The effect of reversible left recurrent laryngeal neuropathy on the metabolic cost of locomotion and peak aerobic power in thoroughbred racehorses.

This research studied the impact of a temporary condition known as left recurrent laryngeal neuropathy (LRLN) on four trained racehorses’ metabolic cost of locomotion and their peak aerobic power. It was observed that inducing LRLN reduced aerobic power at high exercise intensities and slightly affected horses’ performance.

Study Overview

• The research aimed to analyze the influence of a reversible condition called left recurrent laryngeal neuropathy (LRLN) on the metabolic cost of locomotion (how much energy is expended while moving) and peak aerobic power (maximum capacity of the body to transport and utilize oxygen during incremental exercise) in Thoroughbred racehorses.
• The condition was induced by subcutaneous infusion of a local anesthetic, 2% mepivicaine, into the area where the left recurrent laryngeal nerve passes cauda to the cricoid cartilage.
• The study was conducted using a treadmill exercise test (TET), with each horse undergoing the test four times, alternating between periods of normal upper airway function and induced LRLN.
• Various metrics were measured during these tests, including the horses’ oxygen consumption (VO2), carbon dioxide production (VCO2), venous lactate concentrations (LAC), and heart rate (HR).

Observations and Findings

• The research discovered that induced LRLN did not affect the relationship between VO2 and treadmill speed at exercise intensities where VO2 was less than peak oxygen consumption (VO2peak) which is at speeds less than 9 m/sec.
• However, there was a noticeable decrease – totaling 15.3% – in VO2peak at higher treadmill speeds when the horses had induced LRLN. The average VO2peak reduced from 165.3 +/- 3.4 mL/kg/min in normal condition to 140.0 +/- 3.2 mL/kg/min in LRLN condition.
• The lactate peak (LACpeak) remained unaffected after inducing LRLN.
• It was noticed that the relationship between heart rate and treadmill speed increased at exercise intensities where oxygen consumption was less than the peak consumption. Though, peak heart rate (HRpeak) did not change with LRLN.
• The performance of the horses, as indicated by the maximum number of speed intervals completed (STEPmax), decreased by 7% with induced LRLN, implying that their ability to perform was slightly reduced.
• The study also noted that there was no evidence of a training effect where the horses would have learned response that could have caused a decrease in performance, during the course of the experiment.