Overfeeding: The Danger It Could Have for Horses

Last Updated on November 10, 2020 by Allison Price

Equine Feeding Management: The How & When of Feeding Horses | Animal & Food  Sciences

Too much of everything may lead to serious problem. Horse owners aim to have a good and healthy horses. They want them to stay strong as long the horses can. When horses have illnesses horse owners want them to heal as soon as possible. Thus, in this moment, the problem begins. 

You tend to rush everything not minding the possible effects of too much nutrients intake of your horses. There are guidelines for to follow whether your horses are in good or bad condition. You think that you are giving the right way but it could lead to clinical health problems. The sick horses might not be able to recover if proper guidelines are not followed. Instead of leading them to recovery, it goes on the other way around. Same goes with those horses that are healthy, they are prone to sickness when the amount of nutrients is above the maximum level. Symptoms might not show in an early stage but on the latter your horses will be victimized of toxicity.

What are the nutrients that need to be observed? What are the possible effects of those excessive nutrients to horses?

Let’s Get Started!

Some issues cause of over-feeding of feed supplements

Some horse owners feel that what they are giving to their horses are not enough. They will often say that it is better to have more than to have less. With this, they tend to give beyond the prescribed feed supplement intake for horses. According to experts, this practice is a common misconception and might lead to serious health problems of horses. Also, they failed to understand that even if the supplement is not toxic in large amount. Horses should double their hard work to be able to process the excessive nutrients that is given to them. 

According to research, vitamin A is given to horses by their owners without considering the prescribed amount of it. As a result, they always experience problems about their horses because of their carelessness. Moreover, excessive vitamin A will hinder the growth of young horses and bone development. It can also lead to various skin conditions to young horses. 


The nutrient that most often fed to the horse in an excessive amount is the protein. Most horse owners made the protein and its building blocks as support to muscles. However, giving a lot of protein to horses may damage their kidneys and can cause strains on horses’ body. 

Moreover, as you increase the amount of protein, the amount of ammonia increases. As a result, your horses may slow down in a race. According to research, the ‘per kilogram’ of protein can slow down the racehorse from one to three seconds. The researchers suspect that the body fights ammonia caused by too much protein. Also, the excessive ammonia content in the horses’ urine may lead to respiratory disease, eye irritation, and hoof problems.


Selenium has a tendency to reach to its toxic as fast as it can. According to some researchers, the prescribed content of mineral should be one to three ppm or parts per million. The 18 parts per million of minerals is already toxic for horses. Moreover, feeding different supplement that contains selenium could increase its level. It could also be dangerous to horses if they are in an area where soil is abundant with selenium.

It is okay to feed your horses with couple of supplements if you are in an area where selenium is low. The toxicity happens when your area has high selenium in soil and your horses diet has high selenium level. The first symptoms that you can see to your horses is the loss of tail and mane hair. In some cases, your horses may lead to euthanize cause of uncontrolled selenium intake. 

Another overfed mineral is the magnesium. This mineral can calm your horses and some horse owners use this to control the unwanted behavior of horses. Magnesium can be found in various substance and there are forages that contain high magnesium. Even though there are no clear toxic effects of this mineral in horses, other data from other species show it. They showed clinical symptoms like loose of teeth, weight loss, and development of orthopedic disease. 

Copper and zinc are part of those minerals that should be given concern by the horse owners. These minerals should be given in balance. Feeding your horses with too much of one of these minerals may deficient the other. Also, calcium and phosphorus should be fed in ratio to avoid deficiency and other serious problem. In the future, if you will bump into problem with high metal toxicity, investigate the environment. Pollution from industries or contaminated water that creeps into the pasture may be the source of the problem.

Vitamin A

The safe level of vitamin A for the horses to take is about 16,000 IU per kilogram. This will allow the supplement to take place in the storage of the liver without saturating it. There are few horses that will show symptoms cause of excessive amount of vitamin A until it reached to 100 times upper from safe level. Excessive amount of vitamin A will cause abnormal bone growth, bone fragility, decreased blood clotting, scale skin, and poor hair coat. These are known cases of vitamin A toxicity caused by giving more supplements than the usual. 

Vitamin D

Vitamin toxicity cause by vitamin D is the most common problem of horse owners. The safe level to prolong the feeding of vitamin D supplements is 2, 200 IU per kilogram for the overall diet. The symptoms of vitamin D toxicity includes weight loss, lower feed intake, lower activity level, and high blood phosphorous concentration. The symptoms might worsen to the extent that your horses will always lie down and will experience seizures. 

Vitamin E

According to studies, they could not find definite proof of vitamin E toxicity. However, it could prevent other fat-soluble vitamins to be absorbed by the horses’ body. About the level of 4, 500 IU per kilogram is being fed to performance horses with no side-effects. However, there is no definite evidence that can prove the need for this high level of vitamin E.

Vitamin K

Moreover, there are three variations of vitamin K – K1, K2, and K3. The common form that is most available in the commercial horse supplements is the K3. It is water soluble and do not have any risk. However, injecting your horses with 2mg per kg of their body weight will lead to death and acute renal failure.

For your to be more knowledge about overfeeding, watch this video:

Take Home Message

Not everything beneficial is good. Everything has limitations. An excessive amount of different supplements given to your horses might lead to a serious problems and may lead to death. It is better to study more about the nutritional requirements of your horses. Research more about the minimum and maximum level that is allowed for your horses to take. Moreover, it better to reach an expert if you are having a hard time understanding various explanations in a book or other related materials. It is better to be extra careful since you are domesticating such animals.

Allison Price
Allison Price

I’m Allison, born and raised in San Diego California, the earliest memory I have with horses was at my grandfather’s farm. I used to sit at the stable as a kid and hang out with my Papa while he was training the horses. When I was invited to watch a horse riding competition, I got so fascinated with riding!