FYI: "Feeding cows seaweed cuts 99% of greenhouse gas emissions from their burps, research finds" https://www.independent.co.uk/environment/cows-seaweed-metha...
Not OP, but when I personally talk on reducing meat consumption for environmental reasons - I do not have animal farts and burps in mind. The process of growing meat requires a lot of resources by itself and at current human population scales we are wasting vast amounts of resources (energy, land, etc.) to grow meat instead of spending those resources to feed ourselves. https://en.wikipedia.org/wiki/Ecological_efficiency#Ten_perc...
IMO, feeding animals unusual foods won't solve the main issue and produce more challenges. It's anecdata (cannot cite anyone), but as much as I've read about ecological farming, problems with animal health and infamous though prevalent use of antibiotics in industrial animal farming is due to the diets of the animals. Animals grown in ecological open farms with habitats natural for the animal grow healthier. But as mentioned in first paragraph - at current human population scales - meat consumption must be reduced rapidly.
P.S. I will digress, but as the problem is insanely big human population (and it's exponential growth), it would be great if people globally won't procreate at such rates.
A much simpler and less crazy solution is simply to have more grass-fed beef. Their manure and body shade can help recreate green pastures in desertic regions, and this would be pretty much CO2-neutral. It's just more expensive, so nobody does it.
Solutions are here, and they're not that hard. People just don't want to implement them because it impacts their profits and abilities to eat tasteless meat 3 times a day for next to nothing.
Uncontrolled innovation may have unexpected results.