I watched it last night and (as usual with anything to do with horses) I cried!
I was a little 
over Luca Cumani's suggestion that horses race because they are scared. Yes racing taps into the primeval instinct that tells a horse to run, but the horses are not scared per se.
I wonder if something got lost in translation as Luca is Italian (and a bit of a git by all accounts).
I work in racing btw.
Looking forward to part 2.