What was done
If one feels strongly about the (debatable) need to reduce greenhouse-gas emissions to the atmosphere, a good place to start is with the next most important greenhouse gas after carbon dioxide, i.e., methane (CH4), each molecule of which has a global warming potential about 21 times greater than that of a CO2 molecule.  Within this context, Boadi et al. review what is known about both established and newer methods for reducing CH4 emissions from dairy cows.

What was learned
The authors report that existing mitigation strategies for reducing CH4 emissions from dairy cows include the addition of ionophores and fats to their food, as well as the use of high-quality forages and grains in their diet, while newer mitigation strategies include "the addition of probiotics, acetogens, bacteriocins, archaeal viruses, organic acids, [and] plant extracts (e.g., essential oils) to the diet, as well as immunization, and genetic selection of cows."  In fact, they provide a table of 20 such strategies, where the average maximum potential CH4 reduction that may result from the implementation of each strategy is 30% or more.

What it means
With as many as 20 different mitigation strategies from which to choose, each one of which (on average) has the potential to reduce CH4 emissions from dairy cows by as much as a third, it would appear there is a tremendous potential to dramatically curtail the amount of CH4 released to the atmosphere by these ruminants and, by implication, the host of other ruminants that mankind raises and uses for various purposes around the world.  Such high-efficiency approaches to reducing the strength of the atmosphere's greenhouse effect, while not reducing the biological benefits of elevated atmospheric CO2 concentrations in the process, should be at the top of any program designed to achieve that difficult (but still highly questionable) objective.