sometimes i need to coax our guy to drink more in the winter by using beet pulp, a lot of horses colic (impaction) from lack of water in the late fall/winter~ so yes he does drink more in the summer.
as far as your second question, im not sure if its 20 hours??
Our horses drink better in summer weather, when they are warm or eating hay. Dry hay does make them drink more.
For winter, we heat the water in tanks, give them extra salt in their grain. Most get one tablespoon of white feed salt, once a day. A couple poor drinkers get two tablespoons a day. Seems to help them drink a bit more daily. One poor drinker has a heated bucket, along with a plain water bucket in her stall. The plain one doesn't freeze until it gets below 20F.
Wet beet pulp has warm water on just before feeding. They like that in cold weather, readily eat it up.
I do not think horses need to be eating hay 20 hours a day. Mine would be blimps! They eat hay, which then ferments in the gut, causing heat to keep them warm outside. They get extra hay if the outside temps get down into the teens or below, so they keep warm. Not much, but some hay. We do not give extra grain or beet pulp on cold days. We do feed a lot of hay in winter, with them getting 1/2 to 3/4 bale total each, every day. We feed pretty good hay, so lots of nutrition, without going to huge quantities for their large sizes. They are outside EVERY day it is not icy or sleeting, have fields to go out into.
The digestive system of the horse is designed to "forage" ie. walk around for miles and miles searching and nibbling at food all day (like they do in the wild). We don't mimic that at all in our feeding practices, more for our convenience than anything else. And they are fed much richer and nutritious food than they get in the wild, which is why if they ate for 20 hours they would become blimps.
Not too many people feed very small amounts of hay and concentrates many times per day-nobody has that kind of time! Instead many of our horses are kept inside for part or all of the day, turned out in a tiny area relative to the hundreds or thousands of acres they would have in their wild habitat. This means they park at a round bale or pile of hay for the day-especially in winter. High energy concentrates once, twice or maybe three times a day for the average horse-many times for racing TB's and SB's.
Many horses seem to adapt and do OK-but the difference in what the digestive system is meant to do vs. what it is forced to do contributes a great deal to ulcers and colic, and other digestive related problems like choke and dental problems.
Can you tell I love my Biology! One of my favourite lessons to teach in my class is the digestive system and how we contribute to all sorts of problems with our management practices. Gets them thinking!
My two will go through a muck bucket (20 gallons?) every 24 hrs. and they are turned out 24/7. Their water consumption does dip in the winter. At first I thought this was due to the heated bucket I was using (had fiancee hook up a voltmeter just to check!) shocking them. After eliminating that, I just chocked it up to seasons changing. I add electrolytes or salt, depending on what I have on hand and they get sloppy beet pulp mashes twice a day. Plus they both love to eat snow .
As for hay, I use outside hay feeders and Nibblenets inside (they have free access to their stalls) and have found that even when I put out hay for 12 hrs. at a time and then head to work, they still have some left when I get home. I have noticed they will nap and hang out for a few hours, then eat for a few hours. They have food accessible, but only seem to eat when they need to. Neither one is a blimp, but never go hungry either.
yes, horses are designed to graze ... eat a little bit alot of the time. Up to 20 hrs. a day BUT ... that's clipping little blades of grass with their teeth as they can find them, picking out the tasty weeds and herbs, nibbling on leaves of trees and bark of trees etc. ... LITTLE bits at a time; not piles and piles of 'stuff' doled out once or twice a day.
I do feed free choice hay and my guys will eat for awhile then rest then play then eat again - they don't stand and eat constantly for the entire day or night. They have their routines. But when they're wanting to 'graze' (I have little to no grass right now) then they have their hay. I do spread it out for them so they have to walk around to mock-graze the little piles scattered around. This way, too, it doesn't matter WHEN I get them their 'grain' (hay replacer cubes, fresh fruits/veggies/nuts/seeds mixed with some cracked corn during winter for extra calories and heat) --- cause they always have something to nibble on and don't ever get that frantic starving attitude.
As for drinking - yes, when its rainy, windy, cold - they drink less. We do warm up the tubs at night with buckets full of scalding hot water to melt the ice and warm the water to tepid/warm temps. They all wait for this and will stand and drink alot at that time. They LOVE their warm water!
To encourage them to drink during the cold/rain/sleet/windy winter days I will add a tbsp. of Himalayan or Celtic Sea Salt to their 'grain' or veggies/fruits etc. that I feed just once a day. The Him and Celtic salt will add minerals and other nutrients they need as well instead of just plain, processed salt. I also have a Himalayan lick for them available free choice.
Once a week, also, I'll make up a warm mash for them with plenty of warm water and goodies.
So far, so good knock on wood. All stay hydrated well and seem comfy most days.
Will a horse drink more water though to cool off? You know, like when you're hot and sweaty, you'll drink some water to cool back down. Do horses do the same thing? Would wearing a sheet make a difference to the amount of water consumed overnight? Just curious.