Unusual history and initial clinical signs of Mycoplasma bovis mastitis and arthritis in first-lactation cows in a closed commercial dairy herd.

Case Description: 9 first-lactation dairy cows in a closed dairy herd had swelling in the forelimbs and forelimb lameness. Mycoplasmal arthritis and mastitis were diagnosed.

Clinical Findings: Swelling of the carpal joint, diffuse subcutaneous edema from the carpal to metacarpophalangeal joints, and forelimb lameness were evident in 9 first-lactation cows 7 to 21 days after parturition.