Calcium for horses

Calcium in your Horses Diet

Nowhere will you find a bigger disconnect between nutritionists and biochemists than in the area of calcium. Nutritionists seem to have two major philosophies about calcium:
Calcium makes strong teeth and bones
- There needs to be roughly twice as much calcium in the diet as phosphorus

Calcium makes strong teeth and bones

This perfectly reasonable view is re-enforced by regulations that allow feed and supplement suppliers to make this claim without infringing veterinary medicines regulations. And 99% of the calcium is in your horses bones – so the other 1% can’t be very important. Never mind that 1% of the calcium in the body is far more calcium than appears to be important quantities of trace minerals like cobalt or selenium.

Beware the notion that strength in bones comes entirely from the mineralised calcium they contain. Drugs aimed at boosting bone density actually kill the important cells that regulate calcium movement in and out of the bone leading to densely mineralised bones that are actually as weak as piece of chalk. Some of us are old enough to remember just how frequently our teachers broke their chalk when writing on blackboards at school.

Instead we should think of calcium in bones more like the concrete in a modern concrete building. Without the steel reinforcing concrete buildings would be incredibly fragile. The living cells and protein structures in bones are like that steel. They contribute both strength and flexibility!

There needs to be roughly twice as much calcium in the diet as phosphorus

In the days when feed companies told us that cereal grains made great horse feed the base materials they used contained very large amounts of phosphorus. Without added calcium these grain based diets could cause problems like “bran disease” and lead to skeletal problems.

Modern diets are made from high fibre ingredients with much lower phosphorus contents. Yet the desire to add limestone (calcium carbonate) is still strong. While vets and some nutritionists are warning about the risks of kidney stones and the feed companies still add limestone. Most supplements companies use limestone as a carrier for their products assuming it is safe and has no negative side effects.

Bizarrely some of these same supplements firms are arguing against calcium based calmers on the basis of the dangers of limestone while chelated calcium calmers don’t have any limestone in them and the same supplements companies use it in great quantities in their own products. Kicking an own goal I think!


Calcium in cells

While the nutritionists are blinded by calcium in the bones the biochemists and physiologists have spent billions of pounds/dollars studying the half of one percent that floats around the blood and body fluids that performs the crucial role of switching cell functions on. The technical term is that calcium is a secondary messenger and it operates in electrically active cells – which is the vast majority of cells in the body.

So how does this work?

Apart from some calcium strategically located in stores within cells the inside fluids of the cells are virtually a calcium free zone. There are pumps in the cell membranes that do nothing but pump calcium out. This is actually a huge investment by these cells as the pumps are operating against a concentration gradient of about 1:30,000.

When the cell cytoplasm is calcium free the cell is in its resting state. So a nerve cell would not be sending messages and a muscle cell would be long and relaxed.

When the cell needs to fire a little burst of calcium ions is allowed in. It flows in very fast as the concentration gradient is huge. These calcium ions flick the switches inside the cell that make it work – nerve cells receive and send messages, muscle cells contract and hormone producing cells pump out their chemical messengers to the rest of the body. Cleverly some of the activated switches are on even more calcium pumps that expel the calcium ions very quickly and return the cells to their resting state.

While nutritionists are still thinking about calcium and bones the biochemists are only interested in its role in cellular signalling.


Calcium in the blood and the fluids that bathe the cells

The total amount of calcium in the blood is tightly regulated. The roles of Para Thyroid Hormone (PTH), Vitamin D and Calcitonin are quite well understood. We have even identified the protein that seems to measure the calcium in the blood. But we don’t yet seem to know how it measures that blood calcium.

Work carried out by a horse supplements firm strongly suggests that it is the total amount of calcium in the blood that is measured and regulated. This is really strange as the conventional wisdom tells us that only ionised calcium (see above for cellular signalling) is active. Surely if ionised calcium was all that mattered that is what would be regulated? And it is easy to measure ionised calcium. The biochemists have been doing it for years. It is far harder to measure total blood calcium. Yet this is exactly what the body seems to do. But these two charts of blood tests carried out a month apart on horses show that total is far more tightly regulated than ionised and this suggests that our current scientific understanding of blood calcium regulation is too simplistic.

So what forms does calcium take in the blood?

  • 55% of the calcium in the blood occurs as calcium ions. These come from the naturally occurring calcium in the feed and the limestone or calcium phosphate added to some feeds by feed companies.

Because the majority of recreational and competition horses around the world are on grazing soils that have a limestone base or are clays that derive from limestone, there is loads of calcium around to top up this ionised calcium in the blood. Even the small number of horses grazing calcium poor pastures seem to have little problem with providing enough calcium for cellular signalling purposes. An example is the best performing British horse at the Endurance World Championships in 2012 that had an ionised blood calcium level well below the normal range yet was clearly performing very well.

So it is likely that calcium supplementation by limestone is not required for any but a tiny minority of horses.

·    Protein bound calcium makes up approximately 35% of the calcium in the blood. This calcium is apparently bound up and unavailable for use anywhere in the cells. The amount of calcium bound to protein is normally quite stable but, if the horse gets ill or something boosts the levels of albumin (a protein that binds far more calcium than most) then the amount of calcium available to the animal (ionised) is apparently reduced.

  • The final 10% of calcium in the blood is bound to other chemicals. We can further split this group into two:

o   Inorganically complexed calcium which is bound to molecules like bicarbonate and maybe even undissolved calcium carbonate

o   Organically complexed calcium which is bound to sugars, amino acids and other molecules like gluconate, glycine and citrate.

These molecules are also generally regarded as inactive and yet the some people believe that these molecules are really important.


So how do these four components of blood calcium balance themselves out? It stands to reason that if the total amount of calcium is what is regulated then an increase in one component must be accompanied by a decrease in others.

If ionised calcium levels are high (horses grazing high calcium pastures and fed limestone supplemented feeds) then the space left for chelated (organically complexed) calcium is restricted. This would explain how that balance can be restored simply by adding chelated calcium to the diet. This would also explain why chelated calcium supplements are very popular in areas where soil calcium levels are particularly high.

In an attempt to discredit calcium calmers some supplement firms that are locked into magnesium have argued that calcium in excess is dangerous. This view is possibly valid when excessive limestone or calcium phosphate are involved. The targets of their ire should be feed companies and supplement companies using calcium carbonate as carriers or even ant-acids. Chelated calcium appears to be doing exactly the right thing and lowering excessive ionised calcium levels and replacing it with biologically active organically complexed calcium.

Further support for this theory comes from research in Australia. There are horses that are severely calcium challenged due to high oxalate levels in the pasture, these horses recover quicker when traditional limestone based supplements are removed and only partially replaced with chelated calcium than if the limestone is left in the diet.