Adding salt to feed is becoming a hot topic out there in horseworld, and for very good reasons; apart from seeing significant positive benefits in your horse, it's an absolute 100% essential nutrient.
So what's this salt-thing all about? Well, it's that old mineral-balancing minefield again. And this time the culprit here is potassium, or rather, the potassium:sodium imbalance.
Firstly, a bit about salt, and in a nutshell it provides a basic, essential electrolyte to our horses. Electrolytes are minerals dissolved in the blood stream which have the capacity to conduct electricity. They play a key role in normal nerve and muscle function, and they also help the body keep body fluids in a normal balance.
Factors contributing to the electrolyte imbalance include species and stage of growth of the grass, grass management, weather, feeds and supplements, all of which have a cumulative effect on electrolyte balances.
Potassium in grass
Potassium resides in the tips of growing grass, with Rye Grass, Clover and Lucerne normally 3-4% potassium. This can easily double when fertilisers are applied to enhance growth.
A horse's daily requirement of potassium is around 25g (up to 40g or 50g when in heavy work). However, with horses consuming approximately 2% of their body weight per day, a 500Kg horse can consume 10Kgs of grass/day, which means they can consume a whopping 300-400g of potassium/day! At the same time, as grasses become higher in potassium they do not correspondingly become higher in sodium; in fact, as grass gets high in potassium it is extremely low in sodium (0.02%).
Spring grass also has a higher water content which exacerbates the lack of sodium - that same 10Kgs of grass yields a mere 2g of sodium. Thus, actively growing grass means the horse is consuming too much potassium and too little sodium.
All the literature you read says that too much potassium is rarely a problem when the kidneys are functioning normally, as any excess is meant to be excreted in the urine, but ... horses on lush growing grass are flooded in potassium at the same time as being significantly deprived of sodium, and one of the important benefits of sodium is to encourage drinking, which encourages weeing, which will encourage excretion of potassium excess, so if sodium levels are low ... well, you get the picture.
This potassium:sodium ratio is really important, viz the grossly excessive potassium intake versus the seriously inadequate sodium intake. This is why also eliminating potassium-rich foods works immediately in most cases, i.e. lucerne/alfalfa, anything soya, seaweed/kelp, and oddly, molasses! (As if anyone reading this feeds anything molasses anymore anyway ROFL ...)
Eliminating any of these, and increasing sodium intake, can help bring the potassium:sodium ratio back to near-normal.
Just as we get our heads around it all, now we need to add in the Nitrate Factor
Actively growing grass also becomes high in nitrates. I know, minefield again. Which attach to potassium and go up into the plant with water. This is why horses can be worse after rain - basically the horse (or any grazing animal) is ingesting potassium-nitrate. And ... nitrates accumulate in cloudy weather and during night temperatures, which are too cool for growth, especially in cold, frosty weather.
The way the body gets rid of excess nitrates is via them attaching to calcium and magnesium and being excreted with these minerals. Thing is, this results in the horse's system then being rapidly depleted of calcium and magnesium, urggh!
Temporarily removing all greenstuff is the quickest way to get the potassium down, while feeding large doses of organic magnesium and salt to bring the other electrolytes up.
Typical signs of an excess potassium/lack of sodium imbalance :
Grass 'spikes' in potassium-nitrate under certain climate conditions, which occur mainly in spring/autumn but can be any time of the year depending on weather, which causes the electrolyte imbalance of too much potassium and too little sodium, calcium and magnesium. Ain't life great.
A quick mention on Staggers/Grass Tetany
Staggers is thought to be a classic condition caused by this imbalance. Progressive symptoms may include grazing away from the herd, irritability, muscle twitching, staring, incoordination, staggering, collapse, thrashing, head thrown back, and from then on it gets much worse. However, these clinical signs are not always evident before the worst conclusion.
The condition is said to result from hypomagnesemia (low magnesium concentration in blood) which can reflect low magnesium intake, low magnesium absorption, unusually low retention of magnesium, or a combination of these. The not so good news is that our UK grazing is nationally low in magnesium.
Let's start adding salt to the diet
The horse's self-regulating system can cope with balancing temporary spikes of potassium, but as mentioned above, our domestic horses are subject to permanent high potassium/low sodium diets, with the risk that the self-regulating system eventually becomes overwhelmed.
Adding a salt lick won't necessarily do the trick as horses have very soft tongues and a salt lick can be rough/course, so not all horses (mine included, no matter how I've tried) will lick them. Providing loose salt is also a bit risky as our temperate climate spoils it into a damp, unappealing clump, so you'll simply end up wasting it.
THE BEST WAY TO ADD SALT TO THE DIET, is literally to ADD IT TO FEED. Course salt is best, as this way the whole feed won't be tainted with the taste, just the occasional small crunch of it.
There are many varying recommended feed-rates out there, ranging from 8g/day up to a whopping 10g/100kg bodyweight per day, which I honestly think if I chucked in 50g for my Murphy, he'd likely give me the look that simply confirms that I'm the Devil's Child.
Personally? I go for a gently heaped tablespoon per day, aka a handful from the salt bag, and I double this on hot sweaty days or in hard work, although the latter doesn't really apply to my lot these days as we're all pretty much semi-retired now.
It goes without saying to add that when increasing salt intake, it's vital to ensure access to plenty of clean water.
Top Winter Tips
During winter our horses are at risk of winter colic - the diet is different, less grazing, more hay, and pipes freeze so troughs/water buckets are frozen or filled with freezing water which tends to be avoided.
Inadequate water is the leading cause of impaction, so keeping our horses hydrated in winter is really important to help prevent winter colic. Our horses need to drink at least 4 gallons of water a day, if not more, so we have to be ingenious to get them to drink.
PS - What about this apparent 'Hardening Arteries' risk?
It is not the salt that hardens arteries, rather it is a build up of calcium plaque which occurs because of giving calcium without balanced magnesium ratios. Horses are large animals and have a relatively large requirement for salt, especially when grass makes up a high proportion of their daily forage intake, if they are in hard work, or if the weather is hot.