My Friend Flicka, Thunerhead. The Jill books of course. Silver Snaffles by Somebody ( think it might be Rosemary) Cummings (my favourite). Black Beauty of course and Silver Brumby.
The Usborne Guide to Riding and Pony Care. Not sure of the date as it's in a box atm - I would have acquired it in the early 90s but I'm sure it's early 80s at least. The pictures suggest possibly 70s.
Johanna Cannan Jean books are probably my oldest. Early 1940s I believe. I also have almost all Pullien-Thompson's, Gillian Baxter, "Jill" books, My Friend Flicker, among others Most date from around 1950 to 1970.
I have quite a few old books, some not as old, one of the most read was my little horse breeds book, I loved looking through it for hours and reading up about all the breeds so usually I am quite good at knowing what breed a horse is, please don't test me though lol
I also have (though sadly got rid of most when I moved) Welsh Pony & Cob Society Manuals, used to love reading up about all the welsh cobs, we were members as we used to breed them years ago
Got various others such as foal to five years, a-z veterinary book, horse massage, etc
The Young Rider, loved that book, it had a photo of a girl called Fiona Forbes on a dun pony called Babysham on the cover. I still have a copy of Silver Snaffles, wonderful illustrations.
Got lots of non fiction books from when I was a kid and some fiction books my mum gave me including a great one called "Finding our stirrups" by J Kinnard.
Also love The Saddle Club!