"anytime a cow eats fresh grass, it creates cream high in conjugated linoleic acid, a heart-healthy unsaturated fat that’s liquid at room temperature. In cream from animals fed grain, however, saturated fats dominate, which makes for a stiffer, more brittle butter."
Recall reading a paper on the subject - the composition of milk between American and European cows is noticeably different.
Possibly this
[0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3475924/