In autumn, the diurnal temperature difference widens, and cold stress occurs frequently. The contradiction between keeping the chicken house warm and ventilating it becomes prominent. The accumulation of ammonia and dust in the house easily damages the respiratory mucosal barrier. At the same time, the risk of virus introduction by migratory birds rises, and environmental pathogens proliferate in large numbers. The immunity of laying hen flocks generally declines. The core high-incidence type of disease is mixed respiratory infection, accompanied by risks of intestinal and parasitic diseases. It can be specifically divided into four major categories:

I. Viral diseases (the most serious hazard, and the source of primary infection)

1. H9 subtype low-pathogenic avian influenza

· Core position: The most frequently occurring viral disease on autumn laying hen farms, and also the initiating factor of most mixed respiratory infections.

· Disease triggers: Virus introduction by migratory birds, and fluctuations in antibody levels caused by cold stress. Outbreaks are likely when vaccine strains do not match circulating strains.

· Typical symptoms: Respiratory symptoms are mild (coughing, nasal snicking, tracheal rales), and there is no obvious effect on spirit or feed intake. It very easily leads to secondary infection by Mycoplasma, E. coli, infectious bronchitis, and other pathogens, forming multiple infections.

· Production harm: Egg production decreases by 10%-30%. Eggshell color fades, and thin-shelled and sand-shelled eggs increase. Fertility and hatchability of breeding eggs decrease. At the same time, it causes severe immunosuppression, and the risk of subsequent diseases in the flock rises greatly.

2. Atypical Newcastle disease

· Disease triggers: Unreasonable immunization procedures and uneven antibody levels. Cold stress induces a rapid decline in antibodies.

· Typical symptoms: Sporadic coughing and nasal snicking appear in the flock, and feces are yellow-green and loose. Generally, there is no large-scale acute death.

· Production harm: Egg production declines slowly. Eggshells become pale, egg weight decreases, and the culling and mortality rate rises slightly.

3. Infectious bronchitis (IB)

· Disease triggers: Large diurnal temperature differences and stress from direct cold wind. The virus can spread rapidly through the air.

· Typical symptoms: The respiratory type manifests as tracheal rales, neck stretching to breathe, and coughing. The reproductive type directly damages the oviduct.

· Production harm: Egg production drops sharply (by 20%-50%). Deformed eggs, soft-shelled eggs, and shell-less eggs increase greatly, and egg white is thin and watery. Infection in chicks causes permanent damage to the oviduct, and they become "false layers" after reaching adulthood.

4. Egg drop syndrome (EDS-76)

· Pathogen: Avian adenovirus, which can be transmitted vertically.

· Disease triggers: In autumn, the antibody levels of flocks that are starting to lay or are at peak production decline naturally, and stress activates the virus.

· Typical symptoms: The flock shows no obvious external abnormalities, and feed intake and spirit are basically normal.

· Production harm: Egg production suddenly drops by 20%-40%. Thin-shelled, soft-shelled, and shell-less eggs increase, and eggshell color generally becomes lighter.

5. Infectious laryngotracheitis

· Disease triggers: A sudden drop in temperature in late autumn and excessive flock density. It spreads extremely quickly.

· Typical symptoms: Severe difficulty breathing, neck stretching and open-mouth breathing, head shaking and coughing up blood, and yellow caseous pseudomembranes in the larynx.

· Production harm: Egg production drops greatly, and the culling and mortality rate rises significantly.

II. Bacterial diseases (mostly secondary infections, worsening the condition)

1. Colibacillosis

· Core characteristics: A typical opportunistic pathogen, and secondary infection occurs after almost all respiratory viral infections.

· Disease triggers: The respiratory mucosal barrier is destroyed by viruses, poor house sanitation, and excessively high ammonia concentration.

· Typical symptoms: Necropsy shows pericarditis, perihepatitis, and airsacculitis. Laying hens frequently develop yolk peritonitis, and pass yellow-green loose feces.

· Production harm: The culling and mortality rate rises, egg production remains persistently low, and oviduct inflammation leads to poor eggshell quality.

2. Infectious coryza

· Pathogen: Avibacterium paragallinarum.

· Disease triggers: Sudden temperature changes, poor ventilation, and crowded flocks.

· Typical symptoms: Serous or purulent nasal discharge, facial edema, eyelid swelling, and frequent sneezing.

· Production harm: Feed intake decreases, and egg production drops by 10%-20%. It spreads quickly and can affect the whole flock in a short time.

3. Fowl cholera (Pasteurella multocida infection)

· Disease triggers: Induced by strong stress such as alternating cold and heat in autumn and transfer between houses. It often occurs as an acute outbreak.

· Typical symptoms: The peracute type causes sudden death without warning. In the acute type, the comb turns purple, the wattles become edematous, gray-green loose feces are passed, and pinpoint gray-white necrotic spots appear on the liver surface.

· Production harm: Acute deaths increase, and egg production drops rapidly.

4. Pullorum disease (Salmonella infection)

· Disease triggers: Vertical transmission through hatching eggs plus environmental contamination. Outbreaks occur when resistance declines due to temperature-difference stress in autumn.

· Typical symptoms: Adult laying hens are mostly subclinically infected, pass white or yellow-green loose feces, and have ovarian deformation and necrosis.

· Production harm: Egg production declines, breeding eggs carry the bacteria, hatchability is low, and chick survival rate is poor.

III. Mycoplasma and respiratory syndrome (the most common disease form in autumn)

Mycoplasma gallisepticum infection (chronic respiratory disease)

· Core characteristics: Commonly present on autumn laying hen farms, with a long course and easy recurrence. It is rarely a single infection.

· Disease triggers: Excessive ammonia in the house, large amounts of dust, and large diurnal temperature differences continuously damage the respiratory mucosa.

· Typical symptoms: Coughing, nasal snicking, and tracheal rales, with symptoms especially obvious at night. There are bubbles in the eyes, and the eyelids are mildly swollen.

· Production harm: When infected alone, egg production declines slightly. When co-infected with infectious bronchitis, avian influenza, E. coli, and other pathogens (commonly known as "respiratory syndrome"), egg production drops greatly, the culling and mortality rate rises significantly, and treatment costs are extremely high.

IV. Parasitic diseases

1. Coccidiosis

· Disease triggers: Rainy autumn weather and high humidity in the house. Feed and drinking water are contaminated by feces. It occurs at high incidence in floor-reared laying hens.

· Typical symptoms: Cecal coccidiosis causes bright red bloody feces, and small intestinal coccidiosis causes brown loose feces. The flock becomes anemic and emaciated.

· Production harm: Feed intake decreases, egg production declines, eggshell color becomes lighter, and mass death can occur in severe cases.

2. Ascariasis in chickens

· Disease triggers: Autumn temperatures are suitable for egg development. Farms with poor environmental sanitation and untimely manure removal are prone to it.

· Typical symptoms: The flock becomes emaciated and has indigestion. Worms can be seen in the feces, and the intestinal mucosa is continuously damaged.

· Production harm: Feed conversion rate decreases, egg production decreases, and egg weight tends to be lighter.