Salt requirements for endurance horses

by Dr Rensia de Wet, manager of Zabeel Feedmill, Dubai, UAE

Common salt is composed of ­approximately 60% ­sodium and 40% chloride. Both ­sodium and chloride are ­needed in the diet for regulation of all body fluids, maintenance of the acid-base balance, and generation of the ­membrane ­potential and conduction of ­electrical ­impulses in nerves that allow ­muscles to contract and flex.

How do horses acquire salt?
Many feeds, including natural feedstuffs such as pasture grasses, contain less than 0,1% sodium and thus less than that ­needed even for unexercised horses. In addition, ­increased salt intake in the ­additional feed consumed as a result of ­exercise, is not ­sufficient to ­compensate for increased ­sodium losses that may occur with ­exercise.

Exercise increases salt requirements proportional to the amount that it ­increases sweating, as sweat contains a significant amount of both sodium and chloride. Therefore, sodium chloride is often added to concentrates at a rate of 0,5-1%, and salt should be available at all times for ­free-choice consumption by horses.

The most popular way to feed salt ad ­libitum is a salt block. These were originally designed for cattle (which possess a rough tongue), but are suitable for most horses. Occasionally a horse may be seen biting or gnawing at the corners of the block. This behaviour may indicate that the horse is not receiving enough salt through typical licking. In these instances, the preferable way to feed salt is loose.

Although there are formulations on the market designed especially for horses, plain white table salt is acceptable. Loose salt can be offered in a hanging bucket in the stable or run-in shed. For horses that do not have access to a stable or run-in shed, the loose salt should be placed in a covered feeder in the pasture.

Pecking order becomes a factor in herd situations. If many horses are kept in a ­pasture together, timid horses may be kept away from the salt by more ­aggressive ­horses. Placing salt in two distant locations will ensure that all horses have access to the mineral. Consumption of loose salt is ­generally greater than block salt, but salt intake is more consistent from week to week when offered a block.

Requirements
In feeding horses, if salt is available, horses will consume enough to meet their needs. Sodium is the only mineral for which a ­clearly defined appetite exists and ­therefore, if available, will be consumed by animals in an amount sufficient to meet their needs. There is, however, a wide variation in the amount of salt consumed by horses ­under similar conditions, from 9-143 g/day ­between ­horses, and from five to over 200g by the same horse on different days.

Some stabled horses allowed free ­access to salt may, because of boredom, consume excessive amounts of salt, resulting in ­excess water consumption, urination and a wet stable. If this occurs, add 30 g or two tablespoons of salt daily to the grain fed, and do not allow free access to salt.

The National Research Council suggests that horses at rest need approximately 25g of sodium chloride per day. Heavy workload ­increases the sodium requirement ­substantially with equine athletes requiring up to 200 g.

An endurance horse may lose 25 ­litres of sweat during a 100-mile ­competition. This amount of sweat would contain ­approximately 93 g of sodium and 163g of chloride. When electrolytes are lost in sweat and not replaced throughout an exercise bout with a suitable electrolyte ­preparation, horses may exhibit fatigue and muscle weakness.