Livestock produce a lot of greenhouse gases, but one of the most famous emitters is the cow, which “produce 250 to 500 L of methane per day” (Johnson and Johnson). Methane is an extremely potent GHG with a warming potential well beyond CO2, leading environmental advocates to seek alternatives. Some consumers choose to avoid beef while others study ways to curb cows’ emissions, like feeding cows seaweed.

The reason cows produce so much methane to begin with is that they’re ruminants, which are animals with a four-compartment stomach full of microbes that ferment their feed. However, different cows can have different microbiomes, which vary in the amounts of methane they produce. As a result, cow breeders have looked for patterns associated with lower methane emissions. 

The University of Pennsylvania contrasted qualities in cattle producing low and high quantities of methane, with the high emitting group generating 22% more methane than the low emitting group. Both groups ate the same amount and produced the same amount of milk with the same qualities, but low emitters digested less of their food and differed dramatically in their microbiomes. The fermentation pathways in high emitters “leads to higher hydrogen production, so there’s more acetate which supports elevated methane formation,” according to Dipti Pitta, one of the researchers on the project. Analyzing gene expression found less methyl-CoM reductase in low emitters, an enzyme involved in methane production. 

Size plays a factor, too. Smaller cows tend to emit less, as their rumen is smaller, which leads to a faster rate of digestion, which is unfavorable to methanogens. The reason that smaller cows produce less methane, yet maintain milk yield and quality, is because they are more energy efficient. Methane is a byproduct in cows, so cows that emit less methane can use that resource instead of emitting it as waste. The next step is investigating how cows can be bred or engineered to optimize their microbial composition for reduced methane waste, which can also be combined with other strategies.

Instead of changing the cow itself, some research has been dedicated to changing their feed, such as adding methane inhibitors or genetic engineering crops, as seen in High Metabolisable Energy (HME) ryegrass. HME ryegrass has two modified genes: one to increase the amount of oils it produces and one to stabilize the oil. Greater oil content is desirable for decreasing methane emissions, as “for every 1% increase in dietary fats that a ruminant consumes [typically results in] a 5% reduction in methane that they create.” AgResearch is also working on High Condensed Tanins (HiCT) white clover, which is also edited to provide nutritional benefit whilst decreasing methane emissions. In addition to methane reduction, HiCT white clover is predicted to increase milk and meat yield, reduce bloat, and manage pests.

I feel like it’s important to note that the citation in the first sentence, which credits Johnson and Johnson, does not refer to the health company Johnson & Johnson. The paper I cited is just written by two authors with the last name Johnson. I’m not sure of their relation, but they’ve published multiple papers together, with one including a third Johnson (Maintenance energy requirement of llamas)! It’s not all that out of the ordinary, especially with the surname Johnson, but I thought I should make an acknowledgement due to the similarity to the company name.

I was really impressed by AgResearch’s work, especially their emphasis on thorough research. Their page on HME ryegrass included cautions like “[i]t’s important to stress that the forecast environmental benefits associated with the grass need to be supported by rigorous research,” followed by an explanation of why their trials need to be repeated in New Zealand before seeking approval in the country.

I was definitely surprised to find that the cows emitting the least were also the most efficient. I guess it makes sense; the ones leaking fuel are missing out, but it’s kind of convenient that solving this problem also results in more efficient cattle! Stay tuned to learn with me!

Cows’ daily emissions: https://pubmed.ncbi.nlm.nih.gov/8567486/ 

Variations in methane between cows: https://www.vet.upenn.edu/about/news-room/news-stories/news-story-detail/could-we-breed-cows-that-emit-less-methane 

HME ryegrass: https://www.youtube.com/watch?v=OLZUVddu78U

https://www.agresearch.co.nz/news/hme-ryegrass-making-steady-progress/

HiCT white clover: https://www.agresearch.co.nz/our-research/high/source connections: https://geneticliteracyproject.org/2019/11/12/fighting-climate-change-with-gene-editing-can-we-slash-cows-methane-production/