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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.

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Mycoplasma Gallisepticum (MG) & MS in Chickens: CRD & Treatment — Frequently Asked Questions

What is Mycoplasma in chickens? expand_more
Mycoplasma in chickens refers to chronic bacterial infections caused by Mycoplasma gallisepticum (MG, causing respiratory CRD and airsacculitis) or Mycoplasma synoviae (MS, causing swollen joints and lameness).
What antibiotics treat Mycoplasma in poultry? expand_more
Because Mycoplasmas lack cell walls, penicillins are ineffective. Effective antibiotics include Tylosin, Tiamulin, Doxycycline, and Tilmicosin administered in drinking water.
Is Mycoplasma in chickens egg-transmitted? expand_more
Yes. Mycoplasma is transmitted vertically from infected breeder hens through the egg to day-old chicks, as well as horizontally through air droplets.
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Related Pathologies & Differential Diagnosis

bar_chart View Pathology Infographic →

Differential diagnostic screening: Cross-reference clinical lesions and flock symptoms against these closely associated avian pathologies:

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Scanning transmission electron micrograph of Mycoplasma gallisepticum highlighting the specialized terminal tip cytoadhesin organelle biotech Clinical Pathology
Clinical Pathology: Mycoplasma gallisepticum Ultrastructure Morphology • Photo: USDA Agricultural Research Service (ARS) • Public Domain

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Scientific Literature

  • Avian Mycoplasmosis (Mycoplasma gallisepticum, M. synoviae) (MSD Vet Manual, 2023).
  • Diseases of Poultry, 14th Edition (David E. Swayne et al., 2020).
  • WOAH Terrestrial Manual: Avian Mycoplasmosis Standard Diagnostics.