I have to raise my hand and admit to this. When I saw the title of your post I laughed and went 'i wonder if horses count' and then I read the post and suddenly wasn't laughing at all.
I hoard horses. And it started really small.
I had one horses, and was shopping around for a second for my daughter. People I spoke to spoke to other people, and then I got a call from a girl I knew from college who knew someone who knew someone else who was looking to get rid of a horse. She didn't have the space, and the mare was old so she was just giving her away. I had a bit of space and some free time, so I said, sure, why not, thinking that she would be a companion for my own riding horse.
The mare arrived, turned out to be an unbroken 16 year old broodmare. A year later she was competing in riding club. She was such a success story that when I was offered another one from someone else I said yes.
The problem with that is that it very quickly snowballed.
People who have older horses, or unridable horses, or just ones that they can't afford to keep anymore, or ones with issues or foals they can't handle, they generally know someone who knows someone who knows me. And as most owners would rather give the horse away then have it put down, I get a phone call.
We've recently had to move because I need more space. I don't really ride much these days, instead I just look at my horses over the fence.
I trained as a veterinary nurse, and I have a friend who's a vet who treats my horses for free, another friend is an equine dentist and she does my horses teeth in return for me breaking her horses. I took courses in college on farrierry, and all my horses are barefoot, so I do them myself too. All of which keeps the cost down.
The main cost is feeding. We are making our own haylage this year, for the first, so that should keep our costs down more.
I'm by no means the worst person for hoarding, I know a guy who hoards horses too, he's well over the 150 mark, but doesn't know exactly how many he has.
Also, in terms of behaviour of the person, I'm totally normal and well adjusted with no psychological issues, and I have the paper to prove it. I'm also really soft and very emotional and am a sucker for a sad case.
That seems to be the mind set of the other people I know in the same situation. They all think they are doing something good. And a lot of the people are. But it's hard to keep it under control. I have to be realistic about what I can do on my own, or even with help. And that's why every year I have to have a sort of cull - passing on the horses that don't need me to someone else, rehoming them or loaning them out to someone else.
I'm very careful about welfare and care, and I ensure, much to my bank managers disaproval, that my animals are well fed and well cared for.
But my main issue is space. I just don't have enough stabling, and so most of them live out ok, but I have to keep space for anyone who is is sick or about to foal.
It's time consuming, and I have very little help.
Other people I know and know off, who have been in the same situation have suffered because they take on more than they can cope it, and so the sick animals get sicker, and the old get thin and weak, sometimes without anyone really noticing.
There are lots of articles on google about animal hoarding. And the RSPCA have some very good resources about it, so I suggest giving them a call.