Nutritional Management for Metabolic Horses – Scientific Advancements

It is important to remember that what we know about equine nutrition is continually evolving as new research is published. An unfortunate pattern in the industry is the rise in equine obesity and metabolic disorders. Understanding how to optimally manage these horses is critical to their longevity and well-being.

This article will cover the up-to-date recommendations from recently published research. If you’re interested in reading more, I encourage you to take a look at the citations at the end of the article.

Understanding Insulin Dysregulation

When a horse is referred to as ‘metabolic’, it generally means that they have insulin dysregulation (ID). In these horses, their insulin is not effective at doing its job of moving the absorbed glucose from the blood stream into the tissues. When this occurs, the glucose level in the bloodstream does not return to normal and the pancreas releases large amounts of insulin to deal with the excess glucose load. This results in postprandial hyperinsulinemia, which is an exaggerated insulin response after a meal. Additionally, these horses will often have elevated insulin concentrations even without a previous meal.

When caring for a horse with ID, ensuring they maintain a healthy body condition while preventing exacerbated insulin responses is critical. Non-structural carbohydrate (NSC) content of a diet has been identified as a primary driving factor of postprandial hyperinsulinemia. Therefore, the NSC content is commonly discussed regarding the nutritional management of horses with ID.

What is Safe

When working with owners who have a metabolic horse, their most frequently asked question when it comes to hay, and feed is: ‘is it safe?’. The historical guideline of >12% NSC was extrapolated from research on PSSM horses, not metabolic horses. The study evaluated insulin responses to forages with varying NSC concentrations and found that high NSC forage produced higher insulin responses which could exacerbate PSSM symptoms.

Based on this, it was suggested that forage with >12% NSC could negatively affect horses with metabolic disorders. Recently, threshold studies with metabolic horses have been published which has provided clearer guidelines for what is safe for these horses.

Prior to this research, it was unknown how low the NSC content of a diet had to be to prevent the exaggerated insulin responses that metabolic horses have compared to healthy horses.

Dr. Erica Macon and her team completed work on possible NSC content threshold for ID horses. They found that these horses had a threshold of 0.1 g NSC per kg body weight (BW) per meal. Beyond this threshold, the ID horses displayed a significantly increased insulin response compared to the non-ID horses. Therefore, instead of relying on a percentage, calculating the grams per kg BW is recommended.

The NSC content of commercial products varies widely. There are ration balancers that are marketed as safe for metabolic horses and their NSC content is over 30%, whereas others are under 10%. With these new threshold studies, the NSC percentage must be combined with the amount being fed and your horse’s weight to determine if the product is safe or not.

Let’s use an example of a 500 kg horse that is fed a ration balancer once daily at the rate of 600 g.

Both ration balancers, when fed at the recommended rate for that horse are providing an NSC content above the safe threshold. Therefore, the meal size either needs to be reduced (fed in 2-3 meals instead of 1) or a lower NSC product must be used.

Here is the same calculation, but if the horse was fed 2 meals of 300 g instead of 1 meal of 600 g.

As you can see, ration balancer #1 would need to be fed over 3 meals daily to be within the safe threshold for that horse, whereas ration balancer 2 is considered safe if fed in 2 meals daily.

Now, that threshold information works very well for concentrates, but calculating the grams of NSC per meal does not work when we are feeding forage.

Currently, the science is limited, but it is recommended to feed forage that is less than 10% NSC on a dry matter basis. Research with ID equids demonstrated that processed forages (e.g., hay pellets or cubes) with less than 10% NSC could be suitable for horses with ID. In addition to the NSC content, it is hypothesized that implementing slow feeding strategies to reduce the rate of intake is likely beneficial for ID horses.

There are no studies that have evaluated how ID equids respond to different forage management strategies, but for healthy horses, it has been shown that when fed from a hay net, the peak insulin concentrations are lower than that of the horses fed off the ground. Additionally, it is well known that using slow feeders increases the consumption time.

More research is required to fully elucidate optimal hay management for ID horses.

Putting it Together

For obese metabolic horses, a forage that is less than 10% NSC on a dry matter basis with loose salt and a ration balancer or vitamin/mineral premix is recommended. The decision to feed a ration balancer fortified with protein, or to opt for a more concentrated source of vitamins and minerals will depend on the protein content of your hay. Ensuring that these horses are managed in a way to promote safe weight loss so that they can achieve a healthy body condition is critical.

Please note that when using a ration balancer, it still must not exceed 0.1 g NSC per kg BW per meal. An equine nutritionist can assist you in calculating this!

Insulin dysregulated horses that are lean, and need to gain weight, or do not maintain a healthy body condition on forage and a ration balancer should have calories added to their diet in the form of fat.

In senior horses, dentition can also be a key concern, so utilizing a low NSC complete feed and remaining conscious of NSC grams per meal is recommended.

Take Home Message

There is always more to learn with horses, and thanks to the many dedicated equine scientists – our understanding continues to grow. If you have a metabolic horse, I encourage you to take a deep dive into their nutritional management to ensure that it is following the latest guidelines. If you have any questions about this article, or your horse’s nutritional management feel free to reach out at balancedbaynutrition@gmail.com

By: Madeline Boast, MSc. Equine Nutrition

References:

Borgia, L., Valberg, S., McCue, M., Watts, K., & Pagan, J. (2011). Glycaemic and insulinaemic responses to feeding hay with different non‐structural carbohydrate content in control and polysaccharide storage myopathy‐affected horses. Journal of Animal Physiology and Animal Nutrition, 95(6), 798-807.

Carslake, H. B., Argo, C. M., Pinchbeck, G. L., Dugdale, A. H. A., & McGowan, C. M. (2018). Insulinaemic and glycaemic responses to three forages in ponies. The veterinary journal, 235, 83-89.

Frank, N., Bailey, S., Bertin, F. R., Burns, T., de Laat, M., Durham, A. E., … & Menzies-Gow, N. (2022). Recommendations for the diagnosis and Management of Equine Metabolic Syndrome (EMS). Equine Endocrinology Group.

Glunk, E. C., Hathaway, M. R., Grev, A. M., Lamprecht, E. D., Maher, M. C., & Martinson, K. L. (2015). The effect of a limit-fed diet and slow-feed hay nets on morphometric measurements and postprandial metabolite and hormone patterns in adult horses. Journal of animal science, 93(8), 4144-4152.

Glunk, E. C., Hathaway, M. R., Weber, W. J., Sheaffer, C. C., & Martinson, K. L. (2014). The effect of hay net design on rate of forage consumption when feeding adult horses. Journal of Equine Veterinary Science, 34(8), 986-991.

Kutzner-Mulligan, J., Eisemann, J., Siciliano, P., Smith, J., Hewitt, K., Sharlette, J., & Pratt-Phillips, S. (2013). The effect of different feed delivery methods on time to consume feed and the resulting changes in postprandial metabolite concentrations in horses. Journal of Animal Science, 91(8), 3772-3779.

Macon, E. L., Harris, P., Bailey, S., Barker, V. D., & Adams, A. (2022). Postprandial insulin responses to various feedstuffs differ in insulin dysregulated horses compared with non‐insulin dysregulated controls. Equine veterinary journal, 54(3), 574-583.

Macon, E. L., Harris, P., Bailey, S., Caldwell Barker, A., & Adams, A. (2023). Identifying possible thresholds for nonstructural carbohydrates in the insulin dysregulated horse. Equine Veterinary Journal, 55(6), 1069-1077.

Macon, E. L., Harris, P., McClendon, M., Perron, B., & Adams, A. (2024). Insulin dysregulated horses metabolic responses to forage pellets. Journal of Equine Veterinary Science, 133, 104991.