Cows form close friendships and become stressed when separated from their best friends.
Why it is true
Animal behaviour studies have shown that cows create strong social bonds with specific companions. When separated, their cortisol levels rise and their heart rate increases. Keeping social groups stable improves milk production and reduces stress in barns.
Source: University of Bristol
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.