By Juliet M. Getty PhD

Horses are more likely to suffer from laminitis in the fall than any other time of year. There are two reasons: high NSC (non-structural carbohydrates) from cooler nighttime temperatures and increased blood ACTH (adrenocorticotropic hormone) secretion from the pituitary gland. Both of these lead to elevated insulin.

Insulin rise = laminitis


The laminae have two intermeshed layers, the epidermal and the dermal. When the epidermal layer lengthens and stretches with uncontrolled growth, it can weaken the laminae. This can lead to a structural failure by compromising the connection of the coffin bone to the hoof wall, creating a gap between the wall and the sole. You may see some hemorrhaging under your horse’s foot — an indication of laminitis.

Insulin also rises due to the normal hormonal cascade initiated by stress. Stress can take many forms. Intense exercise, mental discomfort, pain or an empty stomach (there should always be a steady flow of forage through the digestive tract) cause the pituitary gland to release ACTH.

ACTH signals the adrenal gland to produce the stress hormones cortisol and epinephrine, both of which are needed to release glucose for energy out of glycogen stores in the liver and muscle. Glucose from liver glycogen stimulates the pancreas to secrete insulin. The healthy body has a homeostatic mechanism to maintain these hormones within a normal range.

However, all horses — regardless of health status — experience a rise in ACTH between August and October (in the northern hemisphere). This seasonal rise can negatively impact the already insulin-resistant horse by further increasing inflammatory insulin, potentially leading to a laminitis attack.

NSC or ESC+Starch?



When these endotoxins reach the hoof, they themselves don’t really cause the problem. What happens instead is they cause an over activity of specific enzymes called matrix metalloproteinases (or MMP for short). These enzymes are important for normal tissue growth and repair, but when they become overactive, they are destructive, potentially causing laminitis. Consequently, it is important for the grass to have a low NSC (less than 12-13% on a dry matter basis) to avoid both endocrine-related and sepsis-related forms of laminitis.

NSC can vary with stress


Source: Dr. Juliet M. Getty

Safety guidelines:

  • When the nighttime temperature remains below 41° F (5° C) for 2 to 3 weeks, cool season grasses are high in NSC, even in the daytime. Wait until the base of the stems are no longer green. If they remain green throughout the winter, consider testing your pasture. Please see these two articles:
  • If the nighttime temperature remains above 41° F (5° C), the NSC will be lowest in early morning until approximately 10 a.m. and then again at night, starting a few hours after the sun sets.

Bottom line


[i] Adapted from two sources by Watts, Kathryn A.: (1) 2010, Pasture Management to Minimize the Risk of Equine Laminitis, Veterinary Clinics Equine, 26, 361-369; (2)  2004, Forage and Pasture Management for Laminitis Horses. Clinical Techniques in Equine Practices, 31(1), 88-95