The importance of water in winter — why your horse could be more dehydrated now than in the summer *H&H Plus*

Whether he’s indoors or out this winter, a horse’s health can soon suffer if his water intake drops – as Rebecca Hamilton-Fletcher MRCVS explains

Often referred to as ‘the forgotten nutrient’, water is essential for all life. Without it, dehydration occurs and most physiological functions, including digestion and growth, rapidly become compromised.

Most people are conscious of the need to drink plenty during the summer months, as our own increased thirst is directly related to the hot, sticky conditions. In contrast, during the winter months we naturally drink less. It is easy to assume that our horse’s needs will be similar.

Whereas most horses are out in summer eating grass, however, with its high water content, during the winter many are stabled. Their grass intake is supplemented or even fully replaced by a forage hay diet, which has a relatively high dry matter content. Drinking enough water to compensate for this unnaturally dry diet becomes vital.

Various factors will affect a horse’s water requirements during winter.

Points to consider include the horse’s management. Is he at grass, or predominantly stabled and on a dry forage diet? What is his workload — is he hunting twice a week, or only hacking out occasionally?

Temperature will play its part. A clipped-out horse is less likely to lose fluids through sweat while working than one who is fully coated. Being over-rugged, especially given that our winters are getting warmer, will increase thirst.

A horse’s age can significantly increase his water requirements. Equine veterans may already have compromised digestive capabilities, while those suffering concurrent clinical conditions such as pituitary pars intermedia dysfunction (PPID), or Cushing’s, may be influenced by an excessive endocrine-driven thirst.

Given adequate water, under natural conditions most equines appear to self-regulate their winter water needs. This balance is only really upset when we interfere, by feeding an overly dry diet, perhaps, or by clipping and over-rugging.

Dehydration can occur relatively quickly during the summer months and is usually related to a sudden increase in water loss, such as excessive sweating. In winter, dehydration is often insidious and is more likely to be caused by inadequate water intake.

An affected horse may be depressed, lethargic and easily fatigued, with a dull coat, sunken eyeballs and a tucked-up appearance. His droppings may be infrequent, small and hard in texture, and his urinary output may decrease and become darker in colour.

Additional signs include dry mucous membranes, reduced salivation and a loss of appetite. The horse may become uncomfortable, with visible muscle tremors, a subnormal temperature and an increased heart rate. The skin on his neck may not return to normal following a pinch test, although this is not considered a reliable indicator.

Impaction danger

By far the most common winter veterinary issue is impaction colic, or constipation.

Representing approximately 10% of all colics, impactions occur when water is reabsorbed in the large intestine from an already relatively dry ingesta (food intake). This slows the passage of the food, allowing even more time for further water to be reabsorbed. Gradually, things grind to a halt, with the blockage usually building up at the narrow U-bend of the hindgut known as the pelvic flexure.

Symptoms can be subtle at first and are often missed. If the issue is caught early enough, stomach-tubing fluids, electrolytes and possibly liquid paraffin may be sufficient. Often, however, by the time the vet is called the blockage is pushing right back into the pelvis. It can then take several days of intravenous fluids and medical analgesia until everything is moving again.

While other factors can contribute towards impactions, including poor hay quality, inadequate trickle feeding, a lack of exercise, intestinal parasitism and compromised dentistry, the most significant is insufficient water intake. These colics often begin after a sudden, sharp cold spell, when feed, exercise and water may suddenly become compromised and the horse is unable to adapt quickly enough.

The equine urinary tract appears to be surprisingly resilient to dehydration, and incidences of renal or bladder stones are uncommon. Other factors, such as excessive dietary calcium (leading to a calcium carbonate-rich alkaline urine), are usually involved. Attention should always be paid to urinary output, however. Any signs of dark, concentrated urine, perhaps with blood, and accompanied by low-grade abdominal pain, warrant veterinary investigation.

Beating the freeze

So how can we ensure adequate water intake in winter?

Freezing over of water is one of the biggest challenges. Ice must be regularly broken and removed in its entirety, and containers will need topping up much more frequently. Electrically heated automatic drinkers and buckets are available, but they are expensive and the electrics must be impeccably maintained. A horse’s sensitive muzzle will easily sense any stray voltage in the water, which will put him off drinking very quickly.

Research by the University of Pennsylvania, USA, found that horses drank up to 40% more if the water was warm, and less if offered chilly water. When presented with both options, however, horses would choose the chilly water. It thus follows that horses will drink more during cold weather if the water is heated, but only if no other source of water is available.

They also found that stabled horses do most of their drinking within a few minutes of eating their hard feed, and within an hour or two of consuming their hay. They should therefore always have access to at least two buckets of water at feed-time – preferably warm water, if prone to impactions, or if there has been a recent drop in ambient temperature.

Additional ways to increase water intake include feeding soaked hay or haylage instead of dry forage, making hard feeds sloppy by adding water and increasing the amount of time spent at grass. Ensure that all horses turned out have plenty of safe access to shared water containers, so that even the most submissive are not discouraged from drinking.

If your horse is working hard or has additional needs, ask your vet about adding salt and/or electrolytes to his feed. These can also be added to his water, although plain water must also be made available in case he dislikes the taste.

Since several diseases use water as a vector for infection transmission, biosecurity is especially relevant where horses are sharing buckets or troughs.

Just one drop of infected nasal discharge contains sufficient Strep equi bacteria to infect 2,000 horses with strangles. In winter, this source of infection can last for several days on inanimate objects, such as buckets, and up to a month in water. The EHV-1 equine herpes virus can remain stable and infectious in water for up to three weeks, while the equine flu virus is only slightly less durable.

Containers must be regularly cleaned or disinfected, especially if shared, and filled with clean, fresh water. Horses can be selective and will be reluctant to drink if the water provided is dirty, unpalatable or foul-smelling.

Crunching the numbers

85% – moisture content of summer grass; dry hay contains just 10%

4 litres – the water required to digest every kg of dry matter ingested

40 litres – the water a 500kg horse, eating 10kg of dry matter daily, needs for digestion alone

10 litres – average water bucket capacity

5 minutes – the time an average horse spends drinking per day

Winter watering methods

Buckets

PROS: allow intake to be monitored

CONS: capacity is limited; can be kicked over or broken; labour intensive; freeze easily

Trough

PROS: good capacity

CONS: individual intake cannot be measured; difficult to keep clean; can freeze over; infection transmission risk if shared

Automatic drinker:

PROS: a constant supply; rarely freezes if pipes are lagged

CONS: cannot assess intake; risk of unnoticed mechanical failure

Ref: Horse & Hound; 10 December 2020

Watch the Horse & Hound Awards 2020 virtual ceremony