Horse drinks a lot of water but no excessive urination.

My mare is a 19y/o National Show Horse and 320 days pregnant currently, however, prior to being bred we noticed this phenomenon. She drinks a lot of water. In less than 12hrs she will down 10gal if not more but there’s no excessive urination/wet spots in her stall. She isn’t bloated nor gaining any amount of water weight. Where is it all going? She’s not noticeably sweaty, but could she be sweating it off? When in regular work in the past she has always been quick to sweat and in copious amounts. However, she’s not been in regular work since December 2014 when she strained a suspensory ligament. Her coat isn’t long though she did start shedding sooner than the rest of the herd. Her BCS dropped to a 4 at the breeding farm last summer and it was extremely difficult to get weight back on her. It took us nearly a full year to get her back to a BCS of around a high 5, low-ish 6 and that was with trying everything under the moon and forking calories at her as safely as possible. Now she’s starting to go off her feed but still persists with drinking large amounts of water (at least 2x as much as the other horses in comparison, even when compared to the other pregnant mare). What could be going on?

10 gallons in 12 hours during hot weather is normal for many horses.

Carrying a foal also increases blood volume significantly, so perhaps she has greater fluid requirements to match.

If you’re concerned, it might be worthwhile to pull some bloodwork?

10 gallons in 12 hours during hot weather is normal for many horses.[/QUOTE]

This. If you are estimating 10 gallons because she’s drinking out of 5gal buckets? They really don’t hold a full 5gal unless at the absolute brim. Most barns I’ve been in fill 5 gal buckets at least 4 times a day in summer around here plus they drink an unknown amount on turn out, even if all they are doing is standing around. No difference in pee quantity from cooler weather when they consume less so guess they are losing it through sweat even if it doesn’t look like it to a casual observer.

Doesn’t sound like much of an issue and you say it’s normal for her but, as always, your vet is the best one to ask.