Mycoplasma Gallisepticum (MG) & MS in Chickens: CRD & Treatment
Clinical guide to chronic respiratory disease (CRD), Infectious Synovitis, egg-transmission, and tylosin/tiamulin therapies.
Scientific Overview
Avian Mycoplasmosis refers to infections caused by cell-wall-less bacteria of the genus Mycoplasma. The two most economically damaging species in commercial poultry are Mycoplasma gallisepticum (MG), the causative agent of Chronic Respiratory Disease (CRD), and Mycoplasma synoviae (MS), which causes Infectious Synovitis and eggshell apex abnormalities. Both pathogens are transmitted transovarially (egg-transmitted) and horizontally via air droplets.
Mycoplasma Definition: MG vs MS in Poultry
Avian Mycoplasmosis is defined as a chronic bacterial infection of poultry caused by cell-wall-lacking organisms (Mycoplasma gallisepticum or Mycoplasma synoviae) that colonize the mucosal membranes of the respiratory tract and joint synovia.
Lacking a cell wall, Mycoplasmas are naturally resistant to beta-lactam antibiotics (penicillins, cephalosporins) that target bacterial cell walls, requiring macrolide, tetracycline, or pleuromutilin classes for therapeutic control.
Chronic Respiratory Disease (MG) & Airsacculitis
Mycoplasma gallisepticum (MG) causes Chronic Respiratory Disease (CRD). Signs include tracheal rales, coughing, nasal discharge, and foam in the eye corners (conjunctivitis).
Complicated CRD (CCRD): When MG combines with secondary E. coli or IBV, severe airsacculitis, perihepatitis (fibrinous coating over liver), and pericarditis occur, resulting in heavy broiler condemnation at slaughter and high FCR. Calculate FCR impacts with our FCR Calculator.
Infectious Synovitis (MS) & Joint Lesions
Mycoplasma synoviae (MS) targets joint bursae and tendon sheaths. Affected broilers display hock joint swelling, lameness, breast blisters, and severe depression. MS also causes Eggshell Apex Abnormalities (EAA), producing thin, translucent, easily cracked shell tips.
Diagnostics & Veterinary Antibiotic Dosing
Diagnosis relies on Serum Plate Agglutination (SPA), ELISA, or real-time PCR testing.
Antimicrobial Therapy: Effective antibiotics include Tylosin, Tiamulin, Tilmicosin, and Doxycycline administered in drinking water for 3–5 days. Live MG vaccines (F-strain, 6/85, ts-11) are given to layer pullets to prevent egg transmission.
All scientific data, diagnostic criteria, and performance benchmarks presented on this page are derived from published peer-reviewed journals and official veterinary codes:
- Avian Pathology & Diagnostics: World Organisation for Animal Health (WOAH, 2023). Manual of Diagnostic Tests and Vaccines for Terrestrial Animals. Paris, France.
- Poultry Diseases & Histology: Swayne, D.E., et al. (2020). Diseases of Poultry (14th ed.). Wiley-Blackwell / American Association of Avian Pathologists.
- Nutrition & Feed Chemistry: Leeson, S. & Summers, J.D. (2001). Commercial Poultry Nutrition (3rd ed.). University Books, Guelph, Ontario.
- Commercial Breed Standards: Aviagen (2024). Ross 308 & Cobb 500 Broiler Performance Objectives. / Lohmann Breeders (2024). Lohmann Brown Management Guide.