By Brenda Jackson, UGA Extension, Murray County; and Dr. Kylee Jo Duberstein, Professor, Equine Science, Department of Animal and Dairy Science
Laminitis is a painful and debilitating hoof condition that results from a variety of nutritional, health, and environmental factors. Since pasture-associated laminitis is one of the most prevalent forms of laminitis, it is worth discussing this topic in relation to summer when grass is prolific and horses tend to gain weight. As background information, laminitis specifically refers to inflammation of the laminae of the hoof and is typically divided into stages. Another commonly used term, founder, is a potentially severe outcome of laminitis and involves displacement of the coffin bone in the hoof as it begins to rotate or sink within the hoof capsule (Figure 1). Not all laminitis cases involve displacement of the coffin bone, and therefore it is important to seek veterinary assistance as soon as laminitis is suspected because prompt treatment can mitigate damage to the hoof, displacement of the coffin bone, and improve the horse’s long-term prognosis and outcome. In an active laminitis case, a veterinarian will perform diagnostics including radiographs of the hoof to assess the position of the coffin bone in relation to the hoof capsule, and form a treatment plan to manage inflammation and stabilize the coffin bone.
Table of Contents
Stages of Laminitis
- Developmental – The developmental phase of laminitis occurs after exposure to a causative agent or event. During the developmental phase, the horse does not show clinical symptoms of laminitis. However, pathological changes to the laminae of the hoof may begin to occur.
- Acute – Lameness signs begin within hours or days due to acute inflammation in the hoof. Symptoms include an increase in the horse’s digital pulse and potential heat in the hooves. Any swelling will be internal and therefore not visible. Laminitis more commonly affects the front hooves, so the horse may display a “laminitic stance” where they shift weight off the front feet; it might appear as if they are “rocking” back and forth or standing with all their weight on the hind limbs (Figure 2). Depending on severity, the horse may be unwilling to walk/move or rise from a laying position. In severe cases, inflammation in the hoof will cause weakening in the structure of the laminae which allows the coffin bone to rotate or displace from normal position. It is important to note that while laminitis is more common in the front hooves, which leads to the classic rocked back stance, the hind hooves can be affected in addition to the front hooves, and less frequently, laminitis can occur in the hind hooves alone which can lead to different lameness symptoms.
- Chronic – Long term damage to the hoof structure is referred to as chronic. Displacement of the coffin bone can be measured on radiographs. Outwardly, the hoof may start to take on a dish appearance in the hoof and ridges may be observed on the wall of the hoof as it begins to grow out from the coronet band. Chronic damage to the hoof often requires specialized farrier treatment and in severe cases can be fatal.
Causes
The acute tissue inflammation in the laminae of the hoof is what causes the pain associated with laminitis, which can range from mild soreness to severe separation of the coffin bone. Causes of laminitis vary and can be classified into three main types: (1) supporting limb laminitis, (2) sepsis or systemic inflammatory response syndrome (SIRS), and (3) endocrinopathic laminitis. Supporting limb lameness is not typically associated with nutrition and involves laminitis developing in the contralateral limb following an injury that reduces weight bearing on a limb. Laminitis due to SIRS involves a precipitating event that causes systemic inflammation in the body which then results in laminitis secondary to the original condition. Examples of conditions that may trigger SIRS include colitis, metritis, and pneumonia. Nutritionally, a large intake of rapidly fermentable carbohydrates (i.e., classic case of the horse getting in the grain bin and gorging) can cause a rapid drop in hindgut pH which results in hindgut dysbiosis (disruption of bacteria in the hind gut) and endotoxemia (toxins in the bloodstream) which can cause laminitis that fits this SIRS category. Finally, the most prevalent category of laminitis is endocrinopathic laminitis, of which most cases involve insulin dysregulation in horses. It has been reported that endocrinopathic laminitis may account for as many as 90% of laminitis cases in horses. The two conditions most associated with insulin dysregulation and laminitis in horses are equine metabolic syndrome (EMS) and pars pituitary intermedia dysfunction (PPID).
PPID is a condition associated with aging in horses (typically found in horses >20 yrs of age) and involves degeneration of dopamine producing cells in the hypothalamus of the brain which results in enlargement of the pituitary. This disorder can cause a host of secondary conditions, of which insulin dysregulation and laminitis are common. Prescribed medication can be helpful in treating horses with PPID that may be prone to laminitis, so consulting with your veterinarian is recommended and may prevent laminitis episodes in affected horses. EMS is another condition that is commonly associated with laminitis. EMS is simply insulin dysregulation that is not caused by PPID. EMS is most commonly seen in horses with prolonged obesity and is often exacerbated by diets that are high in non-structural carbohydrates (NSC, a term that encompasses the sugars and starches in the diet). Pastured horses are often at risk of developing EMS due to multiple factors. Firstly, high quality pastures often provide the opportunity for unlimited grazing and therefore overconsumption of calories is needed to maintain body weight. Secondly, many pastured horses are not regularly ridden and therefore are more apt to gain weight. And thirdly, pasture grasses, especially during certain times of the year, have high NSC levels which can further drive insulin dysregulation.
Insulin dysregulation can trigger laminitis under certain conditions. In a healthy individual, consumption of NSC results in an elevation in blood glucose levels as the body breaks down and absorbs these carbohydrates. The elevation in blood glucose levels signals the pancreas to release insulin which then binds to cells throughout the body to move glucose out of the bloodstream and into cells. Following the movement of glucose into cells, blood levels of glucose and insulin drop. When an insulin-dysregulated horse consumes a high NSC diet, the process begins the same in that blood glucose levels are elevated, and the pancreas is signaled to release insulin. However, while insulin levels in the blood stream are elevated, the cells do not efficiently bind insulin and move glucose into the cells. This results in elevated levels in the blood of glucose (hyperglycemia) and insulin (hyperinsulinemia). Hyperinsulinemia is a recognized trigger of laminitis.
Laminitis Prevention
The prevention of laminitis involves proper hoof care as well as both health and weight management. It is recommended to conduct daily hoof inspections in order to notice changes that might indicate the development of laminitis. Have regular farrier visits to ensure hooves are balanced appropriately and healthy. Store grain securely so horses cannot get into it by accident, and practice good pasture and stable management to prevent access to environmental toxins. For high-risk horses (those that have had laminitis episodes in the past or are insulin resistant) ensure they have a balanced diet that limits NSC. Since elevated blood glucose levels drive hyperinsulinemia, try to provide calories from fiber rather than sugar/starch to horses that are insulin dysregulated.
It is also important to recognize that prevention of laminitis involves maintaining horses at a healthy body weight. Body condition scoring horses should be a routine management practice implemented on horse farms. Obesity is a driving factor in the development of insulin dysregulation, so prevention of pasture associated laminitis relies on preventing obesity and restricting access to grasses during times of the year when NSC levels are elevated. In general, cool season grasses (those that grow during the spring and fall months) have higher NSC levels as compared to warm season grasses (those that grow during the summer). However, during the summer, even though NSC content of grasses may be lower, there may also be an abundance of grass that can drive weight gain and further exacerbate insulin dysregulation. Therefore, it is important to manage (restrict) intake of horses that are (1) overweight and on free access to pasture and (2) at risk for laminitis (due to insulin dysregulation) and on a pasture with high NSC levels (typically during the spring and fall). Restricting grazing typically involves either removal from pasture (e.g., housing on a dry lot, stall, or pasture track) or use of a grazing muzzle when the horse has free choice access to pasture. It is important to recognize that intermittent muzzling for only part of the day is not typically effective. A muzzle reduces the amount of forage the horse can consume per bite and therefore reduces intake. However, as soon as the muzzle is removed, many horses will compensate by eating more than they typically would in a shortened time interval. Therefore, the horse must either be fitted with a muzzle that is comfortable enough to be worn continuously, or it must spend at least part of its day in a dry lot or stall if the muzzle is to be removed during the day. Please note that not all pasture horses need this type of management! Horses that are in a healthy body condition and do not have metabolic disorders (such as insulin dysregulation) are typically fine to free choice graze in a pasture setting! Make sure you learn how to properly body condition score your horse prior to making changes to its diet!
Laminitis Treatment
For a horse with laminitis, treatments will vary by veterinarian and animal, usually in response to the severity of the diagnosis. Initial treatment will revolve around minimizing progression of the disease – pain management and supportive care until inflammation subsides. It is important to identify the inciting factor and eliminate that to prevent recurrent episodes and then work to prevent further damage to the laminae while maintaining blood supply to the hoof. Acute laminitis treatment often includes:
- Stall rest with deep bedding
- Non-steroidal anti-inflammatories (NSAIDS)
- Cold therapy – either a cold-water hose, ice bath or “ice boot”
- Farrier treatment to support the coffin bone and encourage normal hoof growth
- Dietary management to minimize NSC and limit access to lush pasture
If laminitis is caught early, the severity may be minimized. The outcome will depend on the severity of acute inflammation and displacement of the coffin bone (if any). Prevention of laminitis requires minimizing risk factors, and in many cases, paying close attention to the horse’s diet. Since the majority of laminitis cases are endocrinopathic in nature and typically involve insulin dysregulation, it is critical to manage the horse’s diet to keep the horse at an optimal body condition score. Additionally, owners should work with their veterinarian to diagnose any underlying conditions that may lead to insulin dysregulation. For horses that are insulin dysregulated (this can be determined by your veterinarian), it is often recommended to restrict NSC levels in the diet to approximately 10% (e.g., provide forage and concentrates that have an NSC of 10% or lower). Your county extension agent can assist you with learning how to body condition score your horse as well as testing forage and feed for NSC levels.