Laminar microvascular flow, measured by means of laser Doppler flowmetry, during the prodromal stages of black walnut-induced laminitis in horses.

The research article explores the changes in laminar microvascular blood flow (LMBF) in healthy horses versus those with black walnut-induced laminitis and examines the effects of glyceryl trinitrate application on such horses suffering from acute laminitis. The results suggest that the LMBF significantly decreases in horses with black walnut-induced laminitis followed by reperfusion prior to onset of clinical symptoms. Glyceryl trinitrate treatment showed no significant effect on LMBF after clinical signs of laminitis had developed.

Study Design and Methods

Laser Doppler flowmetry, a method used to measure blood flow, was deployed to check the LMBF.

• For the experiment, ten adult healthy horses were chosen as subjects.
• Baseline measures of LMBF were first collected, after which the horses were given deionized water through a nasogastric tube. The LMBF was monitored and measured hourly for the next 12 hours.
• After 24 hours, baseline measures were once again collected, and the horses were given black walnut extract.
• Measurements of LMBF were then obtained hourly for the next 12 hours or until the horses developed Obel grade-3 laminitis.
• At this point, five of the horses were treated with phenylbutazone, while the remaining five were treated with both phenylbutazone and glyceryl trinitrate. Their LMBF was measured hourly for an added 12 hours.

Findings

• Results indicated that LMBF significantly decreased 1 and 2 hours after the administration of black walnut extract but went back to near-baseline values for the ensuing 6 hours.
• Eight hours following the extract administration, there was a second notable drop in LMBF, which persisted till the end of the research study.
• Glyceryl trinitrate showed no significant impact on LMBF.
• Clinical signs of laminitis started to appear 8 to 12 hours after administering the extract.

Conclusions

The study suggests that the onset of black walnut-induced laminitis leads to an initial drop in LMBF followed by reperfusion prior to the appearance of clinical signs. Surprisingly, the application of glyceryl trinitrate treatment after the development of clinical laminitis had no significant effect on LMBF. This suggests that glyceryl trinitrate might not be an effective remedy for improving blood flow in horses suffering from this form of laminitis.