Should a horse stall be cleaned daily?

At a very minimum, a horse's stall should be cleaned daily. Preferably, a stall should be cleaned twice a day.
Leaving urine and feces in a stall for an extended period of time can lead to many health problems for your horse. Thrush, a fungi, can develop in your horses feet due to the bacteria and moisture left by urine and feces. This can lead to lameness and extreme cases severe permanent hoof problems. Respiratory issues are also caused by the ammonia in urine. Skin problems, such as scratches and other bacterial infections, can develop on the lower leg of a horse.
Overall, cleaning a horse's stall will make him happier and healthier, imagine standing in your own urine and feces all day--not fun!