I. Causes of respiratory symptoms
1, large temperature differences and cold stress
Sudden cold stress often reduces blood flow to the tracheal mucosa and skin through the body's neuroendocrine regulation, reducing the number of immune cells distributed in these areas. The clearance of foreign matter by the cilia-mucus transport system of the tracheal ciliated epithelium declines, making it easier for pathogens to remain in and infect the respiratory system.
Cold is a key trigger for respiratory diseases. Cold stimuli cause peripheral blood vessels to constrict and reflexively cause blood vessels in the body's deeper tissues and viscera to dilate and become congested. Prolonged passive congestive stasis creates favorable conditions for pathogen transmission. The respiratory mucosal barrier is impaired, ciliated epithelial activity stops, lysozyme secretion decreases, tissue protein breakdown intensifies, macromolecular colloidal proteins in the blood increase, and the activity of the reticuloendothelial system weakens, reducing the body's disease resistance. Therefore, preventing cold stress and strengthening the body's ability to withstand it are key to preventing respiratory diseases.
2, poor ventilation
In autumn and winter, farms generally tend to reduce ventilation in poultry houses at night to raise the indoor temperature. However, if this is not adjusted properly, it can easily lead to a stuffy-house situation. When temperatures rise noticeably during the day, ventilation is increased again, causing large fluctuations in the temperature perceived by the flock and resulting in cold-like respiratory symptoms.
When ventilation is inadequate, bacterial pathogens, harmful gases, and dust in the chicken house cannot be effectively removed by airflow. They then remain in the house for long periods. This environment provides bacteria and viruses with a breeding ground, and even a setting for mutation, posing the greatest threat to flock health.
3, low air humidity
Cold, dry air can easily damage the respiratory mucosa, leading to a higher incidence of respiratory disease. This is especially true when the chicken house is dry and dusty, with down, skin flakes, and pathogens airborne. These irritate the respiratory mucosa, stimulating mucus secretion and causing the flock to cough and sneeze.
4, stress from vaccination and cage separation. Broiler farms generally administer a spray vaccine with a live Newcastle disease vaccine at 1 days of age, followed by eye-drop administration of a live vaccine and injection of an oil-emulsion vaccine at 7 days of age. The stimulation and stress response caused by vaccination often results in respiratory symptoms. In addition, during cage separation, if density and temperature differences, including differences between cage tiers, are not managed according to the flock's condition, the flock's perceived temperature may drop, causing excessive stress and respiratory problems.
5, immunosuppressive diseases and mycoplasma transmission and infection
Recently, there have been many immunosuppressive diseases transmitted vertically, especially viral proventriculitis. Although these chickens have also been vaccinated against Newcastle disease, problems with the development of their own immune systems make it difficult for their antibody levels to rise to an effective level of protection.
Mycoplasma infection can be transmitted vertically. The nature of mycoplasma means that flocks infected with field strains are difficult to clear, so vertical transmission is inevitable; only its extent varies. Forced molting leads to cumulative infection risk and declining protective antibody levels. Problems are more pronounced in flocks with vertically transmitted immunosuppressive diseases, resulting in immunosuppression, low disease resistance, severe secondary infections, increased flock mortality and culling rates, reduced egg production and hatchability in breeding chickens, and an increased feed-to-meat ratio in broilers. Disease is more likely to occur in autumn and winter, causing respiratory disease in chickens, with secondary Escherichia coli airsacculitis, H9, and so on. Therefore, it is important to control mycoplasma, protect the integrity of the respiratory mucosal barrier, and enhance the body's disease resistance.
6, physiological function issues
During the embryonic period, the turnover of intestinal mucosal epithelial cells takes about 5 to 11 days. The nutrients required for the development and function of mucosal epithelial cells are mainly supplied through enteral nutrition. Therefore, flocks with poorly developed proventriculi are at their most vulnerable at around a dozen days of age. Meanwhile, the development of submucosal lymphoid tissue may also be affected, making the body highly susceptible to pathogen attack and invasion.
In addition, after about ten-odd days, most maternal antibodies in the chicks have waned to below protective levels. Pathogens can therefore easily breach the body's immune barrier and cause infection during this period.
II. Clinical Solutions
1, Maintain good ventilation
First, improve management by focusing on ventilation and humidity to control relative temperature differences. The target poultry house should be well ventilated without being cold. Manage the perceived-temperature curve and ventilation properly. Pay particular attention to the perceived temperature and oxygen content at 1/2 and 2/3 in the poultry house at night.
Strengthen feeding and management, and maintain appropriate temperature and humidity for each age (especially humidity during brooding). Reduce dust, bacteria, and microorganisms in the poultry house; provide scientific and appropriate ventilation to ensure adequate oxygen levels. Avoid being either overly cautious or reckless. Adjust temperature flexibly by observing the birds, while minimizing temperature fluctuations to prevent significant cold or heat stress. Prevent cold drafts from blowing directly onto the birds. Pay particular attention to the flock’s thermal comfort, and reduce or avoid stress caused by human handling.
2, diseases transmitted vertically and physiological function issues
Scientific and rational selection of a targeted early-treatment plan is essential. During the first ten-plus days, in addition to using starter medication to prevent and control bacterial diseases that can be transmitted vertically, it is more important to promote immune system development, improve glandular stomach function, and compensate for developmental deficiencies. It is also necessary to promptly provide enteral nutrition to flocks whose glandular stomachs have congenital developmental problems, so as to minimize the impact on the early development of the gastrointestinal tract and digestive organs. Therefore, this is the best period for using immune-enhancing and glandular/proventricular gastritis medications. It is also an effective measure for improving the overall condition of the chicks and protecting them from the first wave of infection by external pathogens.
3, strengthen immunization and disease prevention, and biosecurity measures
Based on the prevalent diseases and disease history in the area where the chicken farm is located, reasonably select vaccines and a vaccination program, such as administering the Newcastle disease-infectious bronchitis-avian influenza oil-emulsion vaccine at 1 days of age and 7 days of age, together with eye-drop administration of the Newcastle disease-infectious bronchitis freeze-dried vaccine. Implement biosecurity measures to effectively reduce the spread of infections caused by external pathogens.
4, reasonably select drugs for prevention and treatment
Only by identifying the cause, confirming the diagnosis, and using medication appropriately can ideal treatment results be achieved. For example, some managers may not distinguish conditions well or recognize the right time to administer medication, leading to the wrong treatment approach. As a result, the condition may worsen with treatment, causing unnecessary losses.