Date of Award

Spring 1980

Project Type

Dissertation

Program or Major

Zoology

Degree Name

Doctor of Philosophy

Abstract

Laminitis, an inflammation of the lamina in the equine foot, is one of the least understood of the common equine diseases and is considered to be one of the greatest problems facing the horse owner and veterinarian today. The incidence of, and breed susceptibility to, this disease has never been formally assessed. Many practitioners feel that susceptibility may be related to metabolic imbalances. The purpose of this study was to tabulate current clinical information from a nationwide survey, to examine two breeds of horses, one of which has a greater incidence of laminitis, and to investigate metabolic parameters which may relate to increased susceptibility.

The incidence, etiology, and breed susceptibility to laminitis, as well as therapies and rates of success in treating the condition, were assessed through a nationwide poll of 235 equine practitioners. Laminitis was shown to occur in 0.92% of the horse population with the Quarter Horse being the most susceptible breed. The principal causative agents reported were overeating and obesity. In practices limited to either Quarter Horses or Thoroughbreds (the two most common breeds in the United States), the Quarter Horse was found to have an incidence of laminitis eight times greater than the Thoroughbred, and the recovery rate of the Quarter Horse is 1.3 times higher. Thoroughbreds, however, showed a fivefold higher death rate primarily due to complications of the disease. Most practitioners expressed frustration with the current treatments available, and although certain therapies such as antibiotics and forced exercise appear to be used almost exclusively by practitioners having higher recovery rates, therapeutic measures among most practitioners are haphazard and often without any scientific rationale.

It is proposed that perhaps different forms of the disease exist and are caused by different factors which may be breed specific. Therefore, treatment of laminitis may have to be tailored to the specific type of this disease exhibited by an animal.

Concentrations of serum phospholipids, triglycerides, total cholesterol, non-esterified fatty acids, and glucose were determined for 9 months (September 1972 to May 1973) in 15 fasting horses (8 Morgans and 7 Thoroughbreds).

Morgan horses had higher concentrations of total lipid than did Thoroughbreds, although the relative proportions of each type of lipid were similar in the two breeds. In both breeds of horses, concentrations of serum triglycerides in the cold months (December to March) were lower than those in the warm months. The significance of these findings is discussed.

Glucose, epinephrine and insulin tolerance tests, as well as glucagon and propionate responses, bromsulfphthalein clearance, and thyroid function tests, were utilized to measure differences between Morgan and Thoroughbred horses in metabolic patterns associated with susceptibility to laminitis and fatty liver.

The Morgan horse showed lesser ability to clear and metabolize glucose in response to glucose, insulin and epinephrine administration. The amount of insulin secreted by the Morgan was also less than in the Thoroughbred, and the Thoroughbred horse was shown to be more prone to hypoglycemic shock. Increased mobilization and clearance of non-esterified fatty acids during epinephrine administration and insulin tolerance tests were seen in the Morgan but not in the Thoroughbred, possibly indicating a difference in the primary energy source between the two breeds. Volatile fatty acids do not appear to contribute significantly to the overall energy metabolism of the short-term fasted equine. Thyroid tests showed the Morgan to tend toward hypothyroidism, and bromsulfphthalein clearance after a glucose load indicated some degree of hepatic impairment. The Morgan horse appears metabolically predisposed to, and therefore more susceptible to, laminitis and the associated fatty liver than the Thoroughbred.

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