This journal club episode comes to you from the 2024 Tri-State Dairy Nutrition Conference. The paper is “Methane in the context of circular dairy farming” from the conference proceedings.

What is circular dairy farming? The concept is that instead of extracting or using natural resources and then discarding the wastes in a linear kind of fashion, economies should try to be increasingly circular. This would include the concepts of reusing, recycling, upgrading, upcycling, etc. Traditionally, the focus on methane was about the inefficiency and leakage of energy and finding a way to minimize that from the perspective of energetic efficiency and productivity. More recently, the focus on decreasing methane has been the environment. (3:19)

Dr. Newbold talks about the trade-off between circularity and methane. High fiber diets produce more methane than high starch diets. Adding fat to diets can also decrease methane production. However, starch and fat are human edible so if we leave starch and fat in feeds to decrease methane in dairy cattle, that leaves less starch and fat for human consumption. The concept of “local” also plays into circularity, whether that be feed production or milk processing. (7:01)

What are the metrics of circularity? Two approaches to this present in the literature. The first is  human edible efficiency: how much human edible food are we producing? In a dairy setting, the measurement would be how much human edible food are we putting into the cow compared to the amount of human edible food coming out of the system? The second metric is the alternatives for land use. (10:45)

What is the best way to express methane production? Dr. Newbold shares three, and they are generally used in different contexts. First is methane production, usually presented as grams per cow per day. This is an easily scalable measurement, but may not be the best or easiest way to manage interventions on-farm. The second common metric is methane yield which is generally expressed as grams per kilogram of dry matter intake. Lastly, methane emissions intensity is grams of methane per kilogram of milk. (12:26)

When considering the human edibility equation, the denominator consists of the human edible content of the feed. In principle, depending on how hard you worked and how much money you spent, you could extract some of the starch, fat, and protein and use it for human food. However, there's no consensus in the literature about this kind of edibility coefficient. In other words, what proportion of the protein in soybean meal or the proportion of starch that's left in wheat middlings or distillers grains is human edible? Greater consensus about what is and what is not human edible would actually be quite useful in allowing for better and more consistent calculations. (18:29)

Dr. Newbold gives examples of relative efficiency comparing U.S. dairy production, a grass-based system, and a tropical grass based system. Each of these have a different human edible efficiency and a different amount of methane produced. (19:59)

When it comes to lowering the environmental impact of milk production, don't focus on one metric in isolation of the rest of them. If you're setting off in a particular direction, whether that's trying to drive methane down or milk production up, think about the potential trade offs and unforeseen consequences. (32:12)

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