....."I would think less water equells less pee,maybe not. ".....
The above does not apply in certain disease states, such as IR or PPID. The increased urine production is what is driving the thirst, not the other way around. There is above-normal urine production bc the horse's urine is being diluted by the disease process (whether its increased glucose spilling into the urine, or other dilutant). The kidneys then force more of the body's water stores than it normally should into the urine -- simple osmosis at play here. Because the horse's urine is so diluted, its body must tell itself to drink more to keep up the necessary water stores. By denying water access, the horse will become dehydrated rather quickly because the horse is still is a diseased state and diluting the urine abnormally.
You may seem the shorthand term "PU/PD" occ tossed around -- thats polyuria (increased urination) and polydipsia (increased water consumption). These two states often go hand-in-hand but its the excessive peeing thats causing the excessive drinking, and thats why you cannot safely limit the water access. Correcting the underlying cause of the PU/PD is the only safe way to curb the excessive urinations.
You'll find this hard to believe at present, but being able to know exactly how much your IR/PPID horse is drinking and peeing is actually a good indicator of day to day disease status -- often PU/PD is one of the first signs that glucose and/or insulin is climbing.
Hopefully we'll get some much-needed answers on the 27th!
Hang in there,
Kerry in NY