The college textbooks are by far the best things to have on hand, in my opinion. There aren't any vet schools near me so I have to buy them from barnes and noble.com or amazon.com. At barnes and noble.com, if you go to college textbooks and put in equine in the search box, you'll get tons of interesting books.
On the other hand, if you like to read anecdotes along with the vet care, "The Horse Doctor Is In" is a really good read. Lots of information on horse health care but he discusses his real life cases with clients and horses and it's really interesting to read. It's not full of technical jargon that you need a vet dictionary to understand, it's all in layman's terms. It's one of my favorite books. Author is Brent Kelley, DVM.
You had also mentioned one called "Horse Owner's Veterinary Handbook" and posted a picture of it. I have that one and it's been very helpful.
A lot of the text books are available at www.Powells.com used (they are pretty expensive new).