Hmm, not sure about unlimited. Howrse is the only game I know who does that... it's insane, some users have 200,000+ horses. In total, nearly 14 million. o__o Their database must be terrifying. No idea how they keep everything running so fast.
It must be expensive too! I just assume they started off with unlimited horses and didn't expect it to be a problem, in the early days of a small game. Then they didn't dare to upset players by forcing a limit later? Dunno, it seems a baffling decision.
Then again... they might be making money from it. People will still buy zillions of the newest Golden Apple horses, top skillers and other expensive collect-y things, knowing they don't have to make space first. Just £1 spent on a horse would more-than-cover the hosting of that single row of data in the DB.
... dunno, we'll see. I'm just a single idiot with a few pennies to spare, not a game company who knows how to optimise a database and let it scale-up infinitely. Perhaps I'll learn that stuff later xD Or maybe a high limit of 5000 or sth would be enough to satisfy you? ... Does anyone on here even have 2000+ beasts? o.O
(now I'm reminiscing about OotG again. 20 flock spaces... ahh those were the days! Everyone fretting and squabbling over which of their beautiful griffs to throw out, to make room for an even more beautiful one...)
/ goes to explore Tundra