Yes, it is true that cows have best friends and can become stressed when separated from them. Cows are social animals that form strong bonds with their herd mates, and these bonds can be similar to what humans consider as friendship.

Research studies have shown that cows display signs of distress when they are separated from their preferred companions. For example, a study conducted by Krista McLennan, a PhD student at Northampton University, found that cows become more stressed and show higher levels of anxiety when they are separated from their best friends.

In the study, cows were paired with a companion and then separated for a short period of time. The researchers observed that the cows became visibly agitated, vocalized more, and showed signs of increased heart rate and cortisol levels, which are indicators of stress.

Furthermore, cows also demonstrate their preference for specific companions through their behavior. They tend to spend more time together, groom each other, and engage in playful activities. These behaviors indicate a strong social bond and a level of companionship that can be compared to human friendships.

While the concept of cow friendships may seem surprising to some, it highlights the complex social nature of these animals. Cows, like many other herd animals, rely on social interactions for their well-being and overall mental health.

References:

1. McLennan, K. M., et al. (2016). Friendships between cows are observable and important to animal welfare. Applied Animal Behaviour Science, 181, 19-26.
2. Webster, J. (2017). Understanding the Behavior and Improving the Welfare of Dairy Cattle. In Dairy Cattle Science (pp. 67-84). Woodhead Publishing.