Key points and common diseases of ventilation management at different time periods in autumn and winter

In autumn and winter, daytime temperatures can reach approximately 25°C, while nighttime temperatures may drop to around 10°C or lower. This significant diurnal temperature fluctuation poses considerable challenges for poultry house management. During the day, as temperatures rise, ventilation systems must be adjusted toward summer-mode operation; conversely, as temperatures decline at night, a transition to minimum ventilation mode becomes necessary. Ventilation strategies during these seasons can be summarized as follows: "Manage the day like summer, and the night like winter." The key considerations are when and how to switch between these two operational modes. The following outlines the primary time periods and corresponding management practices.

Heating Period (7:00–12:00)  
(1) From 7:00 to 9:00, external temperatures remain relatively stable. However, decreasing humidity leads to a lower perceived temperature. To prevent excessive ventilation stress on the flock, fans should be operated intermittently with extended runtime rather than continuous operation.  
(2) Between 9:00 and 13:00, ambient temperatures rise rapidly and humidity decreases, leading to increased internal shed temperatures. Ventilation should be controlled based on time intervals, with gradual increases in fan runtime and adjustments to inlet opening area to regulate airflow volume.

High-Temperature Period (13:00–16:00)  
This period typically experiences the highest daily temperatures. The primary objective of ventilation is cooling. Airflow volume and wind speed within the house should be increased accordingly. When indoor temperature exceeds the target by 6°C, evaporative cooling via wet pads may be initiated to enable mixed ventilation. If the temperature surpasses the target by 8°C, side wall openings should be closed, directing all incoming air through the wet pads. Care should be taken to avoid excessively high negative pressure.

Cooling Period (16:00–24:00)  
This phase represents a rapid cooling stage. Although outdoor temperatures decrease significantly and humidity remains low, it is essential to calculate the effective temperature (thermal comfort level) and proactively reduce fan usage. Once the target temperature is reached, the system should transition to minimum ventilation mode to maintain thermal stability.

Low-Temperature Period (01:00–06:00)  
During the latter part of the night, humidity levels begin to rise. Therefore, fan runtime under time-controlled ventilation should be slightly extended compared to the earlier night hours. This period is generally thermally stable, with ventilation focused on maintaining air quality. Attention should also be paid to prevailing wind directions, particularly northerly winds in the early morning.

Recent field visits to several poultry farms have revealed a common issue: birds over 20 days of age exhibiting persistent respiratory symptoms that are difficult to treat. In cases where feed intake has not declined significantly, mortality remains low. However, upon administration of medication, clinical signs tend to improve temporarily.

Around day 35, affected flocks often show progressive deterioration, characterized by increasing respiratory distress, abnormal vocalizations, open-mouth breathing, elevated mortality, reduced feed consumption, and diarrhea.

The author categorizes this clinical presentation as secondary bacterial infection following mild avian influenza and mycoplasma infection—commonly referred to as mixed infection. In some cases, post-mortem findings include hepatic congestion, liver discoloration, renal swelling, hemorrhage, and tissue necrosis.

What might be the underlying causes?  
It is widely recognized that Newcastle disease virus and avian influenza viruses are prevalent across commercial and backyard poultry operations. The onset of disease depends on multiple factors, including flock immunity levels, housing conditions, management practices, and the effectiveness of vaccination and biosecurity protocols. Any deficiency in these areas creates an opportunity for pathogen invasion, sometimes resulting in unexpected outbreaks.

This situation demands serious attention.  
In northern regions during late autumn, morning temperatures hover around 10°C, rising to nearly 20°C at noon. After sunset, temperatures quickly fall below 10°C, and nighttime conditions can become extremely cold. Many flocks develop so-called "cold draft" illnesses during the night—particularly between 1:00 and 2:00 a.m.—when temperatures reach their lowest and atmospheric pressure drops. At this time, farmer vigilance is typically reduced, creating favorable conditions for viral proliferation.

The author recommends maintaining nighttime temperatures 1–2°C higher than daytime setpoints, and further increasing the target by 1–2°C on cloudy or windy days compared to clear, calm conditions. Broilers are highly sensitive to environmental changes; raising them requires care comparable to tending children under three years old. Their immune systems are inherently weak—so fragile that they cannot tolerate even minor stressors. Those who choose broiler farming must be prepared for such demanding responsibilities.

Drawing a parallel with human influenza, consider how young children respond to fever: they may respond well to antipyretics during the day, only to experience recurrent high fever at night. Why does this occur?  
Because the body continues to combat an ongoing viral infection and inflammatory response. Effective treatment should therefore address fever reduction, inflammation control, and antiviral support. However, viruses do not respond predictably—even intravenous therapy may fail to eliminate them. (This analogy refers to pediatric care.) But what about chickens? Intravenous treatment is not feasible. What then should be done?

A comprehensive pharmacological approach is required. The recommended strategy involves combining traditional Chinese medicine and Western pharmaceuticals for fever reduction and antiviral effects, along with Western anti-inflammatory agents. It is crucial to select the most effective available medications. Prioritizing cost savings over efficacy may result in suboptimal outcomes and delay critical intervention. Anti-inflammatory drugs should specifically target bacteria commonly associated with respiratory infections. Failure to control respiratory disease at this stage may lead to severe pulmonary and tracheal obstruction, causing mortality rates to increase sharply—sometimes beyond control even with injectable treatments.