On the way up to where my horses live, there are two ponies in a small paddock. They have been there for the 9 years that I've been there, and I know they don't go out. I've always felt a bit sorry for them, imagining they have a rather dull life. But actually, although I could not say for sure that they are 'happy', they certainly show no signs of discontent, and are progressing into a healthy old age.
So, I was thinking about them the other day when I was talking to someone who was feeling guilty about not getting her horse out much, as she had read that feral horses can cover large areas every day, while her pony was stuck in a comparatively small paddock. Her pony has company, ad lib hay and grazing, and 24/7 turnout.
It seems to me that we often confuse two things - giving our horses a natural life, and giving them an 'enjoyable' life. There is a big overlap between the two but they are not the same thing.
For example, if we observe a population of feral horses, and all of them travel at least 8 miles a day, it doesn't actually tell us anything about whether they enjoy doing this! If someone had observed me 2 winters ago, they would have seen me walking to visit my horses, about 1 mile through deep snow, every day - if they then concluded that I enjoyed this and arranged life for me so that I could do it every day, I'd be distinctly unimpressed - I did it because I had to :-)
Likewise, horses may travel to find water, good grazing, protection from the weather or from flies. They may also do this because they enjoy it, but we shouldn't assume so. We can think about what is physically or mentally good for them, what is natural, and what is enjoyable - all different things and some fairly impossible to measure! I'm pretty certain that many horses do enjoy wandering far and wide, but I also think that some would be perfectly content to do the equine equivalent of staying home and watching TV.
Yet again, it is down to assessing the individual, and trying not to make assumptions, whether they are based on traditional horse management methods, natural behaviour, or human preferences. There is a baseline from which, I feel, you should always start - that horses need adequate turnout, equine company, and lots of forage, but beyond that the ways in which we can enrich our horse's lives are many and varied, and very individual.
So, who knows what makes a horse happy? Your horse knows, and if you listen to him you may find out too :-)
(with no apology for using the apparently anthropomorphic term 'happy' - more on that later...)