What are the prevention and control measures for common respiratory diseases in chickens?

In recent years, the scale of the breeding industry has continued to expand, showing a trend toward large-scale and intensive development. This large-scale breeding model has likewise made the pressure of preventing and controlling epidemic chicken diseases increasingly greater, among which chicken respiratory diseases are the most serious. Because the symptoms of chicken respiratory diseases are similar and most are mixed infections, prevention and treatment are difficult, and once an outbreak occurs it will bring huge economic losses to farmers. For this reason, Qinnong Network focuses on introducing several common chicken respiratory diseases and their corresponding prevention and control measures, which farmers may find worth a look.

Common chicken respiratory diseases mainly include Newcastle disease, infectious bronchitis, infectious laryngotracheitis, etc. The specific symptoms and prevention and control are as follows:

I. Newcastle disease

1. Overview of disease symptoms

Newcastle disease, also known as Asian fowl plague or fowl plague, is a highly contagious and virulent infectious disease of poultry caused by avian paramyxovirus type I (Newcastle disease virus). It can infect chickens of all ages, and non-immune susceptible flocks will have extremely high morbidity and mortality. The clinical symptoms mainly manifest as elevated body temperature, decreased appetite, yellow-green watery droppings, depression, and varying degrees of respiratory symptoms (coughing, snoring, open-mouth gasping, rales in breathing, etc.). Laying hens will show a decline in egg production and lay white-shelled eggs and deformed eggs. In the later stage of the disease, various neurological symptoms may appear (head twisting, wing paralysis, etc.). Typical necropsy lesions are mainly located at the near-end of the duodenum, 2-3 cm after the yolk remnant of the jejunum, and the beginning of the ileum, where local mucosal congestion and swelling or purple-red date-pit-shaped ulcer foci are commonly seen. The tonsils are swollen and hemorrhagic, and the proventricular papillae are hemorrhagic. In laying hens, ovarian follicles may be congested, hemorrhagic, deformed, or liquefied. The trachea is hemorrhagic, with mucus.

2. Prevention and control measures

The main method of preventing and treating this disease is vaccine immunization. The vaccines commonly used in China include chicken Newcastle disease strain I and strain IV live vaccines and oil-emulsion inactivated vaccines.

Strain I vaccine is a medium-virulence vaccine, used for chickens that have received two doses of attenuated vaccine immunization or are over 2 months of age, by intramuscular injection. It has a certain pathogenicity for chicks. Immunity is produced 3-4 d after vaccination, and the immune period is one year. Chickens vaccinated with this vaccine may experience a certain immune reaction.

Strain IV vaccine is a low-virulence vaccine. The LaSota strain and its cloned strains (such as C30) are used in clinical practice. It can be used for both large and small chickens, and is mostly administered by intranasal drops, eye drops, drinking water, aerosol, and other methods.

Oil-emulsion inactivated vaccine is safe for chickens, can produce lasting immunity, and will not spread the pathogen through the vaccine, but immunity is only produced 10-20 d after injection. Chicken farms should formulate immunization programs and immunization routes suitable for their own farms according to actual conditions, and establish a regular immunization testing system. Affected chicken farms should promptly confirm the diagnosis and carry out emergency immunization. Antiviral traditional Chinese medicine preparations and antibiotics can be used in drinking water for treatment, and effective disinfection methods can be used to kill Newcastle disease virus in the environment.

II. Infectious bronchitis

1. Disease symptoms and overview

Infectious bronchitis is an acute, highly contagious infectious disease caused by infectious bronchitis virus. Chickens are the only natural host of this disease. Chickens of all ages are susceptible, but the disease is most serious in chicks. Chicks within 30 days of age are especially more susceptible. Chickens over 6 weeks of age usually do not die, and laying hens show a decline in egg production and eggshell quality. The main types of infectious bronchitis are the respiratory type, kidney type, proventriculus type, and oviduct type.

The respiratory type mainly affects chickens within 2 weeks of age, commonly causing sinus swelling, nasal discharge, tearing, head shaking, etc. It was the main epidemic type in the early period and causes a serious decline in egg production in infected chickens. Necropsy shows serous, catarrhal, and yellow caseous exudate in the respiratory tract (trachea, nasal passages, and sinus cavities). Caseous exudate can be seen in the trachea of dead chicks.

The kidney type is mostly seen in chicks 20-50 days of age. Mild respiratory symptoms appear in the initial stage, such as rales, sneezing, coughing, etc., but they are only relatively obvious when it is quiet at night. After lasting 1-4 days, the respiratory symptoms disappear, and the flock suddenly develops the disease in large numbers, gradually worsening over 2-3 days, showing anorexia, thirst, listlessness, hunched backs and huddling, and passing watery white droppings containing large amounts of urate. The feathers around the vent are soiled. Sick chickens lose weight due to dehydration, and the pectoral muscles become cyanotic. In severe cases, the skin color of the face and whole body becomes dark and dry, and the legs and neck become dry. The peak of death occurs 10-12 days after onset, death stops at 21 days, and the mortality rate is about 30%. Typical necropsy findings: the kidneys are enlarged and pale, showing a mottled kidney appearance.

The proventriculus type shows extreme emaciation, and necropsy shows extreme swelling of the proventriculus, with spherical enlargement.

The oviduct type mainly manifests as a decline in egg production in laying hens and oviduct cysts.

2. Prevention and control measures

Vaccine immunization is a relatively effective prevention and control measure. The vaccines used mainly include attenuated vaccines such as H120 and H52. In actual production, because there are many serotypes of infectious bronchitis, a single vaccine can only produce protection against the same-type strain, and often produces partial protection or no protection against heterologous strains. Therefore, after immunization with H120 and H52, even if antibody levels are very high, immunization failure may still occur due to infection with epidemic strains. Through a series of experimental studies, it is believed that combining attenuated vaccine H120 intranasal drops with polyvalent inactivated vaccine immunization is an effective method for preventing and treating infectious bronchitis. Immunization program: generally, H120 or IV H120 is mostly used at 1 week of age by intranasal drops or drinking water, and breeder farms mostly use imported vaccines of corresponding strains such as Ma5 by intranasal drops for prevention and treatment. A second immunization with H52 is given at 25-30 days of age. A third immunization with H52 or inactivated vaccine is given at 120-140 days of age. It is recommended that epidemic areas of kidney-type infectious bronchitis use infectious bronchitis variant strain 4/91 live vaccine and variant strain oil vaccine for immunization and prevention.

III. Infectious laryngotracheitis

1. Disease symptoms and overview

Infectious laryngotracheitis is an acute respiratory infectious disease caused by infectious laryngotracheitis virus. Chickens of all ages can be infected, and adult chickens are the most characteristic. It occurs frequently in winter and spring, and the disease has high infection and mortality rates. The disease is characterized by difficulty breathing, coughing, and coughing up mucus containing blood, with hemorrhagic-necrotic inflammation of the laryngeal and tracheal mucosa. Clinically, it is mainly divided into the laryngotracheitis type and the conjunctivitis type. Laryngotracheitis type: characterized by sick chickens showing difficulty breathing, raising the head and stretching the neck, and coughing up bloody sputum when coughing and shaking the head. Necropsy lesions are swelling, congestion, hemorrhage, and even necrosis of the laryngeal and tracheal mucosa, and the tracheal cavity is often filled with blood clots, mucus, and pale yellow caseous exudate. Conjunctivitis type: mainly serous conjunctivitis, manifested as conjunctival edema and congestion. Some sick chickens develop edema of the eyelids, especially the lower eyelid. Some develop fibrinous conjunctivitis and corneal ulcers. Sometimes it is a mixed infection with laryngeal and tracheal lesions.

2. Prevention and control measures

Adhering to strict biosecurity and epidemic prevention measures is an effective way to prevent and control the spread of this disease. Since virus-carrying chickens are one of the sources of infection for this disease, susceptible chickens must never come into contact with recovered chickens or chickens of unknown origin. Immunization and prevention: mainly eye drops with attenuated vaccine and cloacal application with virulent vaccine. Treatment: antiviral drugs plus antibiotics such as doxycycline (to prevent secondary infection), while using antiasthmatic drugs to relieve symptoms.

IV. Infectious coryza

1. Disease symptoms and overview

Infectious coryza (IC) is an acute upper respiratory tract disease of chickens caused by Haemophilus paragallinarum, with inflammation of the nasal cavity and sinuses, runny nose, sneezing, facial swelling, and concurrent conjunctivitis as the main clinical symptoms. Chickens of any age are susceptible, but it is generally less serious in young chickens. It is most common in chickens 8-12 weeks of age. It mostly occurs in the cold seasons of autumn and winter. In typical cases, necropsy lesions are serous, mucous, or purulent inflammation of the nasal cavity, paranasal sinuses, and conjunctiva. In longer courses, yellow, viscous purulent secretions or caseous material accumulate in the paranasal sinuses and infraorbital sinuses, and sick chickens show mild respiratory symptoms and constantly shake their heads.

2. Prevention and control measures

First, strengthen feeding management. The chicken house must have good ventilation, the flock should not be overcrowded, and various stresses should be prevented. Second, do a good job of vaccination. The vaccine for this disease is mainly an inactivated vaccine, generally administered at 70 days of age. Third, there is drug treatment. For affected flocks, sulfonamide drugs are the first choice for treating this disease. The effect is remarkable, but it easily recurs, so a course of erythromycin drug treatment can be added immediately afterward.

V. Chronic respiratory disease

1. Disease symptoms and overview

Chronic respiratory disease is a chronic respiratory disease caused by Mycoplasma gallisepticum infection. The main clinical manifestations are chronic respiratory disease characterized by coughing, runny nose, rales in breathing, gasping, sinus swelling, and facial swelling. Although the mortality rate is low, affected chickens grow slowly, egg production declines, and feed conversion is poor. It can occur throughout the year, and occurs frequently in seasons with changeable climate and cold weather. Necropsy symptoms are large amounts of viscous secretions in the nasal cavity, trachea, and bronchi. In the early stage, the air sacs are mildly cloudy, edematous, and opaque; as the course of the disease lengthens, caseous material forms on the air sacs. It often causes mixed infections with viral diseases and other bacterial diseases, such as colibacillosis, avian influenza, Newcastle disease, infectious bronchitis, etc.

2. Prevention and control measures

The prevention and control of chronic respiratory disease is mainly carried out through purifying breeder chickens, reducing stress-inducing factors, vaccination, and drug treatment.

a. Breeder chicken purification

Chronic respiratory disease is mainly transmitted vertically. Once infected, it is very difficult to cure, and the disease can also induce other diseases. Therefore, the focus of prevention and control is the purification of breeder chickens.

b. Eliminating stress-inducing factors

At present, the infection rate of this disease in chicken flocks in China is extremely high. As long as stress-inducing factors exist, the flock will develop the disease. Special attention should be paid to controlling inducing factors such as poor ventilation, foul air, excessively low or fluctuating house temperatures, excessive density, and the occurrence of viral diseases.

c. Vaccination

In China, there are mainly attenuated vaccines and inactivated vaccines. The former is mainly used for commercial chickens and laying hens, and the latter is mainly used for immunization of breeder chickens.

d. Drug treatment

Commonly selected drugs include doxycycline, tylosin, enrofloxacin, etc. However, chicken mycoplasma can infect the air sacs and form caseous material, making it difficult for drugs to reach that site, so the pathogen survives in the body for a long time and is prone to recurrence. Therefore, once the flock develops the disease, it is necessary to persist with long-term medication, rotate drugs, and use combination medication.

The above is Qinnong Network's introduction to the symptoms and prevention and control measures of common chicken respiratory diseases. It can be seen that most respiratory diseases are contagious to a certain degree, so once they occur, the losses caused are enormous. Farmers must strengthen management during the breeding process to prevent the occurrence of such diseases.