Cardiovascular, acid-base, electrolyte, and plasma volume changes in ponies developing alimentary laminitis.

The research article discusses the effects of a high-starch diet on Shetland ponies, observing that a certain percentage of those fed in such a way developed a condition called laminitis. The study also looked at the potential symptoms and indicators of laminitis, as well as the general physiological changes that occurred.

Experimental design and subject selection

• For the purposes of their study, the researchers chose twelve Shetland ponies. These ponies were then fed a high-starch ration to observe the physiological changes that might occur.

Observations and findings

• The research found that seven of these twelve ponies developed transient metabolic acidosis and subsequently laminitis approximately 56 hours after overfeeding. Metabolic acidosis describes a condition in which the body’s pH level begins to acidify beyond acceptable levels, indicating a disturbance in the natural biochemical balance.
• These seven ponies also presented with persistent hypokalemia (low potassium levels), hyperthermia (high body temperature) and an increased heart rate. All of these symptoms manifested 24 hours prior to the onset of lameness, a key indicator of laminitis.
• However, other physiological parameters such as serum sodium, serum chloride, hematocrit, plasma volume and blood volume remained unchanged.
• When clinical signs of laminitis began, the ponies had an increase in cardiac output and blood pressure, although overall peripheral resistance was unaffected.

Implications and unresolved questions

• Despite the observational data yielded during the study, none of the measured or estimated values was found to be predictive of laminitis onset. This implies the condition still can’t be diagnosed prior to its onset with full certainty.
• The researchers noted that hypertension was, in fact, a response to lameness rather than a cause of it. This contradicts assumptions of a direct causative relationship between increased blood pressure and laminitis.
• Of the remaining ponies, three died, apparently from shock approximately 29.3 hours after overfeeding. All three were noted to have severe metabolic acidosis, decreased cardiac output, systemic arterial pressure drop, plasma volume reduction and heighten hematocrit, total peripheral and pulmonary vascular resistance levels.
• The last two ponies were either unaffected or euthanized, though the reason for the latter was unspecified.