An important factor in the production of poultry is the correlation between avian influenza H9 and poultry performance. This correlation can be investigated through the following points:

1. Avian Influenza (AI) H9: H9N2 belongs to the low pathogenic Avian Influenza Viruses (AIVs) and is one of the widely spread viruses in poultry, which can pose a threat to humans by directly infecting or providing internal genes for various zoonotic avian influenza strains). H9N2 AI is endemic in many countries and presents a serious threat to the poultry sector.
2. Effect on Poultry Performance: H9N2 AI can hinder and reduce the growth rates and weight gain of broilers up to 25%; It can lower the Feed Conversion Efficiency of infected birds through altering metabolism; furthermore, H9N2 AI may have a detrimental effect on layers’ ability to produce eggs, which could result in fewer and lower-quality eggs; Despite being low-pathogenic, H9N2 can still result in mortalities particularly in young birds up to 35%.
3. Immune Suppression: H9N2 AI has the ability to suppress immunity, increasing a bird’s susceptibility to various illnesses.  H9N2 virus can cause severe immune suppression and immune organ damage in broiler chickens and lead to significant reduction in the effectiveness of other poultry disease vaccines.
4. Subclinical Infections: H9N2 infections in birds can frequently manifest as subclinical infections, meaning they may not exhibit overt clinical symptoms. Subclinical infections, however, can still have an impact on overall performance.

In conclusion : Regular monitoring and strict biosecurity measures are crucial to prevent H9N2 AI spread. In addition, vaccination against H9N2 is essential to reduce its impact on performance.