Most herbivores are actually able to eat meat; they just generally don't because it's easier to get access to plants. They have super powerful stomachs that can consume fibre way more easily than carnivore stomachs can, so they generally have no trouble at all with the relatively-easy-to-digest meat that carnivores eat. https://www.smithsonianmag.com/smart-news/when-herbivores-arent-poor-chicken-got-eaten-cow-180951115/ is an article that explains much more about it.
Now, this brings us to the obvious question of whether cows would be able to eat a lion. As far as I'm aware, they should be able to - lions don't produce any poison or venom, and they don't need any defence mechanisms like being inedible, because they are apex predators. So, assuming the five cows found an already-dead lion, they should have no trouble at all eating the lion - if you've ever seen a bull, then you might find it rather easy to believe that five bulls could easily kill a lion.