Mineral Blocks for Mules

One equine nutritionist explains why mineral blocks might not be ideal for mules, and what can replace them.
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Salt blocks might be a better alternative to mineral blocks for mules. | The Horse Staff

Q. We recently purchased a mule, and I have provided him with free access to a mineral block designed for horses. Are there any concerns with allowing the mule free access to the mineral block? He doesn’t really lick the block but bites chunks and eats them. Should I limit his access? Is this safe for him?

A. Although similar to horses, many mules are more efficient with calories and protein. This is often why they tend to be overweight – because they are typically housed with and fed the same as horses.

A mineral block is a source of vitamins and minerals; however, trace mineral salt blocks are often primarily salt and contain minimal quantities of trace minerals. Therefore, it can be very challenging for a mule to consume adequate amounts to meet their requirements. Additionally, intake from these blocks can be extremely difficult to quantify, so it is challenging to definitively determined if your mule’s nutrient requirements are being met.

Nutritionally, it is unlikely your mule is consuming enough salt or other minerals to cause toxicity symptoms. However, it is possible—although extremely rare—for equids to develop salt toxicosis. Oftentimes, for toxicity to be an issue, the supplemented level must be extremely high. For example, with selenium, a 1,100-pound equid consuming 2% of its body weight in dry matter would have an upper safe limit of 20 milligrams per day before toxicity symptoms would potentially occur. To put this in perspective, the NRC (Nutrient Requirements of Horses) recommends 1-1.25 milligrams/day for a 1,100-pound horse. Therefore, nutritional toxicity is extremely unlikely; however, other health concerns could explain or account for that behaviour.

The other concern with biting the block and eating chunks is it could result in dentition or jaw issues. The biting of blocks could indicate nutritional deficiencies or frustration around not being able to consume adequate amounts. It is important to note these blocks were originally designed for cattle that have much rougher tongues, so your mule might be struggling to consume enough.

The gold standard recommendation is to provide mules with their required vitamins and minerals in their diet, then simply allow the additional salt block to be free choice. You can achieve this by feeding your mule a low-calorie ration balancer, which will provide a concentrated source of vitamins and minerals without adding unnecessary calories to the ration. When feeding a ration balancer, it is also recommended to add loose salt to their meals. For a 1,100-pound equid at maintenance, nutritionists recommend adding about 2 tablespoons (1 ounce) of loose iodized table salt per day to the ration, along with a free-choice source.

You could switch your mule’s block to a plain salt lick or even provide him with loose salt instead of a block. Monitor his intake and see if, with a properly balanced ration, he is still consuming large amounts of salt. If he still tends to bite the block and consume large amounts, it would be helpful to discuss the potential health concerns with your veterinarian.

Overall, to better meet your mule’s nutritional needs, switch him from a free-choice mineral block to a low-calorie ration balancer. When feeding a ration balancer, be sure to follow the manufacturer’s feeding instructions or consult a qualified equine nutritionist. Add loose salt to the ration and provide him with free-choice access to a plain salt lick or a dish of loose salt. Be sure to monitor him closely to see if his tendency to bite the block decreases when his nutritional needs are met through a ration balancer.


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Madeline Boast completed her master’s in Equine Nutrition at the University of Guelph and started an independent nutrition company known as Balanced Bay. She has worked with a variety of equids—from Miniature Ponies to competing Thoroughbreds. Boast designs customized balanced nutrition plans that prioritize equine well-being, both for optimal performance and solving complex nutritional issues and everything between. 

One Response

  1. I quit feeding selenium-vitamin e to my mules when one developed loose mane hair and holes in her hoofs. She has improved. Since then I have been feeding 3 vitamin e (human) 600 iu gel tabs daily, as I have no pasture with purchased hay bales.

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