Introduction: What is laminitis?

Laminitis is an important health concern, especially during spring months when horses are given access to or are turned out on pasture. Laminitis is an inflammation of the laminae in the hooves, which is the tissue connecting the coffin bone with the hoof wall. When the laminae become inflamed, depending on the severity of the case, the coffin bone can rotate downwards. Complete downward rotation of the coffin bone is known as “founder.” Even if the case of laminitis is not so severe as to cause the rotation of the coffin bone, it may lead to lameness and other hoof health issues. Signs of laminitis in horses include, but are not limited to, a bounding digital pulse, “treading” where the horse is constantly shifting its weight between the left and right front foot, and reluctance to move especially on turns.

Pasture associated laminitis can be prevented by implementing pasture management strategies and the condition, if caught early, is somewhat treatable. Unfortunately, once a horse has had severe inflammation of the laminae, the damage is never completely reversed and that horse will be more likely to develop the disease in the future.

Figure 1. Source: http://www.thehorse.com/images/content/hoof_anatomy.html

What causes pasture associated laminitis?

When horses consume excessive amounts of sugars and starch, these carbohydrates pass though the small intestine (where they are normally digested with the help of enzymes) and spill over into the hindgut where they are rapidly fermented. Horses do not posses enzymes capable of breaking down fructans so they can pass through to the hindgut where they are also rapidly fermented by resident microflora. Rapid fermentation of carbohydrates in the hindgut results in the proliferation of lactic acid producing amylolytic and saccharolytic bacteria.  This may result in reduced hindgut pH, which in addition to hindgut acidosis, may lead to a cascade of events culminating in compromised blood flow (and thereby reduced nutrient supply) to the foot resulting in laminitis.

Laminitis is also associated with insulin resistance in equines, whereby the uptake of circulating glucose by tissue cells normally potentiated via insulin is reduced, leading to impoverished glucose supply to cells (or its metabolism within them), including those of the foot.  Insulin resistance is often seen in very fat horses and ponies, and may be exacerbated by high intakes of sugars and or starch.  While research has shown both digestive and metabolic forms of laminitis, the exact nutritional and physiological mechanisms are not completely understood. In either case, there is a clear link between the high levels of sugars in spring grasses and the resulting laminitis.

Management Solutions

The following are a few management tips that may help reduce the risk of pasture laminitis in horses.

1. When the time comes to reintroduce horses to pasture in the spring, do so gradually. By turning a horse out for small increments of time (15-30 minutes at first) and gradually working them up to full day turn out, they will be able to acclimate to the change in nutrients and will be at less risk of developing pasture associated laminitis.
2. If a horse is pre-disposed to laminitis (from previous occurrences or equine metabolic disease), then it may be a good idea to turn them out in the early morning or at night, especially during the spring months. One study found that sugar content is highest in the grass in the early evening and that it decreases to its lowest point in the early morning. This pattern was most prominent in April when compared to data from other months.³
3. Be sure to graze grass that is at an appropriate height. Overgrazing can result in horses eating the re-growth of the pasture. The new growth of grass usually has higher sugar content. On the other hand, if the grass stand in a pasture is overgrown or too mature, a horse may consume seed heads, which can also have high sugar levels.
4. Graze a horse with a muzzle on in order to reduce the amount of grass it is able to eat while still allowing for some exercise.

If a horse is pre-disposed to laminitis, for instance due to genetics (breed) or obesity, there are further steps that may need to be taken in order to reduce the possibility that the horse will experience laminitis. A webinar by Dr. Bridgett McIntosh, available through My Horse University, has several tips on managing a horse that may be more likely to develop laminitis.³

Conclusions

Pasture associated laminitis can be a serious problem and it is more commonly seen when pastures are lush and horses are transitioning back to grazing pasture after being inside or housed in a sacrifice lot and maintained primarily on hay. Some horses are especially sensitive to the sugar levels in lush pastures while others may not have a problem making the transition. It is important for owners to be aware of the management strategies that may help prevent laminitis, and to consult with their veterinarian concerning diagnosis and treatment.

Article prepared by: Sarah Thorne, Pre-veterinary and Animal Biosciences Honors Student, Susan Garey, Animal Science Agent, and Carissa Wickens, Assistant Professor and Equine Extension Specialist, University of Delaware

Article reviewed by: Bridgett McIntosh, Assistant Professor and Horse Extension Specialist, University of Tennessee

References and Further Reading

1. Wickens, Carissa and Stephanie Fraze. Equine Laminitis. September 2011. Accessed 12 April 2013: http://extension.udel.edu/equine/files/2010/07/EquineLaminitisFactSheet.pdf
2. Valberg, Stephanie, Peterson, Paul and Krishona Martinson. Founder and Spring Pastures. Accessed 12 April 2013: http://www.extension.umn.edu/forages/pdfs/Founder_and_spring_pastures.pdf
3. The Role of Nutrition in Horse Colic and Lameness. October 2011.  Accessed 12 April, 2013: http://www.extension.org/pages/12213/the-role-of-nutrition-in-horse-colic-and-laminitis
4. My Horse University. (21 April 2009). Countermeasure for Equine Laminitis [Webinar]. Accessed 11 April 2013: http://www.myhorseuniversity.com/resources/webcasts/equine_laminitis_april09
5. Rural Industries Research and Development Corporation RIRDC Newsletter. Pasture fructan concentration as a cause of equine laminitis. Journal of Equine Veterinary Science.  December 2004. 24 (12): 542.
6. Normal and Chronically Foundered Hoof Anatomy. Accessed 10 April 2013 : http://www.thehorse.com/images/content/hoof_anatomy.html