In autumn, the day–night temperature difference widens and cold stress occurs frequently. The conflict between maintaining warmth and ensuring ventilation in chicken houses becomes pronounced, and accumulated ammonia and dust can easily damage the respiratory mucosal barrier. At the same time, the risk of pathogens being carried by migratory birds rises, environmental pathogens multiply rapidly, and the overall immunity of layer flocks declines. Mixed respiratory infections are the most common and central disease type, alongside risks of intestinal and parasitic diseases. These can be divided into four main categories:
I. Viral diseases (the most harmful, and the source of primary infection)
1, H9 subtype low-pathogenicity avian influenza
Core significance: the most prevalent viral disease on layer farms in autumn, and the initiating factor in most mixed respiratory infections
Disease triggers: Migratory birds carry the virus, and cold stress causes antibody levels to fluctuate. Outbreaks are likely when the vaccine strain does not match the circulating strain.
Typical symptoms: Mild respiratory symptoms (coughing, head shaking, tracheal rales), with no obvious effects on activity or feed intake; highly susceptible to secondary pathogens such as Mycoplasma, E. coli, and infectious bronchitis virus, resulting in multiple infections.
Production impact: Egg production rate decreases by 10%–30%; eggshell discoloration and increases in thin-shelled and sand-shelled eggs; reduced fertilization and hatchability rates of hatching eggs. It also causes severe immunosuppression, greatly increasing the flock’s subsequent disease risk.
2, triggers of atypical Newcastle disease: An inappropriate vaccination program and uneven antibody levels; cold stress triggers a rapid decline in antibody levels.
Typical symptoms: The flock shows occasional coughing and head shaking; droppings are yellow-green and loose. Generally, there is no large-scale acute mortality.
Production impact: The laying rate declines slowly, eggshells become pale, egg weight decreases, and the mortality and culling rate rises slightly.
3, infectious bronchitis (IB)
Triggers: A large day–night temperature difference and stress from direct exposure to cold drafts; the virus can spread rapidly through the air.
Typical symptoms: The respiratory form presents with tracheal rales, neck stretching while breathing, and coughing; the reproductive form directly damages the oviduct.
Production impacts: The egg-laying rate drops sharply (by as much as 20％￣50％), and misshapen eggs, soft-shelled eggs, and shell-less eggs increase substantially; the egg whites become watery. Infection in chicks causes permanent damage to the oviduct, making them “false hens” as adults.
4, Egg Drop Syndrome (EDS－76)
Pathogen: avian adenovirus; can be transmitted vertically
Disease trigger: The antibody levels of flocks naturally decline when they begin laying in autumn or during peak production, and stress activates the virus
Typical symptoms: The flock shows no obvious external abnormalities; feed intake and general condition are basically normal
Production impact: The laying rate suddenly drops by 20%–40%; thin-shelled, soft-shelled, and shell-less eggs increase, and eggshell color generally becomes lighter.
5, causes of infectious laryngotracheitis outbreaks: a sharp drop in temperature in late autumn and excessive flock density; the disease spreads extremely quickly
Typical symptoms: severe difficulty breathing, breathing with the neck extended and mouth open, shaking the head and coughing up blood; yellow, caseous pseudomembranes in the larynx
Production hazards: egg production rate drops significantly, and mortality and culling rates rise noticeably
II. Bacterial diseases (mostly secondary infections that worsen the condition)
1, Escherichia coli disease
Key feature: A typical opportunistic pathogen; secondary infection occurs after almost all respiratory viral infections.
Onset triggers: damage to the respiratory mucosal barrier by viruses, poor hygiene in the housing, and excessively high ammonia concentration
Typical symptoms: Necropsy may reveal pericarditis, perihepatitis, and airsacculitis. Laying hens commonly develop yolk peritonitis and pass loose yellow-green droppings.
Production impact: increased mortality and culling rate, persistently low egg production rate, and poor eggshell quality caused by inflammation of the oviduct.
2, infectious rhinitis
Pathogen: Haemophilus paragallinarum
Disease triggers: sudden temperature changes, poor ventilation, and overcrowding of the flock
Typical symptoms: serous / purulent discharge from the nasal cavity, facial edema, eyelid swelling, and frequent sneezing
Production hazards: reduced feed intake, egg production rate decreases by 10%–20%; spreads rapidly and can affect the entire flock in a short time.
3, fowl cholera (Pasteurella multocida disease)
Disease triggers: Strong stressors such as alternating hot and cold conditions in autumn and regrouping can trigger outbreaks, which are often acute.
Typical symptoms: The peracute form causes sudden death without warning; the acute form causes a purplish comb and swollen wattles, with gray-green watery droppings and pinpoint gray-white necrotic spots on the liver surface.
Production hazard: increased acute mortality, rapid decline in egg production rate
4. Pullorum disease (salmonellosis)
Causes of disease onset: vertical transmission through hatching eggs + environmental contamination; outbreaks occur in autumn when temperature fluctuations cause stress and weaken the body's resistance.
Typical symptoms: Adult laying hens are often subclinically infected and develop white or yellowish-green loose droppings; the ovaries become deformed and necrotic.
Production hazards: reduced egg production, contaminated hatching eggs, low hatchability, and poor chick survival rate
III. Mycoplasma and respiratory syndrome (the most prevalent form of illness in autumn)
Mycoplasma gallisepticum infection (chronic respiratory disease)
Key characteristics: Common in layer farms in autumn, with a long disease course and frequent relapses; rarely occurs as a standalone disease
Disease triggers: Excessive ammonia levels and high dust levels in the poultry house, as well as large day-night temperature fluctuations, continuously damage the respiratory tract mucosa.
Typical symptoms: coughing, sneezing, tracheal rales; symptoms are especially pronounced at night; bubbles in the eye and mild eyelid swelling
Production impact: When infection occurs alone, egg production decreases slightly; when co-infected with infectious bronchitis, avian influenza, and E. coli (commonly known as “respiratory syndrome”), egg production drops sharply, the mortality and culling rate rises significantly, and treatment costs are extremely high.
IV. Parasitic diseases
1, coccidiosis
Contributing factors: Frequent autumn rains and high humidity inside the poultry house; feed and drinking water contaminated by feces; high incidence among floor-raised laying hens.
Typical symptoms: Cecal coccidiosis causes fresh, bright red bloody droppings; small-intestinal coccidiosis causes loose, brownish droppings; the flock becomes anemic and loses weight.
Production hazards: reduced feed intake, lower egg production rate, lighter eggshell color, and in severe cases, mass mortality
2, chicken roundworm disease
Disease triggers: In autumn, temperatures are suitable for egg development. Poultry farms with poor environmental sanitation and untimely manure removal are prone to outbreaks.
Typical symptoms: the chickens become emaciated and suffer from indigestion; worms may be visible in the feces, and the intestinal mucosa sustains ongoing damage
Production hazards: decreased feed conversion rate, reduced egg production, and lower egg weight