This was one of those films that got aired in school in lieu of class on the day before a vacation break. IIRC, there was no spoken dialogue (or very little).
The story was about a young lad and his favorite horse. What was most memorable about it to me was one crucial scene - the boy goes out riding alone on a bleak, rainy day and happens to come across another horseback rider in a long tunic & hood. It turns out the rider is Death - the boy peers under the rider’s hood and sees a skeleton. Frightened, the boy rides away, but the horse has an accident, tripping & falling & getting caught in a muddy pond. There is a sequence in which a lot of men try valiantly to pull the horse out of the pond and get it back on it’s feet, but the horse is too panicked, and its’ kicking & flailing only causes it to get sucked further down into the pond, and dying. (Either it drowns or it has to be put down - I can’t remember.)
I just remember being a little traumatized by that film - the rider being revealed as the Grim Reaper was actually very scary for a first grade classroom, and the absence of dialogue and depressing downbeat ending kind of threw me. But for the life of me, I can’t remember what the title of this movie is; does it ring any bells?