Salt and fluid balance

What salt does in the body

All mammals need salt to maintain normal cellular functions. This applies both to fluid balance and to communication between the nervous system and the muscles. Without salt, neither fluid balance, muscles nor nerves work optimally.

Not getting enough salt can have serious consequences for horses and humans alike. That is why it is not a supplement you choose to add or leave out as needed: it is a daily essential, on a par with water and forage.

What the published science says

INRA is the European recommendation for equine nutrition, based at Wageningen University in the Netherlands. NRC 2007 is the official US recommendation for the minimum nutrient requirements of horses. Both show that 10 grams of salt per 100 kg of bodyweight per day only just covers the requirement.

In addition, a range of Swedish research over a period of 25-30 years states that the requirement is 2 grams of sodium (Na) and 8 grams of chloride (Cl) per 100 kg of bodyweight. For a 500 kg horse, that equals 10 grams of sodium and 40 grams of chloride a day respectively. So there is agreement on the level in Europe, the US and Sweden.

There is scientific agreement that horses need at least 10 grams of salt per 100 kg for maintenance, and more in hot weather, during work and in pregnancy and lactation. Our recommendation is 10 g per 100 kg on top of Every Day Happy or Peak Performance, which themselves provide approx. 3 g, and 13 g in total, e.g. with Supreme Minerals. This is in line with the sources.

How much salt your horse needs

The base figure is 10 g per 100 kg of bodyweight per day for maintenance and light work. This applies on top of Every Day Happy or Peak Performance; with Supreme Minerals, give the full requirement of 13 g per 100 kg for maintenance and light work. For moderate work, give 15-17 g of salt and for demanding work 22-27 g per 100 kg on top of Every Day Happy or Peak Performance (with Supreme Minerals, 18-20 g and 25-30 g in total). Hot weather and lactation also increase the requirement.

The figures are dry weight. Multiply the base figure by your horse's weight in hundreds of kilos, and always feed according to your horse's current weight, not its ideal weight.

Salt deficiency: what happens in the body

A long-term lack of salt throws the horse's fluid balance out. The horse finds it much harder to regulate muscle work, energy and inflammation, and copes less well with sore hooves, muscles, joints and tendons.

A lack of salt can be the direct cause of colic, because the horse drinks too little. It has a negative effect on all muscle function, including gut peristalsis, which is smooth muscle. Your horse needs salt in sufficient amounts to have good working energy and stamina, to work correctly through the body and to build or maintain a good topline.

Why deficiency has become common

In the past, hay was salted and there was more salt in compound feeds, which horses were given in much larger amounts, often 3-4 kg of grain a day. Horses are hardly fed like that any more. Salt deficiency is probably a significant contributing factor in many horses' health problems, from colic to musculoskeletal injuries: when the muscles become overtired, other tissues such as tendons and ligaments are overloaded.

Signs you can act on

• Your horse drinks too little, which in itself can trigger colic
• Sore hooves, muscles, joints or tendons
• Lack of working energy and stamina
• Difficulty building and keeping a good topline
• Your horse goes at the salt lick greedily, which is typically a sign of a deficit

What makes the requirement rise

The salt requirement increases during work where the horse sweats, in hot weather and during pregnancy. During lactation in particular, the requirement is almost double that of maintenance and early pregnancy.

When your horse seems to eat too much salt

When some horses appear to overeat salt, they are probably in deficit, unbalanced in their nutrition and therefore exhausted or unbalanced in their adrenal function. The same pattern is seen in other species. In studies where salt was removed for a period to investigate the physiological consequences, markedly larger amounts than the maintenance level were given afterwards to correct the deficit quickly.

The consequence of a high salt intake is that the horse, like humans, becomes more thirsty, and the fluid eventually has to leave through the kidneys as urine. So the horse drinks more and urinates more, which may cost extra bedding. It is not dangerous for the horse to take in extra fluid if it has normal kidney, heart and circulatory function. If you want a real sense of fluid intake, you can let your horse drink from a bucket or tub.

If you suspect your horse is overeating from the salt lick, it is a good idea to give loose salt in the correct amount directly in the feed, adjusted to your horse's size and workload. Weigh the salt lick once a month so you know how much is being eaten. As a rule there is no problem once you do the maths.

How to give salt in practice

A salt lick alone is not enough, because most horses lick it too little. So give the salt in the manger, so you know your horse gets what it needs.

• Start with ½ tsp of loose salt in the manger, and build up over 14 days
• Use a fixed measuring spoon so the amount is the same every day
• Weigh the salt lick once a month if you want to know your horse's own intake
• On summer grazing: give loose salt in a manger under a shelter, and note down how much you put in, e.g. every other week or monthly. Then you can work out how much disappears relative to the number of horses in the herd

Salt is easy to mix into a mash together with Every Day Happy, Peak Performance or Supreme Minerals. Fibre mash soaked in water with a vitamin and mineral mix plus salt acts as a storage depot that travels through the horse's gut. The transfer of nutrients from gut to bloodstream is optimised, because the horse gets the chance to absorb them at the pace it needs.

If you want to check the requirement yourself, you can see your horse's needs in a feeding program such as SundHest.dk or look it up in Den Store Foderbog. Then find a suitable measuring spoon and give your horse the salt it needs in its feed.

Related articles on salt and fluid balance

• Electrolytes for horses: why salt is often the most important
• Winter laminitis, circulation and salt
• Horses need salt

This page is based on the article on horses and salt that Regulator Complete wrote for Malgré Tout, compared with INRA, NRC 2007, Swedish research and Den Store Foderbog.