# Research Progress in the Early Warning of Chicken Diseases by Monitoring Clinical Symptoms
###### Abstract
Biochemical testing is sensitive, and its results usually are reliable, but it usually involves complex sample pretreatment steps and requires professionals to operate, so it is not conducted in real time and usually expensive. Manual inspection is time consuming, labor intensive and may produce inaccurate results. Traditional poultry disease surveillance methods may miss the best time for disease warning, especially for some severe infectious diseases, which can no longer meet the needs of the rapidly developing poultry industry. Sick poultry can be identified from multiple aspects, such as vocalization, body temperature, feces and daily behaviors, which may have corresponding abnormal changes. Therefore, the health state of poultry can be evaluated from these clinical symptoms. Figure 1 shows the route of infection and possible clinical symptoms of poultry diseases. Figure 1: The route of infection and possible clinical symptoms of poultry diseases. Disease infection in poultry can be divided into endogenous and exogenous infection according to the pathogen source. Poultry diseases may cause clinical physiological and behavioral changes and these diseases may be transmitted horizontally or vertically in the flock. Some existing reviews have summarized and analyzed the related studies on livestock and poultry welfare indicators monitoring and pathogen diagnosis from the technical perspective [19; 20; 21; 22; 23; 24]. This review focuses on the clinical symptoms that can be used for early warning and detection of chicken diseases and tries to expound on these symptoms in detail via two dimensions: (1) early disease detection through physiological characteristics, and (2) early disease detection through behavioral characteristics. To detect these characteristics, some monitoring devices will be used, such as microphones and cameras to determine vocalizations; temperature sensors and infrared thermal imagers to determine birds' temperature; acceleration sensors and cameras to note birds' activity; and digital cameras to determine the posture and feces of the birds. Figure 2 shows some commonly used state-of-the-art devices that can be used to detect clinical warnings of poultry diseases. The references used in this review were retrieved from the Web of Science databases. A combination of the following terms was used for reference retrieval: \"Poultry/Chicken/Laying hens/Broiler\", \"Health status\", \"Disease\", \"Vocalization/Sound/Audio/Acoustic\", \"Temperature\", \"Feces/Manure/Excerment\", \"Behavior/Activity/Posture\", \"Warning/Detection/Monitoring/Diagnosis\", \"Machine learning\", \"Deep learning\" and synonyms of the above terms (Supplementary Materials Figure S1). The references were included by the following criteria: (1) The study monitored at least one behavioral or physiological indicator that could be used to reflect chicken health status with a non-invasive intelligent method. (2) The method used in the study is introduced in detail. (3) The study focuses on real-time monitoring on site, and there is no need for human intervention in the monitoring process. This review hopes to achieve the following objectives through detailed analysis of the included references: (1) Provide a basis for the large-scale application of related methods in the future by analyzing the advantages and disadvantages of intelligent monitoring methods. (2) Summarize the clinical symptoms of some common poultry diseases and propose potential clinical symptoms that may be used for disease warning. (3) Put forward the prospect for the future research of poultry disease early warning and detection. In this way, we are looking forward to making a significant contribution to the poultry industry. Figure 2: Some commonly used state-of-the-art devices, including microphones, sensors and cameras, can be used to obtain physiological and behavioral information of poultry to detect clinical warnings of poultry diseases.