, 8-h integrated breath gas samples were collected over the same period. Ratios of concentration of CH(4)/SF(6), CO(2)/SF(6) and CO(2)/CH(4) and emission estimates of CH(4) and CO(2) were calculated for each sample source using the SF(6) tracer technique principles. The LRR treatment yielded higher (P < 0.001) ruminal CH(4)/SF(6) (by 1.79 times) and CO(2)/SF(6) (by 1.90 times) ratios than the HRR treatment; however, these differences were lower than the 2.0 times difference expected from the RR between the LRR and HRR. Consequently, the LRR treatment was associated with lower (P < 0.01) ruminal emissions of CH(4) over the 8-h collection period than with the HRR treatment (+11%), a difference also confirmed by the breath samples (+11%). RR treatments did not differ (P = 0.53) in ruminal or breath CO(2) emissions; however, our results confirm that the SF(6) tracer seems inappropriate for CO(2) emissions estimation in ruminants. Irrespective of the RR treatment, breath samples yielded 8% to 9% higher CH(4) emission estimates than the ruminal samples (P = 0.01). The relationship between rumen and breath sources for CH(4) emissions was better for LRR than for HRR treatment, suggesting that tracer performance decreases with the highest RR of SF(6) tested in our study (3.1 mg/day). A hypothesis is discussed with regard to the mechanism responsible for the relationship between RR and CH(4) emission estimates. The use of permeation tubes with small range in RR is recommended in animal experiments to decrease variability in CH(4) emission estimates using the SF(6) tracer technique.
    animal 03/2012; 6(3):518-25. DOI:10.1017/S175173111100156X · 1.84 Impact Factor
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