This was the first in the series that I read (out of order) ... I've read Seabiscuit, and seen that movie and many other horse racing movies, have read lots of books set in the depression era. It all felt familiar. Nice to have this information set in a story for a younger audience. Gelding is mentioned but not explained (Mommy, what does it mean to "geld" a horse?) There is some animal endangerment (not quite abuse, although overuse could be argued as that). I wasn't actually sure where this story was going to go, it kept me guessing. 

I was shopping a library sale and picked up several of these HorseDiaries books (for my Little Free Library). During my "MiddleGrade May" I figured I'd give a couple a read myself. I think I would have liked these a lot in my younger years, and I would give them a thumbs up to any young reader. My 4* rating is more a "for kids" rating rather than my own adult enjoyment (more of a 3* in that regard).

Very easy, anthropomorphized ... as the series title suggests, these are basically the horses thoughts, although not written in diary format (just a telling of their life). There are 16+ books in the series, all stand-alones, set in various times/places. So readers are learning about history, as well as horses. They don't need to be read in order. Several authors/illustrators.

I really hope children(and any adults reading) would continue to read the appendix after the story ends. Here, there are the author's notes, more about the history, and horse breed, given factually, giving the background on the fictional story. Good info!

No audio, but I was able to find a Kindle copy at my library in addition to the physical books I picked up.