When their bladder is full.
A healthy horse should urinate about once a day, maybe twice if they have drunk a lot. e.g. on a hot day your horse will naturally drink more to cool itself down and obviously to quench itself, so to allow the water to be stored in the bladder, it must be emptied by urinating.
I can tell by your question that you haven't spent much time near the tail of a horse. It really depends on what you have been feeding your horse. Rich, green grass in the spring will turn your 1 horse-powered friend into a jet propelled gas machine. Especially when running, a too-rich diet can result in flatulence every few minutes.
They normally leave about two to three piles of dung, but that can very depending on the amount of hay and grain you give them.
1-3 depending on how much they have to drink.
as often as you feel the need too...it depends on how much fluid you intake daily. The average adult bladder holds approximately 1 pint of liquid so you should urinate as many times as your bladder is filled daily. This means, if you drink 2 pints of liquid you should urinate at least twice before you could drink anything else, unless of course you wanted to urinate on yourself.
DailyDaily
Daily you should always clean your horses stall at least once a day
A horses stall should be cleaned every day if possible but if not every other day.
I own horses and they get their sheaths cleaned every six months.
You should take in atleast 2000-2500 ml of water a day to maintain healthy fluid balance in the body. You normally urinate about 1500 ml of that.
a stall?? Once daily...
you should really clean your horses stall from 3-6 days of the week.
A horses stall should be cleaned every day.
The kits (babies) still urinate but they are small animals and don't go often. My Flemish Giant didn't urinate a lot when he was a kit but since he's grown he goes more often.
The liver is breaking it down so quickly that its trying to get it out of your body causing you to have to urinate often.