It’s easy to think that dehydration only affects horses in the warmer summer months when they are hot and sweating a lot. However, frozen drinking water and dropping temperatures in the winter months can result in some horses actually drinking less, increasing the possibility of dehydration.
Keeping horses hydrated in winter can be a challenge, largely due to the climate and food sources available. Water intake is intrinsically linked with appetite, and a horse which has a reduced appetite for any reason, or reduced food intake due to scarce food supply, will inherently drink less water.
Horses tend to receive more hay or haylage than grass in winter compared to the summer months, which is a much drier diet. Grass is around 80% water in composition, and this water must be replaced by an increase in drinking by the horse if they are to remain normally hydrated on winter rations. Horses should have forage (hay/haylage or grass) available constantly, unless there is a medical need for restricted rations.