From the studies I can Google, the jury still seems to be out on the dominated trans fat in animal sources, vaccenic acid, and related compounds known as conjugated linoleic acids. The later group of trans fats actually might be beneficial to human health: some studies have linked it to anti-cancer properties (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4964663/) and fat loss (http://ajcn.nutrition.org/content/85/5/1203.long), although as indicated studies are very preliminary at the moment, so you really can't conclude anything definitely about this.
I can even Google papers such as this -- https://www.ncbi.nlm.nih.gov/pubmed/19935865 -- that seem to say vaccenic acid might not be that bad, which is contrary to the link you provided. Again -- this is more not to say vaccenic acid is good, and more that I believe the science is inconclusive right now.
Elaidic acid (the "bad" partially hydrogenated vegetable oil trans fat) is present in natural sources as well, but in much smaller quantities.
Small amounts of trans fats are pretty much found in any animal product, so it is difficult to avoid trans fats entirely unless you become completely vegan. Personally... my guess is that a small amount of animal based trans fat is not going to be a big deal overall, so a little butter is fine. The studies are most damning at the moment over partially hydrogenated vegetable oil.
I can even Google papers such as this -- https://www.ncbi.nlm.nih.gov/pubmed/19935865 -- that seem to say vaccenic acid might not be that bad, which is contrary to the link you provided. Again -- this is more not to say vaccenic acid is good, and more that I believe the science is inconclusive right now.
Elaidic acid (the "bad" partially hydrogenated vegetable oil trans fat) is present in natural sources as well, but in much smaller quantities.
Small amounts of trans fats are pretty much found in any animal product, so it is difficult to avoid trans fats entirely unless you become completely vegan. Personally... my guess is that a small amount of animal based trans fat is not going to be a big deal overall, so a little butter is fine. The studies are most damning at the moment over partially hydrogenated vegetable oil.