This journal club episode comes to you from the 2024 Tri-State Dairy Nutrition Conference. The paper is “Practical Aspects of Reducing Carbon Footprint by Dairy Farms Through Feeding” from the conference proceedings.In the U.S., livestock competes with oil and gas for the top source of methane emissions. While “carbon-neutral” agriculture may be easy for modelers to show, Dr. Hristov feels this is misleading and probably impossible in practical dairy farming. However, mitigation can be addressed in several directions, and nutrition can have perhaps the largest impact. Management practices, genetic selection, and manure management can be added to achieve large reductions in total methane from an intensive dairy production system. (2:43)As forage digestibility increases, methane yield and intensity will decrease. A forage with higher digestibility may gain a 10-15% improvement in methane intensity compared to a lower digestible forage. In addition, starch makes less methane than NDF does. Feedlot cattle produce half the methane of a normal dairy cow due to the increased starch in the feedlot diet. We know fats and lipids can decrease methane, but anything higher than 5-6% in the diet will disturb rumen function and lead to poorer performance. Comparing different forages, corn silage produces the least methane, with alfalfa in second place. (6:41)Feed additives have the potential to deliver compounds for methane mitigation. One of these is 3-nitrooxypropanol (3-NOP), the commercial version of which was developed in Europe. It is approved in Europe and Latin American countries. Australia and New Zealand are also working through the approval process. This compound inhibits the MCR enzyme (methyl coenzyme M reductase) which catalyzes the last step in methanogenesis. Dr. Hristov’s lab has consistently shown a 30% reduction in methane yield when diets containing 3-NOP are fed, with no impact on milk production and a slight increase in milk fat. 3-NOP is quickly metabolized, so it is most useful in a confinement system where it can continuously enter the rumen. The compound is stable in a TMR for up to 24 hours, and the optimum inclusion rate is 60-80 milligrams per kilogram of diet (60-80 ppm). (14:41)Regarding regulatory approval in the U.S., the FDA has indicated that 3-NOP must be approved as a drug, not as a feed additive. Dr. Hristov has concerns about an adaptation of the cows to the compound. One study in Holland fed 3-NOP for a year, and there was a definite decrease in efficacy over time. Furthermore, efficacy may depend on diet, as 3-NOP is less effective with high NDF diets. It’s unclear if the decrease in efficacy over time is because the microbes break down 3-NOP before it affects methane synthesis or if the microbes shift to a different pathway of methane synthesis. (22:04)Bromoform, a compound found in red seaweeds, is also a powerful methane mitigator. Dr. Hristov’s lab has observed 60-65% decreases in methane production early in the feeding period, dropping to 20-25% after 200 days. Other issues include the practicality of growing and transporting seaweed, the instability of bromoform, and the fact that bromoform is an ozone-depleting compound and a carcinogen. Seaweed extracts tend to decrease dry matter intake, and thus milk production and milk iodine increase dramatically. (25:54)In the U.S. dairy system, where manure is usually handled as a liquid, methane emissions from manure and from the cow are equal. Methane digesters and flaring of methane are common mitigation methods. Acidification is another method whereby decreasing pH can decrease methane emissions and ammonia and nitrous oxide losses. Dr. Hristov predicts a lot of additives to decrease methane emissions from manure will eventually be available on the market. (31:16)3-NOP has little effect on rumen dynamics but may increase butyrate. Dr. Weiss asks if different feed additives have synergistic effects, and Dr. Hristov thinks much more work is needed in t