Generally, this term is used by those who need to release urine. The symbolism of "long horse" and "shortwalk" are up to the user's interpretation.
John: You know, though our conversation is enthralling, I admit I must taking the long horse for a short walk. In other words, I must urinate, as you may know from the saying's entry on Urban Dictionary.
Jane: Ok.
Derived from the latin word sha, which means explosive diarrhea. The term differs from the phrase taking a shit because of the shear explosiveness of the action. The term is often used to get out of work for a week or more.
Man, I have been taking a shaw all freakin day. You can count on me not coming to work for at least the next 3 weeks. If you need me I will be watching Dexter.