Many horse owners choose to provide a salt block or salt lick, in effort to allow the horse to regulate his own salt intake. A plain (white) salt block only contains sodium chloride (salt; NaCl) and likely also some iodine. A trace mineral salt block (typically red or brown) also contains several of the trace minerals (such as copper, zinc, iron, etc.) that are required by the horse daily. Within trace mineral blocks, some also may contain selenium, and there are some differences among products, so be sure to read the label. Note that blue salt blocks contain cobalt, which is required for ruminants (and horses) for vitamin B12 (cobalamin) synthesis. Most red blocks also contain cobalt, however. Whichever you choose though, make sure you feed blocks that are designated for horses.
Salt and trace mineral blocks typically have consumption rates of about 50 grams per day, but this can vary widely between horses. As such, the intake of salt and minerals can vary widely. Some horses may only consume 15 grams per day, while others are known to munch away at a block within a few days. For straight salt, this wouldn’t be a problem, as long as the horse had good access to water and normal kidney function. If, however, high consumption rates are achieved with trace blocks, particularly those with selenium, the intake rates could become troublesome. For this reason, I also worry about the use of trace mineral tubs, where the trace minerals are mixed with molasses in effort to increase consumption rates. Certainly that might be required by some horses, but could also increase intake rates into unnecessary (and potentially dangerous) amounts.
It is wise for owners to monitor their horse’s intake of salt and/or trace mineral salt blocks – and if too much or too little is being consumed daily, owners should consider adding measured amounts in their feed tub daily. It may be difficult to monitor intake outside, particularly if several horses are kept together, but similar efforts should be made to ensure appropriate amounts are being consumed.
It should also be noted that if a horse is fed the required amounts of a commercial feed at the manufacturers’ recommended intake, he will already be consuming these trace minerals and salt that has been incorporated into the feed. No additional supplementation of salt is needed, therefore, particularly not a trace mineral block. A plain salt block may still be offered, but don’t be concerned if your horse doesn’t use it!
In summer months, warm weather and/or when a horse is working, electrolyte requirements will increase. Of the electrolytes, potassium (K) is often found in quite large amounts in good quality hay, but salt (NaCl) is usually low. Offering a salt block can, therefore, help a horse regulate his salt intake to some degree in lower efforts or temperatures, but during high intensity work, measured amounts of an electrolyte mix should be offered.
In the winter, there are no real changes in salt requirements. There are, however, sometimes changes in a horse’s water intake. So, make sure your horse is getting enough to drink, especially if he eats a lot of salt.
In the following examples), a 500kg horse at maintenance is consuming a basic grass hay with eight per cent protein. In Example A, the horse is offered 9.1kg of hay (1.8 per cent of body weight) and is offered a salt block, with expected average consumption of about 50 grams. As you can see, this salt consumption more than meets his requirements for salt, but because the hay lacks some of the other minerals, the diet would overall be deficient. In Example B, a basic trace mineral salt block is offered, again with an expected consumption of about 50 grams, and you can see it adds some important minerals, but is still deficient overall. A higher end trace mineral salt block with added selenium is shown in Example C. This one provides sufficient amounts of minerals for the horse, and excess selenium. Again, I would be concerned about over consumption to avoid selenium toxicity.
You will also note that in A, B and C, no vitamins have been added. If the grass hay was fresh, it is possible that it would still contain sufficient amounts of these vitamins, and if the forage was pasture instead (and the horses outside), then it would indeed contain sufficient amounts of vitamin A and E and the sunshine would provide vitamin D. In these scenarios with a hay that might have been stored for several months, additional vitamins would need to be added to the diet, however.
In Example D, a commercial feed was offered in recommended amounts. Using the lower end of intake suggestions, 2.5kg (0.5 per cent of body weight), and the hay had to be reduced to ensure the horse wasn’t over-consuming calories. In this example, he is eating 5.25kg (1.05 per cent of his body weight, which is approaching too little hay). Thanks, however, to the fortification of the commercial feed in minerals AND vitamins, you can see the horse does a much better job of meeting his needs with this diet, and does not need a salt or trace mineral salt block at all. Though, in this example, he still may need some selenium and vitamin E.
So, what is a good nutritional choice for salt vs a trace mineral salt? It truly depends. If a horse is at pasture 24/7 with no other feed, then a trace mineral salt choice is the way to go. You should, however, monitor consumption rates among horses. If the horse (at maintenance) is fed a commercial feed (ideally a more concentrated product to achieve lower rates of intake, resulting in being able to consume more hay!), then he shouldn’t need added salt, but a plain salt block is certainly fine to add to allow the horse to self-regulate his intake. If the horse has higher nutritional needs (due to work, pregnancy, etc.), a more thorough dietary evaluation should be conducted to ensure that all nutrient intakes are being met.