According to this New Scientist article, feeding rapeseed (canola) oil to cows can produce butter with a better balance of unsaturated fats.
Apparently the proportions in the feed have to be handled delicately, as the cow’s rumen (forestomach) contains bacteria that don’t respond well to the presence of so much canola oil.
I wonder if this would have any effect on bovine methane production … one of my student groups is doing a research project on livestock methane production and greenhouse gases in the southern hemisphere. Better butter and less gas might be asking for a lot, but … strive for it!