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3139J. Dairy Sci. 95 :3139-3148

http://dx.doi.org/ 10.3168/jds.2011-4298

© American Dairy Science Association

, 2012 .

ABSTRACT

The objectives of the present study were to compare the sulfur hexafluoride (SF 6 ) and respiration chamber techniques for measuring methane (CH 4 ) emissions from dairy cows and to determine the proportion of CH 4 that is released through the rectum. Data used were derived from 20 early lactation dairy cows in a 2 ×

2 factorial design study for 4 periods with 6 wk/period.

The 4 treatment diets consisted of grass silage and 2 levels of concentrate (30 and 60% dry matter basis), with or without yeast supplement. At the end of each period, CH4 emissions were measured simultaneously using the SF 6 and respiration chamber techniques when cows were housed in chambers. The SF 6 technique was also used when cows were housed in digestibility units (barn location) before and after respiratory chamber measurements (chamber location). The simultaneous measurements in chamber location revealed that CH 4 emission estimates by the SF 6 technique were similar to those by the respiration chamber technique in the first

3 periods, although the SF

6 estimates were significantly higher in period 4. The regression of all data from the

4 periods demonstrated a linear relationship between

the SF6 and respiration chamber measurements for total CH 4 emissions (g/d, R 2 = 0.69) and for CH 4 emis- sions per unit of milk yield (g/kg, R 2 = 0.88), and a quadratic relationship for CH 4 emissions per unit of dry matter intake (g/kg, R 2 = 0.64). The CH 4 emis- sions from the rectum were calculated as the difference between CH 4 estimates from the SF6 technique when cows were housed in respiratory chambers and barn lo- cations, which was 3% of the total CH 4 emissions from the mouth, nostrils, and rectum. The SF 6 estimates in

the chamber location accounted for all sources of emis-sions, whereas those in the barn location, like that in grazing conditions, did not include CH

4 emission from the rectum. Therefore, the SF 6 measurements for graz- ing cattle should be adjusted for CH 4 emissions from the rectum (3% of total). We conclude that the SF 6 technique is reasonably accurate for estimating CH

4emissions. Key words: methane , sulfur hexafluoride tracer tech-

nique , respiration chamber , dairy cow

INTRODUCTION

Accurate and reliable measurements of methane (CH

4 emissions from individual animals have traditionally been made using respiration chambers. However, they require trained animals, restricted animal movement, and have a high labor input and expense (Johnson et al., 2007), and their results might not be extrapolated to free-ranging animals (Pinares-Patiño and Clark,

2008). A technique that makes use of the inert tracer

gas sulfur hexafluoride (SF 6 ) has been developed for estimating CH 4 emission rates from ruminants under grazing conditions (Johnson et al., 1994). In recent years, some studies have examined the va- lidity of the SF6 tracer technique for estimating CH 4 emissions. Most studies with beef cattle and sheep found statistical agreement between CH 4 emissions es- timated by the SF 6 and respiration chamber techniques (Ulyatt et al., 1999; Boadi et al., 2002; McGinn et al.,

2006; Johnson et al., 2007; Pinares-Patiño et al., 2011),

although not all (Wright et al., 2004; Pinares-Patiño et al., 2008a). The accuracy of this technique for lactat- ing dairy cows is less clear, as McCourt et al. (2008) indicated that CH 4 measured using the SF 6 technique was 75% of that measured using respiration chambers, whereas Grainger et al. (2007) reported a ratio of 102% between the estimates from the SF6 and respiration chamber techniques. In both studies, the technique comparison was done with dairy cows in mid lactation.

No comparisons between SF

6 and respiration chambers Comparison of the sulfur hexafluoride tracer and respiration chamber techniques for estimating methane emissions and correction for rectum methane output from dairy cows

C. Muñoz ,*†

1 T. Yan ,* D. A. Wills ,* S. Murray ,* and A. W. Gordon ‡

† Instituto de Investigaciones Agropecuarias (INIA) Remehue, Osorno, Región de Los Lagos 5290000,

Chile

Received February 23, 2011.

Accepted January 17, 2012.

1

Corresponding author: camila.munoz@inia.cl

3140MUÑOZ ET AL.

Journal of Dairy Science Vol. 95 No. 6, 2012

have been made at different stages of lactation, espe- cially for early lactation cows with high CH 4 emissions.

In grazing ruminants, the SF

6 technique estimates CH 4 exiting through the mouth and nostrils, but not through the rectum. In an early study conducted in sheep using an isotope tracer method, Murray et al. (1976) reported that the magnitude of CH 4 excreted through the rectum was less than 2% of the total CH 4 produced by an animal, despite 13% of the total CH 4 being produced by the hindgut. Consequently, it is expected that CH 4 estimates measured using the SF 6 technique should be slightly lower than actual total CH 4 emissions. However, little information is available for correction of SF 6 measurement for CH 4 emissions from the rectum of grazing cattle. The objectives of the present study were to 1) com- pare the SF 6 tracer technique with the respiration chamber technique for measuring CH 4 emissions from individual dairy cows and 2) determine the proportion of CH 4 that is excreted through the rectum compared with total enteric CH 4 emissions.

MATERIALS AND METHODS

The work described in the present paper was con-

ducted at the Agri-Food and Biosciences Institute (AFBI), Hillsborough, UK, in accordance with the re- quirements of the UK Animals (Scientific Procedures) Act 1986 and with the approval of the AFBI (Hillsbor- ough) Ethical Review Group.

Animals, Experimental Design, and Diets

The data used in the present study were obtained

from a 2 (concentrate level) × 2 (yeast supplement) factorial design study with 4 periods (6 wk/period). Twenty early lactation dairy cows (56 ± postpar- tum) were used, which were of 3 genotypes (4 Norwe- gian, 4 Norwegian × Holstein-Friesian, and 12 Holstein- Friesian) and had various parities (4 primiparous and

16 multiparous cows). Nutritional treatments consisted

of 2 levels of concentrate (30 and 60%, DM basis), without or with yeast supplement at 0.5 g/d (Levucell SC20; Lallemand SAS, Blagnac Cedex, France). There was a 3-wk interval between periods 1 and 2, 2 and

3, and 3 and 4, so each cow was on treatments for 33

wk. The experimental design aimed to maximize the range of feed intake and, thus, CH 4 emissions, which was expected to increase the accuracy of validation of the SF 6 technique. Throughout the present study, cows were offered ad libitum their experimental diets once daily in the morn-

ing as a TMR of grass silage and concentrates. They were allowed free access to water, and milked twice dai-ly at approximately 0700 and 1600 h. The grass silages had pH 3.9 and contained 28.2% DM, 18.4 MJ of gross energy/kg of DM, and 13.2% CP, 46.4% NDF, 30.1% ADF, and 8.6% ash on a DM basis. Concentrates were based on soybean meal, rapeseed meal, barley, corn, soybean hulls, and citrus pulp.

During each period, animals were housed as a single group in a cubicle accommodation for the first 30 d. Afterward, cows were placed in individual stalls in di- gestibility units for 4 d, with feed intake recorded and CH 4 emissions estimated using the SF 6 technique (de- scribed later) during the final (barn location before chamber measurements). They were then transferred to indirect open-circuit respiration chambers where they stayed for 4 d, with feed intake recorded and CH 4 emis- sions measured simultaneously by both the SF 6 and respiration chamber techniques (chamber measurement described later) during the last (chamber location). After completion of chamber location measurements, cows were returned to the digestibility units for the final of each period, with feed intake recorded and CH 4 emissions estimated using the SF 6 technique during the final (barn location after chamber measurements). There were 2 respiration chambers and cows were paired based on their calving dates and treatment allocation at the beginning of each period to progress through the measurement sequence. At the end of periods 1, 2, and

3, cows were returned to the group for a 3-wk interval

before the start of the next feeding period. SF 6

Tracer Measurements

The technique originally developed by Johnson

et al. (1994) was used to determine individual daily CH 4 emissions using the SF 6 tracer gas. A week before the beginning of the first CH 4 measurements, a brass permeation tube containing SF 6 gas of known release rate was placed in the rumen of each cow. The SF 6 release rate and expected lifetime for each tube were calculated using prefilling weight of SF 6 gas and a 6-wk serial of weights measured at a controlled environment (39°C). The release rates of SF 6 tubes ranged from 4.10 to 6.39 mg/d, with a mean of 5.39 mg/d, and the cor- responding values for lifespan were 374 to 540 and 456 d, respectively. During the course of periods 1 to 4, CH 4 measurements were carried out when tubes were deployed in the rumen of cows between 7 and 262 d, with an average of 29, 98, 161, and for periods 1,

2, 3, and 4, respectively.

Before and after being in the respiratory chamber

(barn location), on the first day of CH 4 measurements, a head collar was placed on each cow sustaining a gas Journal of Dairy Science Vol. 95 No. 6, 2012SULFUR HEXAFLUORIDE METHANE EMISSIONS FROM DAIRY COWS 3141
collection tube running from just above the animal"s nostrils to a gas collection canister. The gas collection tube connected one after the other, an airline (6.35-mm diameter), a 15-μm filter, and a capillary tube with an evacuated polyvinyl chloride (PVC) canister. As the vacuum within the canister began to dissipate, a sample of air from around the cow"s mouth and nostrils was collected. The restriction given by the capillary tube allowed a flow rate of around 0.60 mL/min, which filled the canister to around 0.5 atmosphere pressure over a 24-h period. For the chamber location, as the air inside the chamber was completely mixed by an air-conditioning system, the gas-collection canister was located in the back of each chamber with the end of the airline placed inside the air duct that exits the chamber, through which air was circulated toward gas analyzers.

The SF

6 and CH 4 concentrations in the sampling can- isters were determined by GC (Varian 3600 GC; Varian Inc., Palo Alto, CA) fitted with a 6 Port Valve 200 and plumbed to a 1041 injector. Samples were injected through a 1-mL sample loop at a flow rate of 30 mL/ min using nitrogen as the carrier gas. All samples were analyzed in duplicate. After injection, the sample was split in 2 (50:50) for the determination of CH 4 and SF 6 simultaneously. The CH 4 -packed column (1.2-m length and 2-mm i.d.; Varian Inc., Walnut Creek, CA) was a stainless steel Porapak N (80-100 mesh), whereas the SF 6 -packed column (1.8-m length and 2-mm i.d.; Var- ian Inc.) had a molecular sieve 5A (45-60 mesh). The operating and conditioning temperatures of the injector and columns were both 70 and 120°C, respectively. A flame ionization detector was used for the detection of CH 4 (250°C; JVA Analytical, Dublin, Ireland), whereas the SF 6 concentration was measured using an electron capture detector (300°C; JVA Analytical). The gas chromatograph was calibrated weekly using 3 gas stan- dards (Scott-Marrin Inc., Riverside, CA). Standards were gas mixtures of 10, 150, and 300 ppt SF 6 with 10,

100, and 300 ppm CH

4 , corresponding to low, medium, and high concentrations of each gas, respectively. The medium standard was run at the beginning and end of each day.

Methane emissions (CH

4

Q; L/d) were calculated from

the measured SF 6 and CH 4 concentrations sampled by the canisters (SF 6

C and CH

4

C), background SF

6 and CH 4 concentrations (SF 6

B and CH

4

B), the predeter-

mined release rate of SF 6 from the permeation tubes (SF 6

Q), and the molecular weight (MW) of the gases

according to the following equation: CH 4

Q = (CH

4

C - CH

4

B)/(SF

6

C - SF

6 B)

× SF

6

Q × MW of CH

4 /MW of SF 6 .The unit for CH 4 emission as L/d was then converted to g/d. When applying the SF 6 technique in the cham- bers, air sampled at the chamber inlet was used to determine SFquotesdbs_dbs19.pdfusesText_25

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