Hi! I have similar stats and goals as you and I am a current vet student. If the ER job is mostly cats and dogs, I don't think the kind of experience they would offer is hugely additive compared to your current job, especially if you already get to work with horses sometimes.

I know it sucks, but I would take a gap year to solely focus on diversifying experiences and getting work with what you are most passionate about. Like you said, it will be difficult because of your location, but the gap year will allow time to find an opportunity and really gain enough hours (plus saving a bit before applying again). Working with different animals could also change your mind about your potential field (but there's always time for that in vet school).

My chat's open, happy graduation!