The effect of weightbearing and limb load cycling on equine lamellar perfusion and energy metabolism measured using tissue microdialysis

Reasons for performing studyLamellar perfusion is thought to be affected by weightbearing and limb load cycling; this may be critical in the development of supporting limb laminitis. ObjectivesTo document the effects of unilateral weightbearing and altered limb load cycling on lamellar energy metabolism and perfusion. Study designRandomised, controlled (within subject), experimental trial. MethodsNine Standardbred horses were instrumented with microdialysis probes in the foot lamellar tissue and skin (over the tail base). Urea (20mmol/l) was added to the perfusate. Samples were collected every 15min for a 1h control period, then during periods of unilateral weightbearing (opposite limb held off the ground for 1h); enhanced static limb load cycling (instrumented limb lifted every 10s for 30min); reduced limb load cycling activity (i.v. detomidine sedation) and continuous walking (30min). Dialysate concentrations of glucose, lactate, pyruvate and urea were measured and lactate:glucose (L:G) and lactate:pyruvate (L:P) ratios were calculated. For each intervention, values were compared with baseline using nonparametric statistical testing. ResultsLamellar dialysate glucose increased and L:G decreased significantly during enhanced static limb load cycling. Glucose and pyruvate increased, and L:G, L:P and urea decreased significantly during walking. Simultaneous skin dialysate values did not change significantly. There were no significant dialysate changes during unilateral weightbearing or after detomidine administration, but only the latter resulted in a significant decrease in limb load cycling frequency. ConclusionsIncreases in limb load cycling frequency (particularly walking) caused dialysate changes consistent with increased lamellar perfusion. Unilateral weightbearing (1h) and a sedation-induced reduction in limb load cycling frequency did not have a detectable effect on lamellar perfusion. More research is needed to confirm the role of hypoperfusion in supporting limb laminitis, but strategies to increase limb load cycling may be important for prevention.