Water
Water is certainly the most overlooked ingredient in the horses diet but is, as you might predict, absolutely, the most essential.
The body is made up of 65-75% water and this water plays a vital role in transporting blood cells and nutrients around the body. The water in the body is also important for thermoregulation whereby during exercise, sweat is produced, which then evaporates from the skin’s surface helping to keep the horse cool.
How much water does a horse need?
The amount of water required by the horse is determined by the amount of water lost from the body.
These losses occur through faeces, urine, respiratory gases, sweat and, in the case of lactating mares, milk.
The losses are affected by the amount, type, and quality of the feed consumed. Interestingly horses consuming all-hay diets drink more water than horses fed a large amount of concentrate, coupled with hay or a complete pelleted diet. Also other factors to consider are environmental conditions, such as temperature, health, physiological state, and the physical activity level of the horse.
Exercise levels and climate also have a large impact on the losses sustained. Horses at rest in a moderate climate will generally consume around 15-22 litres (based on the average 500kg horse). Horses grazing lush spring grass could therefore potentially meet their maintenance requirements from grass alone. However in general this is not going to be possible and so fresh clean water should always be available.
On the other hand, water intake can increase to over 90 litres per day for exercised horses. Heat and humidity also increase water requirements, especially in exercising horses. In one trial, conducted by Kentucky Equine Research, daily water intake increased 79% when horses transitioned from a thermoneutral environment (20°C and 45-50% relative humidity) to a hot, humid one (33-35°C and 80-85% relative humidity).
Life stage must also be noted as for example lactating mares may drink up to 75 litres per day due to the fluid losses associated with milk secretion and the increased consumption of feed to support milk production.
The effects of dehydration
Dehydration can occur when the horse loses excessive amounts of fluids through sweating, drooling, respiration, normal excretion (urinating and defecating), and even diarrhoea, if fluid replacement isn’t adequate.
For example after a cross country phase, horses can lose 15-20 litres of sweat and an endurance horse could lose double this during a race!
It can be difficult to monitor how much your horse is sweating and the skin-pinch test is inaccurate. However, a good way of estimating fluid losses is to use a weigh-tape. It is generally accepted that 90% of a horse’s weight loss after exercise is due to sweating and 1kg of bodyweight equates to approximately 1 litre of fluids. This allows for a relatively easy estimation of the number of litres lost.
To complicate the issue of calculating dehydration levels, it is worth noting that the horse has a large hindgut which can hold around 30-40 litres of fluid. This fluid can be drawn upon in situations of fluid loss, and so the exact amount of fluid loss that would result in issues for the horse is hard to pinpoint.
However its seems that for fit well adapted horses, 3-5% of body mass loss due to fluid loss causes little issue. This equates to around 15-25kg of weight loss in a 500kg horse. Yet, whilst it may not be an emergency in this case, fluid and electrolyte losses even below this level must be replaced over time to avoid dehydration. This is even more vital for those exercising strenuously over several days.
Some practical indicators of dehydration that you can look out for include (but are not limited to):
- Fatigue
- Muscle spasms or sign of pain
- High body temperature
- Dark urineor no urine passed for extended periods of time
- The appearance of the mucous membranes— if they are congested and are red in appearance, the horse is likely to be dehydrated
How to rehydrate
Simply drinking water after exercise will not be enough to re-hydrate a dehydrated horse properly as the body cannot hold onto water without the presence of electrolytes. If electrolytes are not provided along with water, the water simply dilutes the body fluids surrounding the tissues, which in turn “turns off” the thirst mechanism.
The best rehydration therapies therefore include the use of electrolyte preparations, either in feed or water, to stimulate drinking. However, whilst electrolytes can be given in water, the volume that a horse will readily consume will not allow for a large intake and so electrolytes given in this way are unlikely to adequately replace losses. It is therefore advised that electrolytes should be given in the feed or as a paste as this is leads to a higher consumption level. However if this is not possible, then providing them in water should still be done.
For horses at rest that are not losing large amounts of sweat, or fluids through illness such as diarrhoea, it is generally not necessary to provide an electrolyte supplement as their water losses will not be as great. A diet consisting of quality grazing and additional concentrates along with plenty of water would be enough to ensure a good level of hydration. If the horse is not receiving any concentrates a balancer could be considered to ensure the presence of adequate daily essentials.
However, for those losing larger amounts of fluid, such as a horse worked on a regular basis, or one exposed to extremes of heat, that therefore sweats visibly (particularly forming white foam), an electrolyte supplement is likely to be necessary as the diet is unable to supply the larger amounts that are needed. However, it is still important to note that even in these cases, the majority of the electrolytes should be coming from a balanced diet over time.
