I have no idea if I read them all, or how many I read. I don't remember a thing about what happens in them, plot-wise, or who the characters are. But I do know that these covers were SUPER influential on me in my early days of sim horse clubs:
I loved the white/gray pony so much (esp. w/ the pretty flower accents!) that she's either the reason I adopted a beloved similarly-colored Welsh (Kissin' Angels) at the beginning of DAA, or I modeled said pony after this one in my head. I also loved the little Jack Russel Terrier, which sparked a whole secondary side character who had a bunch of those terriers on her farm.(and the boy makes me think of Jake from Animorphs and is generally my type at that age, so I feel like I probably thought he was cute)
The the blonde girl in the hat-wearing-horse cover, her face is super familiar to me too, and I didnt' nab a picture of it here, but the little bay on cover 8 -- I borrowed him for a different sim club too. The other covers don't give me quite as strong an association, but reading through the summaries of all 10, a few of the horse names and plots ring some bells.
One that does not ring any memory bells is the plot of the first book shown here, but I WANNA READ IT LIKE YESTERDAY NOW:
Megan finds the grave of a young girl exactly her age who lived at Thistle Ridge Farm more than a hundred years ago. Some say her spirit still wanders out to the pasture to visit her beautiful white horse. At first, Megan tries to ignore her fears -- only babies believe in ghosts. But when Amanda and her horse, Prince Charming, suddenly disappear, she doesn't know if she's on the trail of the missing girl or about to come face-to-face with a restless spririt from the past!