A paper from the University of Sussex that shows that horses 'understand' human emotions  has been published - a layman's version can be found on the BBC. To some degree this is probably quite well known by horse people, even taking into account that humans tend to project their emotions and anthropomorphise their pets.
While you could take the cynical, sensationalist approach by a certain UK newspaper (if you read the comments to the article then this is a crisis in the equine world brought on my left-wing, migrant, EU bureaucrats seeks to steal UK jobs and entitlements), this actually is quite fascinating research.
For a start, looking at this piece of work then it confirms a number of facts about horses, namely that being a domesticated animal they have either evolved an ability, or, used an innate ability (due to their existence as herd animals) to understand humans; in much the same way as dogs.
In a more general sense it also confirms some aspects that we've suspected about how the brain works regarding how emotions are processed. Though more interestingly while it answers some questions it opens up a whole new set of questions about how the brain works.
When reading work such as this, the experiment might be very small and limited in nature, it does open huge questions about, in this case, emotion processing in the brain, the evolution of cross-species communication, whether emotions (or certain emotions) are fundamental in nature, aspects of the human-horse relationship since early domestication etc.
 Amy Victoria Smith, Leanne Proops, Kate Grounds, Jennifer Wathan, Karen McComb (2016)
Functionally relevant responses to human facial expressions of emotion in the domestic horse (Equus caballus). Biology Letters Published 10 February 2016.DOI: 10.1098/rsbl.2015.0907