Background: Fibrosis of adipose tissue and adipocyte hypertrophy are key histopathologic features of obesity in human metabolic syndrome. Multiple tools have been validated in human medicine to assess these changes. Characterization of obesity-associated structural changes in equine adipose tissue is limited, particularly in the metabolically active nuchal ligament deposit.Hypothesis/
Objectives: To assess the utility and repeatability of a validated human adipose fibrosis scoring system (FAT) and automated adipocyte measurement software (Adiposoft) for evaluation of equine nuchal ligament adipose tissue. Both degree of fibrosis and adipocyte size are expected to be greater in obese vs lean horses.Animals: Ten university-owned mares.
Methods: Nuchal ligament adipose punch biopsies were obtained and assigned equine fibrosis of adipose tissue (eFAT) scores based on the established human scoring system. Adipocyte diameter was measured manually and using Adiposoft with and without manual corrections; these were compared using a Kruskal-Wallis test. Spearman correlations were used to assess relationships between adipocyte diameter, eFAT scores, and multiple metrics per horse.
Results: Adipocyte diameter was significantly correlated with recent weight gain (p=0.02) with no other significant correlations. Mean adipocyte area was significantly greater when measured manually than by Adiposoft (p=0.003) due to numerous errors in the program's recognition of adipocytes in the presence of fibrosis. Fibrotic changes in equine adipose tissue mirrored those seen in humans but interobserver agreement utilizing eFAT scoring was variable.Conclusions and Clinical Importance: Equine adipocyte hypertrophy was associated with recent weight gain. Adiposoft and eFAT scores require refinement before use in fibrotic equine adipose tissue.
