By George Harvey
Conventional wisdom on beef and dairy products is that they are responsible for a large part of our greenhouse gas emissions. The issue of how to deal with that is not without its controversies, and there is still a lot of work to be done on understanding the highly complex science involved. One thing that scientists agree on, however, is that cows belch up a lot of methane, typically 70 to 120 kilograms, 164 to 264 pounds, per year, each.
Please pardon little math. Methane is about 25 times as powerful as carbon dioxide in its greenhouse gas effects, so 264 pounds of methane is the equivalent of 6,600 pounds of CO2. That is the amount produced by burning 300 gallons of gasoline. So the annual production of greenhouse gas emissions from one heavily productive cow can be compared to driving 15,000 miles in a Prius that gets about 50 miles per gallon.
The problem is of methane emissions common to all ruminants, including cattle, goats, sheep, deer, and others. These animals have stomachs that are divided into four chambers. In the first of these chambers, microbes break down the cellulose in plants, which are otherwise largely indigestable, producing by-products that the animals can digest and use for food. The problem is that one important by-product has no use to the cow, and it is methane.
Recently, NBC released a video, “Cow farts and climate change” (http://bit.ly/bovine-gas). It tells the story of research done on the diets given to cows and how much methane is released. One statement in the video really caught our attention. It was, “Even small amounts of dried seaweed, introduced into a cow’s diet, can cut methane gas by as much as 99%.”
We called Dr. André Brito, Associate Professor of Dairy Cattle Nutrition and Management, at the University of New Hampshire, who had been interviewed for the video. He made it clear that, while the video was factual, it did not tell the whole story.
Dried seaweed is commonly added to the diets of cattle for reasons that have nothing to do with methane emissions. The seaweed is beneficial to the health of the cattle. One survey Dr. Brito talked about had responses from about 30% of the 1000 farmers surveyed. Of these, upwards of half provided seaweed to the cattle.
Results from experiments looking at the effects of seaweed on methane emissions varied widely. One experiment done in New Hampshire, using the locally available algae fed to cattle, looked at the amount of methane produced, and did not find any reduction. A second experiment did find a small but significant reduction in the activity of methane-generating microbes.
Another study, done in Australia with a different species of algae, produced very different results. It used a species of red algae called Asparagopsis taxiformis for in vitro experiments to determine the effects of varying percentages in the feed on the amounts of methane emitted. It is from this study that the video got its information that a small amount of dried seaweed could cut methane production by 99%. We need to emphasize that this work was done in vitro, meaning “in glass” (e.g., in a test tube), and not in an actual cow.
We might note parenthetically that Asparagopsis taxiformis is a commonly-available seaweed in tropical areas and is used as part of a human diet. In fact, it is used as a condiment in Hawaiian cuisine, known as “limu kohu,” which is Hawaiian for “pleasing seaweed.”
The highly variable results of experiments can be attributed in part to the fact that research on how diet affects the methane production of cattle is just in its beginning stages. Clearly, it is possible that different species of algae will have very different effects on the amounts of methane produced. Just how effective mitigations can be, what species to use, what amounts to use are only parts of a larger puzzle whose answers are yet to come.
We do not have the final answers, and we can only leave finding them to science. We hope that science will produce valuable results.