How Does Laminitis Develop?

Laminitis is the term used for the loss or damage to the lamellae in the hoof 1. The lamellae are structures that connect the hoof bone and the hoof wall. When there is damage to or a decrease in the lamellae structures, laminitis can develop. Laminitis can be caused by several factors, but the three most common causes are sepsis due to other diseases in the body, such as (chronic) infections, excessive weight bearing, or endocrine (hormonal) disorders 2.

Sepsis can occur when an inflammatory reaction takes place in the body due to pathogens, toxins, or poisons circulating in the body 3. Horses can ingest toxins from poisonous plants or contaminated drinking water. Toxins can circulate in the body when bacteria in the intestines die off due to a diet containing excessive amounts of non-structural carbohydrates. When the diet contains too much non-structural carbohydrates, they pass through the stomach and small intestine, eventually reaching the large intestine, where they are fermented by the hindgut microbiome. This creates an acidic environment in which the bacteria, that are part of the hindgut microbiome cannot survive and therefore die off, releasing toxins 4. Since the acidification of the intestines also damages the intestinal wall, these toxins are absorbed into the body, circulating throughout the system, eventually reaching the lamellae and causing damage that leads to laminitis 5.

Laminitis due to excessive weight bearing on one limb, also known as support limb laminitis (SLL), occurs least frequently in horses. This can occur, for example, when a horse is lame in one leg and cannot distribute its weight properly over the other legs. As a result, excessive weight is placed on one leg, overloading the hoof and disturbing blood circulation, which affects the lamellae 6.

The most common form of laminitis is caused by hormonal and metabolic disorders such as Equine Metabolic Syndrome (EMS) and PPID, with the development of Insulin Resistance (IR) being the most common cause of laminitis 7.

Insulin Resistance is a metabolic problem where the body no longer responds to insulin. Insulin is a hormone that regulates blood sugar levels in the body. When a horse eats a meal containing a high amount of non-structural carbohydrates (starch and sugar), the blood sugar level rises. Insulin then ensures that the body is stimulated to absorb the carbohydrates, which have been converted into glucose by the digestive system, lowering the blood sugar level 8. If the blood sugar level remains elevated, insulin continues to be produced, and the body becomes less sensitive to the hormone, requiring higher concentrations before the body responds 8. This means the body becomes resistant to insulin.

Constantly higher insulin concentrations in the body increase the risk of developing laminitis 8. Studies suggest that insulin resistance can cause blood vessels to constrict, which affects the blood supply, including to the hooves, potentially leading to an oxygen deficit 9. This has a negative effect on the lamellae, ultimately resulting in laminitis.

Laminitis can be acute or chronic. Acute laminitis occurs suddenly, and it is important to treat the horse as quickly as possible 2. In chronic laminitis, the hoof bone begins to separate from the hoof wall, and in severe cases, the hoof bone may completely detach, rotate, and potentially penetrate through the sole of the hoof 2.

The symptoms of laminitis arise due to the pain of the condition. Horses may take shorter steps or limp. Some horses shift their weight from foot to foot. Additionally, horses may refuse to move or lie down a lot. An abnormal stance is another symptom of laminitis where horses position their front legs far forward and tuck their back legs under their body, trying to relieve pain from the front feet. Laminitic hooves also feel warm to the touch. 

Treating Laminitic Horses

If a horse or pony shows the above symptoms, it is important to consult a veterinarian as soon as possible. The treatment of laminitis varies depending on the cause and severity of the condition. A veterinarian determines the severity of the laminitis by taking an X-ray of the hoof. If necessary, the horse will be given medication to manage the pain and reduce any inflammation 10. Cooling the hoof can also help alleviate pain. Especially when the cause of laminitis is related to metabolic issues, it is most important to change the diet.

Diet for Horses with Laminitis

Diet plays a significant role in (endocrine) laminitis. Therefore, it is important to adjust the diet when a horse is diagnosed with this form of laminitis. 

To support the horse and as part of the treatment, the diet of horses with endocrine laminitis should contain as little sugar and starch as possible. It is advisable to feed these horses a diet that contains less than 10% sugar and starch 11. This means that these horses should not graze on fresh grass, and any feed provided alongside forage should have a low sugar and starch content 12.

It is important to ensure the horse receives enough high-quality forage, approximately 1.5 to 2% of the horse's body weight in kilograms of forage, with a sugar content below 10% 11. When purchasing hay, ask for a forage analysis or carry out a forage scan to ensure that the forage contains minimal sugar and starch, which is suitable for a restricted diet.

If the horse requires extra energy, for example, for exercise (if possible), beet pulp (with low sugar and starch content) and linseed oil can provide the necessary energy. Beet pulp is a forage that is converted into volatile fatty acids in the intestines, supplying energy to the horse. Linseed oil is a plant-based oil that provides a long-term form of energy. Feeding these products ensures enough energy is available for the body during exercise without adding excessive amounts of sugar and starch to the diet.

Forage alone does not provide enough vitamins and minerals to meet the horse's daily requirements. Therefore, balancers or vitamin and mineral supplements (also with a low sugar and starch content) are added to the diet. These contain all the essential vitamins and minerals in the right amounts to meet the horse's daily nutritional requirements.

When selecting feed for horses with laminitis, it is important to check the labels carefully and verify how much sugar and starch the feed contains. If in doubt, consult a nutritionist who can assist in creating a suitable diet plan for your horse.

Prevention

A proper diet helps prevent the development of endocrine laminitis. Metabolic disorders such as IR primarily arise in horses fed a diet too high in sugar and starch. These horses often also have an excessively high body condition score (BCS).

Monitoring the BCS ensures that you can identify when your horse is consuming too much energy through its diet. If the BCS is too high, this indicates that the diet and energy intake need to be adjusted to prevent obesity and IR, thus reducing the risk of developing laminitis. 

Additionally, it is essential to carefully manage the grass intake of horses, particularly those sensitive to laminitis, during the spring. This is especially important when transitioning from a sand paddock to a grass field to prevent them from ingesting too much fructan. For more information, read the blog on regulating grass intake in horses.

Good nutrition is crucial for the health of the horse and to prevent conditions such as laminitis. If you're unsure whether you are feeding your horse the correct diet, consult a nutritionist who can help you create an appropriate diet.

References

1. Patterson-Kane, J.C., Karikoski, N.P., McGowan, C.M. (2018) Paradigm shifts in understanding equine laminitis. The Veterinary      Journal, 231:33-40.

2. Marcato, P.S., Perillo, A. (2020) Equine Laminitis. New insights into pathogenesis. A review. Large Animal Review, 26(6):353-363.

3. Eades, S.C. (2016) Chapter 22- Sepsis-related Laminitis. In: Belknap, J.K. & Geor, J. Equine Laminitis. John Wiley & Sons, Inc: Amerika.   

4. Belknap, J.K., Black, S.J. (2012) Sepsis-related laminitis. Equine Veterinary Journal, 44:738-740.

5. Bailey, S.R., Baillon, M.L., Rycroft, A.N., Harris, P.A., Elliott, J. (2003) Identification of Equine Cecal Bacteria Producing Amines in      an In Vitro Model of Carbohydrate Overload. Applied and Environmental Microbiology, 69(4):2087-2093.

6. van Eps, A., Collins, S.N., Pollitt, C.C. (2010) Supporting Limb Laminitis. Veterinary Clinics of North America: Equine Practice, 26(2):287-302.

7. de Laat, M.A., Sillence, M.N., Reiche, D.B. (2019) Phenotypic, hormonal, and clinical characteristics of equine endocrinopathic      laminitis. Journal of Veterinary Internal Medicine, 33(3):1456-1463.

8. Kaczmarek, K., Janicki, B., Glowska, M. (2016) Insulin resistance in the horse: a review. Journal of Applied Animal Research, 44(1): 424-430.

9. de Laat, M.A., Sillence, M.N. (2020) A review of recent developments in the pharmacological prevention and treatment of            endocrinopathic laminitis. Animal Production Science, 60(18):2111-2121.

10. Laskoski, L.M., Valadão, C.A.A., Dittrich, R.L., Deconto, I., Faleiros, R.R. (2016) An update on equine laminitis. Clinic and Surgery, 46(3):547-553.

11. Menzies-Gow, N.J. (2010) Endocrinopathic Laminitis: Reducing the Risk Through Diet and Exercise. Veterinary Clinics of North       America: Equine Practice, 26(2):371-378.

12. Cohen, N.D., Gibbs, P.G., Woods, A.M. (1999) Dietary and other management factors associated with colic in horses. Journal          of the American Veterinary Medical Association, 215(1).