Spirulina supplementation regulates inflammation and supports cartilage health in adult sedentary horses following moderate-intensity exercise

Background Horses experience rapid physiological, inflammatory, and oxidative responses during exercise. Spirulina, a nutrient-dense microalga with antioxidant and anti-inflammatory properties, may help modulate these responses and support recovery. Objectives This study evaluated the effects of 30-day dietary Spirulina supplementation on physiological, inflammatory, and oxidative stress responses to moderate-intensity exercise in sedentary horses. We hypothesized that 30-day Spirulina supplementation would modulate hematologic and inflammatory responses and support recovery from moderate-intensity exercise in sedentary horses. Methods Sixteen healthy, sedentary horses (11.4 ± 1.5 years; 528 ± 16 kg) were randomly assigned to Spirulina (SP, 30 g/d; n = 8) or control (C; n = 8) for 30 days. All horses completed a 30-min standardized treadmill exercise test (SET) on day 0 (pre-supplementation) and day 30 (post-supplementation). Jugular blood was collected at baseline, and 10 min, 1 h, 8 h, and 24 h post-SET; synovial fluid was collected from the intercarpal joint at baseline, and 8 h, 24 h, and 120 h post-SET. Samples were analyzed for CBC, biochemistry, nitric oxide (NO), resolvin D1 (RvD1), glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), glycosaminoglycans (GAG), and chondroitin sulfate epitope 846 (CS846). Two-way ANOVA assessed treatment × time within each day, and day × time within each treatment. Results On day 0, groups did not differ. On day 30, SP horses had higher RBC and hemoglobin (p = 0.02, 0.03) and a greater neutrophil:lymphocyte ratio (p = 0.03). Plasma RvD1 was increased in SP horses at 10 min, 1 h, and 8 h post-SET (p ≤ 0.04) and in synovial fluid at 8–120 h (p ≤ 0.03). Plasma NO was lower in SP at 1 h (p = 0.01), whereas synovial fluid NO was higher at 24 h (p = 0.04). No effects were observed for SOD, GSH-Px, CS846, or GAG. Conclusions Spirulina supplementation was associated with modest changes in selected hematologic and inflammatory markers, particularly RvD1 and NO, but did not influence antioxidant enzymes or cartilage biomarkers. These findings indicate limited effects under moderate exercise conditions in sedentary horses.