When chickens suffer from respiratory diseases, in addition to infections caused by various viruses, bacteria, and mycoplasmas, damage to the respiratory system organs can occur, which leads to localized inflammation, such as redness, swelling, bleeding, edema, and mucous exudation. Particularly in the trachea, the presence of thick mucus can easily adhere to the airway walls and cause blockages, especially in narrower areas like the bronchi and bronchioles, leading to symptoms like neck stretching, wheezing, and abnormal calls, all of which are signs of respiratory distress. In cases like these, relying solely on antiviral, antibacterial, and antimycoplasmal drugs often does not provide significant relief because these drugs have difficulty reaching the mucous-filled airways, where bacteria and mycoplasmas may be hiding.

Therefore, when treating respiratory diseases in chickens, it is important to use not only antimicrobial and antiviral drugs but also symptomatic treatments for respiratory diseases.

For example, drugs like Ambroxol Hydrochloride, Bromhexine Hydrochloride, Theophylline, Ammonium Chloride, Potassium Iodide, Acetylcysteine, Dipropylamino-methylxanthine, and other medications for respiratory diseases, such as Ma Xing Shi Gan Oral Liquid, Sang Ren Qing Fei Oral Liquid, and Ding Chuan San, can be used.

Symptomatic drugs for respiratory diseases, such as antitussives, mainly act on the cough center in the medulla oblongata to suppress coughing. These drugs can inhibit the secretion of bronchial glands and the movement of cilia, which can increase the viscosity of mucus, making it harder to expel. This can cause airway blockages and secondary infections, so they should be used cautiously to avoid worsening respiratory difficulties. Expectorants, which are commonly used, include mucolytics that dissolve or thin mucus, making it easier to expel.

1. Nauseant Expectorants
   These drugs, when taken orally, stimulate the gastric mucosa and promote an increase in bronchial gland secretion through vagus nerve reflexes, thereby thinning mucus and making it easier to cough up. They also increase the osmotic pressure in the respiratory tract to retain moisture and dilute the mucus. These drugs are suitable for dry coughs and cases where mucus is difficult to expectorate.

   Ammonium Chloride is a representative of this category. It can cause nausea and vomiting in animals, and excessive or prolonged use may lead to acidosis and hypokalemia. It is also a common component in some traditional Chinese medicine expectorant formulations. However, it should be used with caution in cases of abnormal physiological responses in livestock, as it may cause hypoxia and/or acidosis. This drug is contraindicated in combination with sulfonamides such as sulfadimidine, sulfamethoxypyridazine sodium, and sulfadichlorine sodium.

2. Irritant Expectorants
   These drugs stimulate bronchial secretion, thinning the mucus to make it easier to expectorate.

   Guaifenesin is a representative drug in this category. In addition to its expectorant effect, it also has a mild antibacterial action and reduces the foul odor of mucus. However, it should be used with caution in cases of lung hemorrhage, nephritis, or renal syndrome.

3. Mucolytic Drugs
   These drugs are suitable for treating respiratory distress and difficulty in expectorating due to viscous mucus. They work by breaking the disulfide bonds in mucoproteins, which helps degrade the DNA in mucus, thus reducing the viscosity and making it easier to expel.

   • Acetylcysteine: This drug breaks the disulfide bonds in mucous proteins, reducing the viscosity of the mucus. It is effective for both purulent and non-purulent mucus. It can be administered through nebulization or orally. However, it has a strong odor and can irritate the respiratory tract.

   • Bromhexine: This drug inhibits the synthesis of acidic mucopolysaccharides in the trachea and bronchial glands, while promoting the secretion of small molecular mucoproteins, which reduces the viscosity of mucus and facilitates its expulsion. It also promotes ciliary movement in the respiratory mucosa, helping to expel mucus. It begins to work within one hour of administration, peaks at 3–5 hours, and lasts for 6–8 hours. It is used for conditions like bronchitis, emphysema, and bronchiectasis with white, viscous mucus that is difficult to cough up.

   • Ambroxol: This drug belongs to the category of mucolytics and not only inhibits the synthesis of acidic mucopolysaccharides in the trachea, bronchi, and bronchial glands but also promotes ciliary movement to help expel mucus, thus improving respiratory function. It also increases the surface-active substances in the respiratory mucosa, helping to restore its normal protective function. It reduces the viscosity of mucus, making it easier to expel.

   Ambroxol is a metabolite of Bromhexine, and it has stronger expectorant effects with less toxicity. When used together with antibiotics (such as compound amoxicillin, cefquindox, tilmicosin, or doxycycline), it can increase the concentration of these drugs in the lung tissue.