Discussion of methods

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SF6 vs Respiration Chamber

For large-scale evaluation of CH4 emissions by individual animals, the SF6 technique is more useful than respiration chambers. Animal behaviour and intake might be affected by wearing the apparatus, and by daily handling to exchange canisters, but the technique is considerably less intrusive than respiration chambers because cows remain in the herd. Labour and monetary costs for changing canisters each day and for lab analysis are high. Throughput is limited by the number of sets of apparatus available, handling facilities, labour, and the capacity of the lab for gas analysis. Animals need to be measured for 5 to 7 days, and it is recommended that group size should be less than 15 animals (Berndt et al., 2014[1]), so maximum throughput would be about 750 animals per year. The method may be better suited for in housed conditions because of the labour and the potential movement restriction of the animals due to wearing the apparatus.

Breath sampling during milking and feeding vs Respiration Chamber

For large-scale evaluation of CH4 emissions by individual animals, breath-sampling methods have significant advantages compared with other methods. Breath-sampling methods are non-invasive because, once installed, animals are unaware of the equipment and are in their normal environment. Animals follow their normal routine, which includes milking and feeding, so no training of animals, handling, or change of diet is required. Equipment is relatively cheap, although more expensive gas analysers are available, and running costs are negligible.

The compromise for non-invasiveness of breath-sampling is that concentrations of gases in the sampled air are influenced by cow head position relative to the sampling tube (Huhtanen et al., 2015[2]). The use of head position sensors and data filtering algorithms can remove the effects when the cow’s head is completely out of the feed bin (Difford et al., 2016[3]), but not within the feed bin. Consequently, sniffer measurements are more variable than flux methods, with factors like variable air flow in the barn increasing measurement error (imprecision), and head position, a highly repeatable character, inflating between-cow variability.

Using CO2 as a tracer gas partly addresses the issue but, because CO2 arises from metabolism as well as rumen fermentation, variability of CO2 emissions has to be considered. A further consideration is diurnal variation in breath concentrations of CH4 and CO2 because animals are spot-sampled at different times of day and night. Diurnal variation can be accounted for either by fitting a model derived from the whole group of animals, or by including time of measurement in the statistical model (Lassen et al., 2012[4]).

The number of observations per analyser is limited only by number of cows assigned to one automatic milking station or concentrate feeding station and length of time equipment is installed. Typically, each analyser will record 40 to 70 animals 2 to 7 times per day for 7 to 10 days, although the number of sampling stations per analyser can be increased by using an automatic switching system (Pszczola et al., 2017[5]). Throughput per analyser is likely to be 2,000 to 3,000 animals per year.

NDIR vs LMD

Both methods are low invasive. LMD needs larger labor force, wheras NDIR can be used during milking and feeding. According to Rey at al. (2019)[6], the repeatability of the CH4 concentration was greater for NDIR (0.42) than for LMD (0.23). Correlation between methods was moderately high and positive for CH4 concentration (0.73 and 0.74,respectively) and number of peaks (0.72 and 0.72, respectively), and the repeated measures correlation and the individual-level correlation were high (0.98 and 0.94, respectively). A high coefficient of individual agreement for the CH4 concentration (0.83) and the number of peaks (0.77) were observed between methods. The study suggests that methane concentration measurements obtained from NDIR and LMD cannot be used interchangeably. But the use of both methods could be considered for genetic selection purposes or for mitigation strategies only if sources of disagreement, which result in different between subject and within-subject variabilities, are identified and corrected for.

Greenfeed

A limitation of the GreenFeed system is that animals require training to use the system, although animals which have been trained to use the system will readily use it again (Velazco et al., 2014[7]). However, some animals will not use the system or will use it infrequently, and frequency of visits is affected by diet (Hammond et al., 2016B[8]). This can be a challenge when screening commercial herds for CH4 emission under genetic evaluation. On the other hand, animals seem to get used to the equipment rapidly, and the sound produced by the system is remembered by the animals easily (personal information Dr. Finocchiaro). Alternatively, as practised in Canada, the unit is moved to individual animals in a tie-stall setting multiple times a day (personal information Prof C.F. Baes). Thus, action of individual animals is not needed. The manufacturer recommends 15 to 25 animals per GreenFeed unit, and recordings are made typically for 7 days. If all animals visit the unit adequately, throughput per unit is likely to be 750 to 1,250 animals per year. Sebek et al. (2019A, B)[9] and Bannink et al. (2018)[10] showed the usefulness of the GreenFeed method in an on farm setting.

Laser Methane Detector

The LMD can be used in the animal’s normal environment, although for consistency restraint is required during measurement. Because the LMD measures CH4 in the plume originating from the animal’s nostrils, results can be affected by factors such as: distance from the animal; pointing angle; animal’s head orientation and head movement; air movement and temperature in the barn; adjacent animals; and operator variation (Sorg et al., 2017[11]). Operator variation is likely to be one of the biggest factors because the operator controls distance and pointing angle, and is responsible for ensuring the laser remains on target. The structure of the barn and the resulting ventilation conditions and wind speed at the location of the measurement are also considerable sources of variation in recorded CH4. Assuming operator fatigue does not limit measurements, each LMD could record up to 10 animals per hour. If each animal is recorded 3 times (on 3 consecutive days, for example, as in Mühlbach et al. (2018)[12]), throughput is likely to be up to 1000 animals per year.

  1. ↑ Berndt, A., Boland, T.M., Deighton, M.H., Gere, J.I., Grainger, C., Hegarty, R.S., Iwaasa, A.D., Koolaard, J.P., Lassey, K.R., Luo D., Martin, R.J., Martin, C., Moate, P.J., Molano, G., Pinares-Patiño, C., Ribaux, B.E., Swainson, N.M., Waghorn, G.C., and Williams, S.R.O. 2014. Guidelines for use of sulphur hexafluoride (SF6) tracer technique to measure enteric methane emissions from ruminants. Pages 166. M. G. Lambert, ed. New Zealand Agricultural Greenhouse Gas Research Centre, New Zealand.
  2. ↑ Huhtanen, P., Cabezas-Garcia, E.H., Utsumi, S., and Zimmerman, S. 2015. Comparison of methods to determine methane emissions from dairy cows in farm conditions. J. Dairy Sci. 98:3394–3409. doi:10.3168/jds.2014-9118.
  3. ↑ Difford, G.F., Lassen, J., and Løvendahl, P. 2016. Interchangeability between methane measurements in dairy cows assessed by comparing precision and agreement of two non-invasive infrared methods. Comput. Electron. Agric. 124:220–226. doi:10.1016/j.compag.2016.04.010.
  4. ↑ Lassen, J., Lovendahl, P., and Madsen, J. 2012. Accuracy of noninvasive breath methane measurements using Fourier transform infrared methods on individual cows. J. Dairy Sci. 95:890-898.
  5. ↑ Pszczola, M., Rzewuska, K., Mucha, S., and Strabel, T. 2017. Heritability of methane emissions from dairy cows over a lactation measured on commercial farms. J. Anim. Sci. 95:4813-4819. doi: 10.2527/jas2017.1842.
  6. ↑ Rey, J., Atxaerandio, R., Ruiz, R, Ugarte, E., Gonzalez-Recio, O., Garcia-Rodriguez, A., and Goiri, I. 2019. Comparison Between Non-Invasive Methane Measurement Techniques in Cattle. Animals 9(8): 563. https://doi.org/10.3390/ani9080563
  7. ↑ Velazco, J.I., Cottle, D.J., and Hegarty, R.S. 2014. Methane emissions and feeding behaviour of feedlot cattle supplemented with nitrate or urea. Anim. Prod. Sci. 54:1737–1740. doi:10.1071/AN14345.
  8. ↑ Hammond, K.J., Jones, A.K., Humphries, D.J., Crompton, L.A., and Reynolds, C.K. 2016B. Effects of diet forage source and neutral detergent fiber content on milk production of dairy cattle and methane emissions determined using GreenFeed and respiration chamber techniques. J. Dairy Sci. 99:7904–7917. doi:10.3168/jds.2015-10759.
  9. ↑ Sebek, L.B. 2019A. Project 11: Enterisch methaan: emissievariatie in de Nederlandse melkveestapel. 1 p. Wageningen : Wageningen University & Research.
  10. ↑ Bannink, A., Spek, J.W., Dijkstra, J., and Sebek, L.B. 2018. A Tier 3 Method for Enteric Methane in Dairy Cows Applied for Fecal N Digestibility in the Ammonia Inventory. In: Front. Sust. Food Syst. 2:66.
  11. ↑ Sorg, D., Difford, G.F., Mühlbach, S., Kuhla, B., Swalve, H.H., Lassen, J., Strabel, T., and Pszczola, M. 2017. Comparison of a laser methane detector with the GreenFeed and two breath analysers for on-farm measurements of methane emissions from dairy cows. Comp. Elec. Agric. 153:285-294.
  12. ↑ Mühlbach, S., Sorg, D., Rosner, F., Kecman, J., and Swalve, H.H. 2018. Genetic analyses for CH₄ concentrations in the breath of dairy cows measured on-farm with the Laser Methane Detector. In: Proceedings of the World Congress on Genetics Applied to Livestock Production, Abstract No. 186, 11-16th February, Auckland, New Zealand.
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