A study conducted by the Mammal Vocal Communication and Cognition unit of the University of Sussex in the United Kingdom has found young horses under the age of three are not able to understand when a human is paying attention to them. Adult horses, however are able to use head movement and open or closed eyes to understand when a human is paying attention to them. The results of this study suggest the ability for horses to read and understand human body language is a skill that develops over time and with experience.
We've seen and/or heard what happens when a foal is raised by a human and doesn't understand horse body language. The horse thinks s/he is a human and not a horse and cannot function at all in horse society. This makes me wonder if all body language, regardless of the species, is a learnt behavior for horses?
If this is true, then imagine how powerful it is for the young horse when first learning both horse and human body language. This means the teacher, both horse and human, must be very skilled in his or her teaching abilities and truly understand all aspects and nuances of horse and human body language.
Something to consider when turning out your foal with older horses and planning his/her training, whether you place him/her with a trainer or do it yourself.