I agree, we need to slowly study other groups of cows to see if this is a viable solution.
I'm reading Factfulness by Hans Rosling at the moment. He had a great point about "single numbers" - the jist was to always be skeptical of just a single number or metric.
Here's an example [1]. During WWII, soliders were dying in their own vomit because they were laying prone on the battlefield, in sick beds, etc and left unattended. Doctors tried using the Recovery Position [2] and saw a decrease in those types of deaths by about 99% (this is in the book).
Sounds like it should work for other types of people, right? First aid organizations quickly updated their "best recommendations" for all types of people: sick, drunk, young, old. This position was the best possible position for increased airway access, thereby decreasing preventable patient deaths.
It wasn't until the 1980's that this idea was challenged. A few health organizations noticed an increase in infant deaths. Hong Kong's group was the first to investigate this [3]. Other groups joined in and realized that infants, when turned on their stomach, do not have the strength to tip their heads after they vomit. As a result, infant deaths increase when they are placed into the Recovery Position.
The recommendation was quickly updated in the late 1980's / early 1990's. Now the recovery position is recommended for people ages 5 and up.
Between 1940 - 1985, there was a larger number of infant deaths because one group of well-meaning people took some knowledge they gained for one group and quickly applied it to all other groups.
I think this study (cows reducing methane based on diet) is a great idea. But we need to be cautious about applying this quickly to all cows, else we could kill half the cow population and cause the cost of beef to skyrocket.
[1]: https://www.gapminder.org/factfulness-book/notes/, Page 163.
[2]: https://en.wikipedia.org/wiki/Recovery_position
[3]: https://www.ncbi.nlm.nih.gov/pubmed/2866397?dopt=Abstract