Respiratory infections are common in chickens raised for food production. They can be caused by viruses, bacteria, fungi, and parasites. Some of the most common bacterial respiratory infections in chickens include mycoplasmosis, infectious bronchitis, and colibacillosis. Antibiotics are commonly used to treat bacterial respiratory infections in chickens. Choosing the right antibiotic is important for effectively treating the infection. Some factors to consider when selecting an antibiotic include the causative pathogen, antibiotic sensitivity testing, penetrance into respiratory tissues, and prevention of residues.
Common Bacterial Respiratory Infections in Chickens
Mycoplasmosis
Mycoplasmosis is caused by Mycoplasma gallisepticum and Mycoplasma synoviae bacteria. These bacteria infect the upper respiratory tract and air sacs of chickens. Infected chickens develop sinusitis, tracheitis, and airsacculitis. Symptoms include sneezing, nasal discharge, coughing, difficulty breathing, and reduced egg production. Mycoplasmosis is spread through direct contact and aerosol transmission between infected and healthy birds. It is commonly treated with antibiotics such as tylosin, tiamulin, tetracyclines, and fluoroquinolones.
Infectious Bronchitis
Infectious bronchitis is caused by an infectious bronchitis virus (IBV). Secondary bacterial infections often complicate the disease. Infectious bronchitis virus damages the respiratory epithelial lining, predisposing chickens to bacterial infections. The most common secondary invaders include Escherichia coli, Mycoplasma gallisepticum, and Haemophilus paragallinarum. Infected chickens develop respiratory signs like gasping, coughing, sneezing, and rales. Antibiotics can help control secondary bacterial infections.
Colibacillosis
Colibacillosis refers to respiratory infections caused by Escherichia coli bacteria. The disease typically starts as a primary upper respiratory viral infection, which damages the lungs and air sacs. Secondary E. coli bacteria invade and cause airsacculitis, pneumonia, pericarditis, and septicemia. Infected chickens show increased mortality, viscous nasal discharge, swollen sinuses, and labored breathing. Colibacillosis is treated with antibiotics that are effective against E. coli, such as ampicillin, amoxicillin, and cephalosporins.
Choosing an Appropriate Antibiotic
Several factors should be considered when choosing an antibiotic to treat bacterial respiratory infections in chickens:
Causative Pathogen
Identifying the bacteria involved is the first step. Bacterial culture and sensitivity testing will determine the causative bacteria and their susceptibility to different antibiotics. The antibiotic choice should target the specific pathogen involved.
Antibiotic Sensitivity
In vitro antibiotic sensitivity testing helps determine the most appropriate antibiotic. The chosen antibiotic should be one that the bacteria show susceptibility to in lab testing. This improves treatment efficacy.
Penetrance into Respiratory Tissues
The antibiotic must be able to penetrate into the respiratory system to reach infected areas. Antibiotics with good lung tissue penetrance include tetracyclines, macrolides, and fluoroquinolones. Penicillins and cephalosporins have poor penetrance into the avian respiratory tract.
Prevention of Residues
Antibiotic residues in poultry meat and eggs are a human health concern. Antibiotics that are eliminated quickly from the chicken’s body are preferred to minimize residue risks. Tetracyclines, penicillins, and aminoglycosides tend to have longer residue withdrawal periods compared to sulfonamides, macrolides, and fluoroquinolones.
Cost-effectiveness
The antibiotic’s cost is another consideration, as poultry operations work on tight profit margins. Generics and older antibiotics like tetracyclines, penicillins, and erythromycin are typically the most economical choices. Newer antibiotics tend to be more expensive.
Recommended Antibiotics
Here are some antibiotics commonly used for bacterial respiratory infections in chickens:
Tetracyclines
Tetracycline, oxytetracycline, chlortetracycline
– Broad-spectrum antibiotics that inhibit bacterial protein synthesis
– Effective against mycoplasmas, E. coli, pasteurella, and many other bacteria
– Good distribution into respiratory tissues
Macrolides
Erythromycin, tylosin
– Inhibit bacterial protein synthesis
– Good activity against mycoplasmas, E. coli, pasteurella
– Improved lung tissue penetration compared to penicillins
Sulfonamides
Sulfadimethoxine, sulfaquinoxaline
– Inhibit bacterial folate synthesis
– Primarily effective against E. coli
– Low residue risk
Fluoroquinolones
Enrofloxacin, danofloxacin
– Inhibit bacterial DNA replication and transcription
– Broad-spectrum but prone to resistance
– Excellent distribution into respiratory tissues
– More expensive than older antibiotic classes
Antibiotic Class | Examples | Spectrum | Lung Penetrance | Residue Risk |
---|---|---|---|---|
Tetracyclines | Tetracycline, oxytetracycline | Broad | Good | Moderate |
Macrolides | Erythromycin, tylosin | Narrow | Good | Low |
Sulfonamides | Sulfadimethoxine | Narrow | Moderate | Low |
Fluoroquinolones | Enrofloxacin | Broad | Excellent | Low |
Treatment Considerations
When treating chickens with antibiotics:
– Use narrow spectrum antibiotics when the pathogen is known
– Broad spectrum antibiotics can be first line when the cause is unknown
– Bacterial culture and sensitivity informs antibiotic selection
– Consider antibiotic tissue penetration and residue times
– Follow label directions for dosage and duration of treatment
– Isolate and cull birds not responding to treatment
– Improve ventilation and reduce stocking density to decrease disease spread
– Disinfect housing and equipment between flocks
– Vaccinate chickens to reduce respiratory infections
Prevention
Good management practices can help prevent bacterial respiratory infections in chickens:
– Buy chickens from disease-free flocks
– Quarantine and test new birds for pathogens
– Maintain good ventilation, hygiene, and litter quality
– Avoid overcrowding and stress
– Vaccinate against key respiratory pathogens
– Promptly treat any diseased birds
– Follow an all-in, all-out system for each poultry house
– Clean and disinfect poultry houses between flocks
– Prevent contact with wild birds and pests
Conclusion
Bacterial respiratory infections are a significant concern in commercial chicken flocks. Tetracyclines, macrolides, sulfonamides, and fluoroquinolones are common antibiotic options for treating these infections. The ideal antibiotic depends on the causative bacteria, antibiotic sensitivity patterns, ability to penetrate respiratory tissues, and residue risks. Combined with good management and biosecurity practices, appropriate antibiotic therapy helps control respiratory disease and mortality in chickens. Working with a veterinarian to design an effective treatment and prevention plan gives chicken flocks the best chance of staying healthy and productive.