Cows don't "already eat parts of cows" except in that most tenuous sense you made out of self reabsorbtion of placenta, which is common to mammals.
Do I "eat parts of people" if I chew on my nails? In the same tenuous sense I do "eat parts of people", but really we both know - its just a stretched caveat to the rule that we dont really eat people, and cows dont really eat cows.
And what kind of "small animals" do cows hunt ? Slugs, beetles perhaps... never mind.
Cows will eat chickens, mice, baby birds; basically what they can get. Same goes for deer. Pretty much any animal will opportunistically eat any food that's more calorically dense than their typical diet.
That's nonsense. Herbivores will not "eat any food thats more calorically..." they eat what they have specialised to eat. Some even just eat one species of plant. Where do you find cows that hunt chickens and mice or chickens and mice that willingly sacrifice themselves to cows?
And this is all a fools errand away from the idea of cannibalistic cows!
I get they can - on rare occasion. I'm indignant about the stretch of language, presenting "can" and "sometimes" as "will" and "do", and the way this was tacked onto placenta eating to help say they "already eat parts of cows". To me this is all plain argument through exaggeration.
Herbivores don't need to eat meats and do so rarely, it has hardly been noticed. Sure, some slugs and insects may be an expected nutritional boost and help the digestive system cope with more, on rare occasion. But feeding cows cows does result in prion disease similar to other mammals, like humans suffer from the vanishingly rare practice.
So the actual news would be if cows could survive deformed protein.