Managing methane through nutrition

Annually, the U.S.’s total greenhouse gas (GHG) footprint is about 6.3 billion metric tons of carbon dioxide equivalents, a unit of measurement that is used to standardize the climate effects of various GHGs. According to Kirby Krogstad, assistant professor of dairy nutrition at Ohio State, agriculture accounts for about 10% of that total. Within that 10%, the dairy industry is responsible for about 139 million metric tons – 2%. That percentage seems low to many dairy farmers. So low, they often wonder if the industry is being singled out for its GHG emissions. Krogstad, however, likes to put the statistics into context. “If the U.S. dairy industry were a country all its own, and there’s something like 205 countries in the world, the U.S. dairy industry would rank 49 out of that 200 in total carbon dioxide emissions,” said Krogstad. “The United States dairy industry has a larger carbon footprint than whole countries – Sweden, Norway, Israel, New Zealand and Finland. I do think we have a responsibility to continue working to reduce that footprint and increase our efficiency.” Can Increasing Starch Help Reduce GHGs? Feeding extra starch is one way to reduce methane emission in dairy cows. Krogstad cited a study in which cows were fed four different starch diets, 10% through 40%. This was achieved by increasing corn grain and reducing soy hulls. To achieve the 40% starch diet, some of the forage needed to be removed to make room for all the corn. In terms of milk production, there was a positive linear response as the starch was increased up until the 30% starch diet. Milk production then began to drop back down with the 40% starch diet. As expected, methane levels dropped as starch was increased. The 40% starch diet saw a 14% reduction in enteric methane emissions. The tradeoff to increasing starch is a reduction in milkfat. There is also a risk for acidosis. For this reason, Krogstad doesn’t think that increasing starch is a strategy for meaningful GHG reductions. “But maybe increasing starch a little bit in diets here and there might get us a little smaller methane footprint around the margin,” he said. What About Increasing Fats? Krogstad noted a recent Canadian study where researchers supplemented three rations with either crushed sunflower, flax or canola. The addition of the oilseeds reduced methane emissions by 10% - 18%. Feeding polyunsaturated fats (of which flax is the highest of the three) as opposed to monounsaturated fats resulted in the higher percentages. Milk production did not change with the addition of the oilseeds. Krogstad also said that fats have potential health and reproductive benefits, especially the polyunsaturated fats which can improve cyclicity and may reduce inflammation. Like with the starch, there was a tradeoff: when polyunsaturated fats are increased in the diet, milkfat decreases. Neutral detergent fiber digestibility also decreased, meaning that the animals weren’t utilizing the feed material as well. Oilseeds are also expensive. “You’ll need to decide whether the costs of these fats are worth the potential risk in milkfat depression and reduction in fiber digestibility,” Krogstad said. What About Feed Additives? A mid-2000s study found that feeding Rumensin® reduced methane emissions by 5%. The study also showed a reduction in feed intake and an increase in milk yield. According to Krogstad, Rumensin generally has a good return on investment with the current predicted responses. Another feed additive is Bovaer®. “This is kind of the new shiny star of the feed additive class for methane mitigation,” said Krogstad. Studies from Penn State and UC-Davis showed that Bovaer demonstrated a 30% reduction in methane emissions with no effect on protein, a slight increase in milk yield and an increase in milkfat. Essential oils are a third additive choice. There are over 3,000 individual molecules that can be characterized as essential oils, so Krogstad said it’s impossible to make broad sweeping characterizations. Agolin is one essential oil that has been studied. While one 2020 study found that agolin reduced methane emissions by 9%, a more recent 2023 paper found no change in methane when using it. All three of these additives currently have a carbon project associated with them, so farmers feeding them can get paid for the credits they are generating. Krogstad encouraged dairy farmers to use two return on investment calculators to experiment with how feeding these additives could impact their herd and finances. The first is fairly simple; the second requires more data input: The Dairy Carbon Return Calculator 2.0 Excel spreadsheet (at tinyurl.com/mr42tkmz) The AgNext Feed Additive Calculator Tool (FACT) for Dairy (at agnext.colostate.edu/dairy-fact) “For any of these additives that are continuing to come to market, make sure to ask for independent and peer-reviewed research, so you can determine how confident you are in that product’s effect on your cattle. Any of these options, to a degree, will have trade-offs,” Krogstad cautioned. by Sonja Heyck-Merlin