# Research Progress in the Early Warning of Chicken Diseases by Monitoring Clinical Symptoms
###### Abstract  
Global animal protein consumption has been steadily increasing as a result of population growth and the increasing demand for nutritious diets. The poultry industry provides a large portion of meat and eggs for human consumption. The early detection and warning of poultry infectious diseases play a critical role in the poultry breeding and production systems, improving animal welfare and reducing losses. However, inadequate methods for the early detection and prevention of infectious diseases in poultry farms sometimes fail to prevent decreased productivity and even widespread mortality. The health status of poultry is often reflected by its individual physiological, physical and behavioral clinical symptoms, such as higher body temperature resulting from fever, abnormal vocalization caused by respiratory disease and abnormal behaviors due to pathogenic infection. Therefore, the use of technologies for symptom detection can monitor the health status of broilers and laying hens in a continuous, noninvasive and automated way, and potentially assist in the early warning decision-making process. This review summarized recent literature on poultry disease detection and highlighted clinical symptom-monitoring technologies for sick poultry. The review concluded that current technologies are already showing their superiority to manual inspection, but the clinical symptom-based monitoring systems have not been fully utilized for on-farm early detection. clinical symptoms; disease warning; automatic monitoring; physiological characteristics; behavioral characteristics +
Footnote †: journal:shifted from discrete and miniaturized to intensive and large scale in the past few decades. However, in dense environments, the risk of disease transmission would be increased. In order to solve this problem, breeding scientists are committed to cultivating poultry breeds with both high production performance and high disease resistance. However, with the improvement of production performance, some physiological functions such as adaptability and disease resistance of poultry are limited [6]. [PERSON] [7] found that high productivity induced high susceptibility to MD ([PERSON]'s disease) and [PERSON] [8] found that egg production performance was negatively correlated with resistance to MD. Poultry disease, regarded as one of the crucial factors affecting poultry production, has restricted the development of the poultry industry for a long period [6]. Although researchers and breeders have conducted a lot of work in disease prevention and control, such as disease-resistant breeding [6; 9], immune-related products [10; 11] and enhancement of routine measures, the outbreak of poultry diseases is still inevitable, which will not only cause huge economic losses, but some zoonotic infectious diseases may also endanger human life [12; 13; 14]. Since the European Union banned the use of antibiotics as growth promoters in 2006 [15], the poultry industry has entered an era without antibiotics, which may lead to adverse effects on production performance (such as weight gain, feed conversion ratio, mortality rate and yield) [16]. In addition, there was another European Union announcement to phase out and eventually prohibit the use of cage-rearing systems to rear laying hens in all European Union member countries by 2027, which will undoubtedly exacerbate the negative impact of disease on poultry industry. Studies have shown that the mortality of laying hens during the laying period is related to the rearing patterns, with the mortality rate in free-range systems nearly twice that of the cage-rearing systems [17; 18]. Disease surveillance and early warning are necessary to decrease poultry mortality and increase yields. Traditional disease detection methods rely mainly on experienced veterinarians for manual observation or biochemical testing with related instruments [19].