It’s a perennial question. Can a horse meet his salt needs from a salt block? In a way, it’s a trick question. There is more than enough salt there to meet the horse’s needs. The real question is will the horse consume all he needs from a block.
While horses can, and do, lick salt blocks it may not be enough
A widespread myth is that horses cannot get enough salt from a lick but cows can because their tongues are rougher. A cow’s tongue is rougher (like a cat’s) – but not rough or sharp enough to slice salt off a block! Cows and horses both get salt from a block by dissolving it with their saliva. Same as licking a lollipop.
All herbivores have a strong drive/taste for salt. The sodium in salt (salt is sodium chloride) is the only mineral consistently at very low levels in the natural diet. The drive to eat salt comes from the brain. Salt hunger increases with higher levels of the hormones aldosterone and angiotensin II. The main function of this hormone system is to regulate blood pressure and maintain normal blood volume. Sodium is important for this because of the major role it plays in holding water in the blood stream and the tissues surrounding the body’s cells.
Both horses and cows prefer loose, coarse salt over salt blocks but are able to meet their needs using a block when at maintenance or even lactating. Factors that may cause a horse to overeat salt are individual taste preference or boredom. For example, stalled horses eat less salt if they have a toy to play with. Insufficient consumption may be influenced by gum disease, oral ulcers or oral irritation from abrasive plant material.
Mild overconsumption (about twice requirement) has been documented in horses and has no negative consequences. Failure to eat enough salt can also occur, even at maintenance. If you are unsure if your horse is eating enough salt from a block, you need to weigh the block every few days and compare consumption to need. See https://wp.me/p2WBdh-Ao.
Studies have shown horses with large sodium losses through sweating are the least likely to meet their daily needs with voluntary salt intake. There’s a reason for this.
It has been claimed that horses can regulate their salt intake to match their needs. This is actually what the aldosterone-renin-angiotensin system attempts to do. However, the focus is not on sodium per se. It’s on blood volume and blood pressure.
When a horse produces sweat it pulls the water and electrolytes needed from the blood stream. To rapidly replace those losses, water and electrolytes are moved into the blood from the cells and tissues surrounding them. Important factors here:
- The regulatory system only responds to blood levels
- Once blood levels are restored, the body thinks all is well even if tissue and cellular levels are still low
- Equine sweat is more concentrated in electrolytes than blood is
The end result is blood restored to normal but tissue electrolyte and water levels still low. Since the horse has no drive to eat more salt or drink more water when blood levels are normal, this deficiency persists. If the horse does not have any further large sweat losses the fluid and electrolytes will eventually equilibrate if the horse has access to extra salt but this process can take several days, not a good scenario for horses in regular work.
The bottom line is that horses doing no or only very light work may meet their needs from a block but you have to measure to make sure. Horses that are exercising and losing significant amounts of water and electrolytes in sweat will need supplementation if in regular work.
Eleanor Kellon, VMD