A few years ago I read an article
describing research done at New Bolton Center on drinking behavior. It
said that the research showed that in winter, horses prefer to drink
warm water rather than ice cold water, and as a result veterinarians
recommend giving horses warm water during the winter to be sure that
they drink enough.
So, that winter we hung buckets of
water along the fence every morning and evening at feeding time. It
seemed our horses drank very little warm water from the buckets.
Instead, they kept going to the stream even when it was partially frozen
over. On days that the stream was completely frozen, they would drink
from the buckets. We thought they might not like something about the
hanging buckets, which were quite a distance from their hay racks.
So, the next year we put a heated
plastic stock tank in the pasture near the hay racks. We put in a large
heating element so the water stayed warm to the touch. Again, once we
started heating the water in the tank, our horses seemed to drink mostly
from the stream, as if they really preferred the ice cold stream water
to the warmed water in the tank.
This year, the day before
Thanksgiving, we had a sudden cold snap. I filled up the stock tank, but
forgot to plug in the heating element. In the morning, there was a thin
layer of ice on the tank. We were surprised to see that the horses had
been drinking from the cold tank, breaking through the icy crust.
Anyway, I turned the heater on so it wouldn't freeze. After two weeks of
paying close attention, I'm pretty sure they don't seem to drink much at
all from the tank when the heater is on. They are going back to the icy
My veterinarian and I were talking
about this, and she thought you might have been involved with drinking
behavior research cited in the magazine article, or that she might have
heard you talk about it somewhere. Was that you, or do you know about
it? Do you have an explanation why in these circumstances our horses
drink the ice cold water from the creek or tank rather than the warm
water in the buckets or the water that is warmed in the tank? It would
seem they actually prefer cold water over warm water.
Robert, New York
Thank you so much for bringing up this
question. I was involved in the research on effects of water temperature
on drinking behavior. You are right that there has been some confusion
about the results, and it is great to have the opportunity to clarify
what we know.
The observations you describe and your
tentative conclusions that your horses prefer icy cold water to warm
water are exactly consistent with the findings of that study. What we
found was that if during cold weather horses have only warm water
available, they will drink a greater volume per day than if they have
only icy cold water available. But if they have a choice between warm
and icy water simultaneously, they drink almost exclusively from the
icy, and drink less volume than if they have only warm water available.
So in the experiment, we had "single option" comparisons,
where each subject had only one bucket, either cold or warm. After a
period of time on that system, each subject would be switched over to
the opposite temperature, and after a period of acclimation, drinking
behavior and volume of water consumed was compared. We also did separate
"preference" experiments, in which each subject had two
buckets available simultaneously, one icy cold and the other warm.
Unfortunately, if the full scientific
report is not read carefully, it's easy to conclude that "horses
prefer warm water," rather than the more complex findings we
reported. I remember several articles and news clips in horse magazines
that described the quick, but incorrect conclusion. Over the years I
have had many calls with questions such as yours.
My co-investigator for this project was
Michaela Kristula, DVM, Section Chief of the Field Service group at New
Bolton Center. She had the clinical impression that horses and ponies
tend to experience a higher rate of impaction colic during the first
deep cold spell of the winter. She, like many others before and since,
had wondered whether horses might not drink as much water when it turns
icy, which could increase the risk of impaction colic. She wondered if
horses avoid icy cold water, especially during the first cold snap of
We have thought a lot about how to
explain these findings, but have no good scientific evidence for an
explanation. In human terms, we have wondered whether the basic instinct
of the horse is to drink the coolest water available. This behavior
might be adaptive in the sense that in nature the cool, running water
probably is the freshest and least likely to be contaminated.
Then we would have to explain why they
would drink a greater volume if the warm water is all they have. We have
wondered if warm water is less satisfying to thirst. Or maybe icy water
is less comfortable to ingest in large quantities, or that the icy
crusts might deter long drinks. These are really only guesses, and we
would have to do much more than the couple of small studies we did to
address them properly.
Since that study, Dr. Kristula has
recommended that if you want to increase the volume of water your horse
drinks in winter, provide warm water and make sure there is not a source
of cold water. Even though a horse might choose cold water over warm, it
will most likely drink a greater volume if the only water available is
In those studies, we observed some other
interesting aspects of drinking behavior of horses. For example, horses
in stalls which are fed hay and grain typically do most of their
drinking within a few minutes after eating their grain and within an
hour or so after they are given hay. That observation has been fairly
consistent in other drinking behavior and nutrition studies of horses.
We also saw a lot of hay wetting behavior, in which a horse dips each
mouthful of hay or places a flake of hay in its water before eating it.
You can read the original research
journal reports of the winter study and a follow-up study done in the
summer. The journals can be found in most university libraries, and
copies of the papers can be viewed and downloaded from our laboratory
web site (www2.vet.upenn.edu/labs/equinebehavior, click on Reference
Library and the Lab Publications).
The citations are:
Kristula, M.A.; McDonnell, S.M. Drinking
water temperature affects con-sumption of water during cold weather in
ponies. Applied Animal Behaviour Science 41: 155-160, 1994.
McDonnell, S.M.; Kristula, M.A. No
effect of drinking water temperature on consumption of water during hot
summer weather in ponies. Applied Animal Behaviour Science 49: