Looking at the level of development in the global layer industry, in terms of disease prevention and control, China faces relatively more issues, particularly for vertically transmitted diseases, when compared to developed countries in Europe and the Americas. As examples, pullorum disease and avian leukaemia have been effectively eliminated in developed countries in Europe and the Americas, and avian Mycoplasma has been eliminated in a number of countries. Therefore, overall speaking, drug use in poultry production in developed countries is much less than in China.
Presently, there are four main categories of diseases affecting layers in China:
The first is new and recurrent infectious diseases. This category of diseases is highly contagious and virulent, and the pathogens responsible are sometimes unknown, making disease prevention and control through vaccination impossible. For example, in the case of fatty liver haemorrhagic syndrome, there is a need for prompt culling and strict biosecurity, and an "early, quick, strict and contained" approach is suggested. 'Early', means strictly implementing a disease reporting system, allowing for the early detection and reporting of the epidemic situation, and enabling relevant authorities to timely grasp the disease progress and carry out appropriate slaughter protocol. 'Quick', means rapidly taking a variety of measures to prevent epidemic spread. 'Strict', means strictly implementing a variety of measures at the epidemic site to eliminate the disease within a defined time period. 'Contained', means controlling the epidemic area to the smallest area possible, thus minimising potential losses. Accordingly, in terms of tackling new and recurrent infectious diseases, there is much room for China to improve on. New diseases should be reported in the earliest time possible. Decisive measures should be taken to eliminate the infection source and cut off the mode of transmission. Concurrently, apart from quarantine and isolation measures, the market circulation of relevant animal products should be banned, and vaccines should be used prudently.
The second is vertically transmitted diseases. Bird populations play an important role in vertical disease transmission; there are either no vaccines applicable to this disease category, or available vaccines are often not effective. Diseases under this category include avian leukaemia, pullorum disease, Mycoplasma gallisepticum, and Mycoplasma Synoviae. Disease prevention and control for this category is primarily through ensuring flock biosecurity.
The third is major poultry diseases. This category includes those which have become endemic in China, such as highly pathogenic avian influenza and Newcastle disease. Prevention and control measures include strengthening biosecurity, using vaccines in a scientific manner, and implementing eradication plans with the aim of achieving zero disease incidence even without an immunisation programme in place. That said, vaccination is relatively important to deal with this category of diseases, otherwise disease would continue to recur and grow.
The last category is highly contagious respiratory diseases. Typical characteristics of this category are omnipresence and rapid infection. Examples of diseases under this category are H9N2 subclinical avian influenza and infectious bronchitis. Prevention and control strategies include strengthening biosecurity, and using vaccines in a scientific manner (accordingly reducing vaccination frequency and dosage).
Disease prevention and control is a systematic and scientific endeavour, with every component being a part of a greater whole, be it drug administration or vaccination. Specifically, vaccination should never be used as a first line of defence. A complete disease prevention and control strategy would include: ensuring farm biosecurity; following an outbreak, restricting movements of animals and animal products, culling of infected animals, carrying out quarantine, isolation, disinfection, and prudent vaccination.
With regard to ensuring the immune status of layer flocks, there are four main issues encountered. Firstly, there are at least 10 disease types which require vaccine use. Secondly, there could be multiple vaccine strains for a particular disease. For example, in the case of infectious bronchitis, there are numerous imported vaccine strains which do not match the prevalent local strains. Thirdly, for a particular disease, the vaccination frequency required could be high, such as for Newcastle disease, avian influenza and infectious bronchitis. Layers require at least 10 vaccinations per production cycle, typically 15, sometimes exceeding 20. Such a scenario is unheard of in many other countries, and there is little scientific basis. Lastly, the above mentioned ultimately leads to excessive vaccine use.