Researchers have been focusing on certain factors that contribute to endocrinopathic laminitis (EL). As it turns out, horses and ponies that have more than one endocrinopathy occurring at the same time may create the perfect environment for more severe lamenesses.
The study “Phenotypic, hormonal, and clinical characteristics of equine endocrinopathic laminitis” was published in the January 2019 issue of the Journal of Veterinary Internal Medicine and conducted by Melody A. de Laat, Martin N. Sillence and Dania B. Reiche. The study was funded by Boehringer Ingelheim. A sample size of 301 privately-owned horses and ponies of various gender, breed and age were selected, each with a veterinarian’s diagnosis of laminitis or a history of such. Donkeys were excluded from the study.
Veterinarians were then asked to answer questions via an online questionnaire to create a profile for each horse or pony with owner consent. Questions covered the history of the equine, clinical examination findings, Obel grade of lameness, animal management and veterinary treatments in each case. Once the answers were logged, any identifying information was scrubbed to create unbiased results.
The equines were tested in the spring, and veterinarians submitted the measurements of each horse’s serum insulin and plasma adrenocorticotropic (ACTH) hormone concentration. In addition to these measurements, researchers also asked for additional submission data to ensure these horses were indeed suffering from EL, including a body condition score, a cresty neck score, regional adiposity description, a history of recent access to lush pasture, being a breed at-risk for equine metabolic syndrome (EMS), a history of being an easy keeper, a change in diet with increased nonstructural carbohydrate content without other signs of clinical gastrointestinal disturbance and other factors.
As a prospective cohort study, research was then conducted over a 2-year period. Each case of EL was categorized as being associated with either EMS, pituitary pars intermedia dysfunction (PPID) or equine Cushing’s disease, pasture consumption or any combination of the three. The data revealed that acute cases of laminitis occurred more often with EMS than with PPID or pasture-associated laminitis. However, insulin concentrations in those with both PPID and EMS were greater than in any of the three alone.
Insulin levels decreased as height at the withers increased, with breed having no effect on the levels. The data revealed ponies to have higher resting serum insulin than horses. Resting insulin serum concentrations were unaffected by the season or the gender of the equine. Seasonal changes did affect the levels of ACTH. In autumn, the levels were higher in ponies than in horses, much like the insulin concentrations. Size didn’t affect ACTH levels.
ACTH was used as a diagnostic tool to look for PPID. Higher levels of ACTH were noted in horses with PPID, as well as in older horses. The levels rose with the age of the equine. However, the levels were not affected by breed nor gender. The levels also did not vary greatly between horses with a history of laminitis and those without.
Radiographs were taken in just under half of the sample size. The most common finding within the images was evidence of rotation of the distal phalanx within the hoof capsule. Less common findings included decreased sole depth, distal displacement of the coffin bone, increased coronary extensor distance, evidence of gas within the soft tissues and osseous changes to the coffin bone.
EMS was the most prominent underlying disease noted in the study, followed by PPID. There was evidence of generalized and regionalized adiposity, both of which have been previously noted that there’s an increased risk of laminitis with the presence of fat deposits. By noting the correlation, it’s possible that by observing the adiposity early on, indicative of an underlying endocrinopathy, equine professionals can detect laminitis sooner to implement a management plan.
In looking at the data, researchers understand insulin concentrations can fluctuate, which other tests would have been beneficial to the study. Because the levels can change, insulin dysregulation could have been present in animals with PPID, which might have been another contributor to their lameness. When PPID and EMS are present simultaneously, the horse or pony displays higher insulin concentrations than those with only a single underlying factor. This is an important conclusion of the study because the higher the insulin concentrations, the higher the risk of laminitis. Insulin levels also positively correlated with the Obel grade of lameness, so those with higher concentrations are also more likely to suffer a more severe grade of laminitis.
Insulin concentrations were measured to be higher in shorter animals, such as the ponies, than in their taller counterparts. Insulin sensitivity seemed to decline with age. In comparing the average levels of insulin, equines were above the accepted level for EMS when samples were drawn at diagnosis. Then, after treatment or management, the average levels recorded were below the accepted level for EMS. While the exact factor is unknown, researchers can theorize possible causes. Certain clinical factors, such as pain, can influence bodily chemicals, including insulin. This theory then asks veterinarians to not only assess insulin levels but pain levels as well for more accurate results.
Clinicians should also educate horse owners about the necessity for early intervention not only for medical attention but for the comfort of the animal as well. Within this study, over half of the owners waited more than 10 days before calling the veterinarian. Owners failing to recognize the warning signs of early laminitis might be the cause more than consciously waiting.
The issue with EL is that when clinicians examine clinical or radiographical findings in a case of laminitis alone, EL is almost indistinguishable from other forms of laminitis. While EL is more likely to be chronic, the inciting causes remain similar. Equines with more than one endocrinopathy are more likely to suffer from hyperinsulinemia, which is a precursor to EL. Careful management of hyperinsulinemia is crucial to treating EL.
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