THE RESEARCH COLUMN: June 2014.
by Heinz H. Meissner
On a world-wide basis, dairy animals, including cull cows and beef cattle from dairy
breeds, are estimated to contribute only 4% to anthropogenic (man-made) greenhouse
gas emissions (GHG). In many developed countries, the contribution is even less, due to
higher productivity, the dilution by emissions from other sectors and lack of significant
land use change. In South Africa we estimate the contribution of the dairy sector as no
more than 0.5%, mainly because it is a very small sector. So, why should the dairy sector
in any country be concerned about methane (CH4) emissions? Reasons advanced by Dr J.R.
Knapp and co-workers in their review in the Journal of Dairy Science, Volume 97, pages
3231 to 3261 of 2014, with the title: Enteric methane in dairy cattle production: Quantifying
the opportunities and impact of reducing emissions, are as follows: First, international
policy discussions focused on non-carbon dioxide (CO2) emissions such as CH4 and nitrous
oxide (N2O), because they are less expensive to mitigate than CO2. Often, CH4 mitigation
approaches can be economically advantageous as well as environmentally beneficial.
Second, because the CO2 emitted by livestock, including dairy cattle, arises from
metabolism of plant-derived feedstuffs, it is viewed as part of a continuous biological
cycle of fixation, utilization and exhalation. Accordingly, it is defined as biogenic CO2 and
livestock are considered to be a zero net source of CO2. Third, enteric (derived from rumen
fermentation) and manure CH4 comprise more than 40% of the GHG emissions associated
with fluid milk production. Last, some retailers and consumers in both domestic and
international markets are concerned about the contribution of GHG emissions to the
carbon footprint of foods. Another reason one can add is that the global warming
potential of CH4 and N2O is respectively 23 and 310 times that of CO2; so, it makes sense
to focus on these gases. What mitigation options do we have?
There are many opportunities to reduce enteric CH4 and other GHG emissions per unit of
product from ruminant livestock. Research over the past century in genetics, animal health,
microbiology, nutrition, and physiology has led to improvements in dairy production where
intensively managed farms have GHG emissions as low as 1 kg of CO2 equivalents (CO2e)/kg
of energy-corrected milk (ECM), compared with >7 kg of CO2e/kg of ECM in extensive
systems. In comparison, CH4 emissions in the South African dairy industry are about 1.3 to
1.6 kg CO2e/kg milk produced. Options should be introduced that have been demonstrated
to mitigate enteric CH4 emissions per unit of ECM (CH4/ECM) from dairy cattle on a
quantitative basis and in a sustained manner and to integrate approaches in genetics,
feeding and nutrition, physiology and health. Important also is that the methods employed
should sustain herd productivity, as production level and efficiency of production are two of
the most important mitigation options, and available to all farmers.
The researchers developed a nutrition model based on carbohydrate digestion to evaluate
the effect of feeding and nutrition strategies on CH4/ECM and a meta-analysis (which is a
powerful statistical tool) was conducted to quantify the effects of lipid supplementation on
CH4/ECM. The addition of a limited amount of lipids (fat) to the diet is known to reduce
enteric CH4. A second model combining herd structure dynamics and production level was
used to estimate the effect of genetic and management strategies that increase milk yield
and reduce culling on CH4/ECM. This provided the opportunity to integrate the effects of all
factors contributing to mitigation, whereas past efforts in CH4 mitigation have largely
focused on identifying and evaluating CH4 mitigation approaches based on nutrition,
feeding, and modifications of rumen function.
The results show that nutrition and feeding approaches may be able to reduce CH4/ECM by
a modest 2.5 to 15% where these are already optimal as in developed countries, but have
much larger potential in developing countries or where milk yields are still comparatively
low. Rumen modifiers such as monensin, however, have had very little success in terms of
sustained CH4 reductions without compromising milk production. More significant
reductions of 15 to 30% CH4/ECM can be achieved by combinations of genetic and
management approaches, including improvements in heat abatement, disease and fertility
management, performance-enhancing technologies, and facility design to increase feed
efficiency and life-time productivity of individual animals and herds. Genetic selection for
feed efficiency, heat tolerance, disease resistance and fertility can augment selection for
milk yield in reducing CH4/ECM with the potential of 9 to 19% reductions. Improved
management approaches such as with oestrus detection, oestrus synchronization, detection
of early embryonic death, heat stress abatement and transition cow health would result in
improved reproduction, reduced number of cows culled due to reproduction failure and
disease and a reduced replacement rate. Combined these factors can also have a reduction
effect of 9 to 19%. However, many of the approaches discussed are only partially additive
and together will not necessarily achieve the potential reduction. In addition, all approaches
to reducing enteric CH4 emissions should consider the economic impacts on farm
profitability and the relationships between enteric CH4 and other greenhouse gasses.
Bottom line: Many of the opportunities to reduce CH4 are in the grasp of every dairy
farmer and can be introduced successfully together with a consulting veterinarian,
nutritionist and geneticist. The beauty of it is that almost all measures will increase milk
production, efficiency and profitability and therefore there should be no reluctance to
initiate mitigation!