Farmers score no points with their dairy cows for whispering sweet nothings in their ears, animal researchers say.
Given a choice, only food can keep the animals happy, according to animal behaviour scientist Edmond Pajor of Purdue University in Illinois.
An anxious cow produces up to 15 per cent less milk -but farmers know little about what troubles them, Mr Pajor told this week's Nature science journal.
The researchers put dairy cows into a Y-shaped maze. The animals walked towards one of two people at the end of the plywood corridors offering food, a scolding or a stroke.
The experiment showed that to the sensitive beasts, shouting was as nasty as a smack or an electric cattle prod. But they were oblivious to a caress or gentle voice and obsessed with food over everything.
The moral of the story for farmers is to think about how they deal with their herd, Mr Pajor says. But "you don't necessarily need to go over the top and pet them".