Scientists took blood samples from a mixed-breed terrier and a goat, who often played together at an animal refuge in Arkansas.
They tested the animals' oxytocin levels separately, and then put them in a pen to interact for 15 minutes, 'New York Post' reported.
The dog's oxytocin levels spiked 48 per cent, comparable to a human who is excited about a new friendship, researchers found.
"This shows that the dog was quite attached to the goat. The moderate change in oxytocin suggests the dog viewed the goat as a 'friend'," said head researcher Paul Zak from Claremont Graduate University.
The goat was even more smitten, said the researchers.
"More striking was the goat's reaction to the dog: It had a 210 per cent increase in oxytocin. We essentially found that the goat might have been in love with the dog," said Zak.
"The only time I have seen such a surge in oxytocin in humans is when someone sees their loved one, is romantically attracted to someone, or is shown an enormous kindness," Zak added.
The study concluded that domesticated pets release the hormone when interacting with other animals and humans, the report said.