Determination of reference intervals for symmetric dimethylarginine (SDMA) in Lacaune sheep

Abstract Traditional biomarkers such as serum creatinine and urea often fail to reflect early renal dysfunction, particularly in emaciated animals, as they depend on muscle mass or dietary protein intake. Symmetric dimethylarginine (SDMA), a novel renal biomarker, has shown promise in other species for earlier and more sensitive detection of kidney disease. However, reference intervals for SDMA in ovine species remain undocumented. This study aimed to establish reference intervals for serum SDMA in clinically healthy Lacaune sheep. A reference population of 143 healthy sheep, stratified by age (juvenile < 1 year, adult ≥ 1 year), was selected based on clinical health, body condition score, and serum creatinine concentration. Serum SDMA was quantified using an ELISA validated for cats and dogs. Reference intervals were calculated as 0.59–1.72 µmol/l for all sheep, 0.59–1.56 µmol/l for adults, and 0.59–1.83 µmol/l for juveniles, with juveniles exhibiting significantly higher concentrations ( p < 0.001). No sex-related differences were observed. In a retrospective analysis of 51 deceased sheep with histopathological renal assessments, SDMA concentrations were significantly elevated in animals with severe renal lesions compared to those with no, mild or moderate lesions ( p = 0.005). Creatinine by contrast did not show significant differences. Notably, in animals with poor body condition, SDMA remained effective in identifying individuals with severe renal lesions, whereas creatinine levels remained within or below the reference interval. These findings suggest that SDMA is a more sensitive indicator of renal dysfunction in sheep than creatinine, particularly in emaciated individuals. The established reference intervals provide a foundation for clinical application. The economic feasibility of SDMA testing remains a limitation, but its potential to improve early diagnosis of renal disease in sheep justifies further investigation.