Today someone posted this question and comment on one of my favorite message boards:
I wonder if horses can be like other animals that react negatively when we go away, but in [my horse's] case, it would more likely be that I had those other people ride her AND I went away for a couple days.
Yes, horses can act out and hold a grudge. I don't see it often, but I do know a few how consistently give their owners the "cold shoulder" or act out when they feel that their owners are absent from the usual routine. From a human perspective, it's nice to be needed, but it's not practical that a horse gets pissed when they aren't tucked in every night.
Like the horse owner above, I would be more inclined to consider in whose care I left my horse.
My husband and I used to have three cats. We always imposed upon friends to handle the cat duties when we went on trips. You could tell when the cat sitter spent a little time with them, because we'd come through the door and they be in their comfy perches or nooks and look up to acknowledge our return, the cat equivalent of a casual, "Yo, whassup." After one trip, when I left my best friend in charge (he's not an animal person), the oldest cat charged to the door as we came in, as if to say, "Where the heck have you guys been... you don't know what's it's been like... etc." That night, he peed on me in bed, right on the spot he usually sleeps. That is very un-cat-like behavior, so we got the message.
The point of the cat story is that animals have better rapports with some people than the others. When I ride other people's horses, I really try to take the time to make sure they are relaxed and happy. That's not always possible with a nervous horse that I seldom ride, but, in that case, I will do simple ground work, even something as basic as backing them in hand, to get it in their heads that I can put pressure on them, they can respond, and there's a release at the end of a proper response in other words, I demonstrate that I will try to communicate with them in a way in which they can understand. If I still have a guarded horse on my hands, I can also reach into my equine massage toolkit to soften them a little physically and mentally. My goal, by the end, is to give the horse exercise and to have them licking and chewing and interacting with me. I'll never be a fabulous rider I started much too late in life but I can gain their respect and make them comfortable when they're around me.
It took me a long time to find someone who has a similar approach so that I could leave my EPM OTTB, Jazz, for several days. Many of the pros at my barn that are effective riders are either unforgiving and inflexible or are past middle-age and can't afford to ride predictably unpredictable horses. Jazz has improved somewhat in the past couple of years, so, in the near future, I plan on trying other riders on him, but in a controlled environment, not when I'm out of town.