Krista McLennan, who made the discovery while working on her PhD at Northampton University, believes her findings could help improve milk yields.
In her study, the 27-year-old measured the heart rates and cortisol levels of cows to see how they cope when isolated.
Cattle were penned on their own, with their best friend or with another cow they did not know for 30 minutes and their heart rates were measured at 15-second intervals.
The research showed cows were very social animals which often formed close bonds with friends in their herd, the `Daily Mail` reported.
She said: "When heifers have their preferred partner with them, their stress levels in terms of their heart rates are reduced compared with if they`re with a random individual.
"If we can encourage farmers to keep an eye out for those cows which like to keep their friends with them, it could have some real benefits, such as improving their milk yields and reducing stress for the animals, which is very important for their welfare.
"I`ve spoken to a number of farmers who have said they do notice bonds building among their cows and some spending a lot of time together."
McLennan pointed out that modern farming practices mean cows are often separated for visits from the vet or by farmers moving their stock around.
"We know re-grouping cows is a problem, because there`s a high level of stress among animals as they try to integrate into a new group," she said.