Metabolic heterogeneity exists across equine distal limb tendons and ligaments in healthy, metabolically normal horses.

Objective: To (1) identify tissue-specific metabolic profiles of the superficial digital flexor tendon (SDFT), deep digital flexor tendon (DDFT), and suspensory ligament (SL) and (2) evaluate metabolic profile differences in the SDFT, DDFT, and SL between the equine forelimb and hindlimb.

Methods: 2 SDFT, DDFT, and SL specimens were collected from the forelimbs and hindlimbs of 10 horses of mixed breed, age, and sex that were euthanized for other reasons. One specimen was processed for histology to confirm that there were no underlying soft-tissue pathologies. One specimen was processed for 2 forms of untargeted metabolomics: (1) gas chromatography-mass spectroscopy for polar metabolites and (2) UPLC-MS for nonpolar metabolites. Comparisons were made between tissue types (SDFT, DDFT, and SL) in the same limb and between limbs (forelimb and hindlimb) for the same tissue.

Results: Metabolic differences, specifically in the taurine and glycerolipid pathways, were evident between the tendons and ligaments. Metabolic differences, including changes in trihexosylceramides and fatty acyls, were also seen when comparing the forelimbs and hindlimbs of the tendons and ligaments, respectively.

Conclusions: The current study has established metabolic differences in tendons and ligaments in a group of metabolically healthy horses.

Clinical relevance: Understanding these metabolic differences may allow for exploration into targeted intervention strategies for these tissues that may prevent injury as well as promote healing and a return to function.