A lot is happening between a cow's ears
The results of this important study show that "ear postures are indicative of what is suggested to be a positive, low arousal emotional state in dairy cows and could therefore be a useful, non-invasive measure of emotional state when used by trained observers."
I want to call attention to this paper because it shows it is easy to assess a cow's emotional state and that this information can be used to improve their lives. As the authors note, "Studies such as ours seek to address the lack of knowledge of positive emotions, and successful results enable animal welfare scientists to work towards ensuring a good life for animals ... Furthermore, positive treatment of dairy cows and the promotion of positive emotional states has also been shown to have beneficial effects on milk yields ..."
We owe it to these and other animals to give them the very best lives we can. And, often, it's easy to assess what they're feeling and we must use this information on their behalf.