A ten year-old mare, 320 kg, was referred with signs of lameness and reluctance to ambulate. On clinical examination, animal showed signs of shifting weight lameness on the forelimbs, presence of palpable supracoronary depressions and severe signs of pain with hoof test pressure over the sole on right forelimb. Digital pulses and temperature of the hoof were thought to be within normal limits. On inspection it was possible to observe a short extension of the toe and solar prolapse with hoof capsule distortion. Radiologic measurements showed displacement of the distal phalanx (30o). The animal was diagnosed with Obel grade IV chronic laminitis on the right foot. Therapeutic protocol established included exclusively corrective trimming and intramuscular, peritendinous and intrarectal administration of oxygen/ozone therapy as anti-inflammatory therapy. Oxygen/ozone therapy sessions were performed twice a week, for a total of 20 sessions. Six months after original presentation, the mare demonstrated clinical improvement with an improved body condition and better ambulation. Radiologic evaluation showed a normal relationship between the dorsal hoof wall and the distal phalanx.