North American Veterinary Licensing Examination (NAVLE) Practice Test

The condition described, chronic laminitis combined with a long, thick coat in a horse, is most closely associated with Cushing's disease, also known as pituitary pars intermedia dysfunction (PPID). Cushing's disease is characterized by an overproduction of hormones from the pituitary gland, which can lead to a variety of symptoms, including the classic signs of a long, curly coat, which is a result of hormonal imbalances affecting the hair growth cycle.

In addition to the coat changes, horses with Cushing's often exhibit other signs such as lethargy, increased urination and thirst, and susceptibility to infections. The chronic laminitis mentioned in the question can be a secondary complication of insulin resistance, which is commonly seen in horses with Cushing's disease. Therefore, chronic laminitis and a thick coat together strongly suggest that the horse is experiencing the effects of Cushing's disease.

While the other conditions listed may also affect horses in different ways, they do not typically present with the combination of chronic laminitis and a long, thick coat as seen with Cushing's disease. Thus, Cushing's disease stands out as the most likely diagnosis in this scenario.