Vocalization characteristics of laying hens under cage and perch systems

Abstract: In order to analyze the effects of different rearing systems and stages on the vocalization of laying hens, and to provide reference for further establishment of a healthy breeding assessment system based on the vocal information from laying hens, the vocalization of laying hens was monitored in this study. The acoustic characteristics of hens raised under cage and perch systems, at the growing stage and laying stage were studied. The experiment was conducted with the same batch of hens (starting from 86 days of age), which had similar body weights (average 1.1 kg) and health conditions. Those laying hens were randomly divided into two groups: 55 layer raised in the perch system and 25 layers in the cage system. The vocalizations of the laying hens were regularly collected from 13 weeks to 42 weeks of age, using National Instruments' PXI-1050 sound measurement system. The captured sounds were analyzed through pre-treatment, feature extraction and data mining algorithms. The spectrum parameters including duration, amplitude, peak frequency, frequency centroid had been used for statistical analysis. The results showed that the typical laying hen's voice could be classified into four types: egg-laying call, singing call, screaming call and fighting call. There were some differences in the vocal recognition process, with overall high recognition accuracy for egg-laying calls (93%), and moderate prediction rate for singing calls (89%), screaming calls (83%) and fighting calls (75%). Most of the sound signals associated with laying eggs are concentrated in the 0.3-20 s range, with peak frequencies in the 2 500-3 500 Hz. The sound signal of the screaming and fighting calls varies from 0.2 to 1.7 s, with the peak frequency mainly ranging from 500 to 4 000 s. Singing calls have a wide range, lasting between 0.2-12 s, and peak frequency ranging from 1 000-4 000 Hz. Compared with laying hens at the growing stage, the duration of vocalization of laying hens at the laying stage was longer, and the values of peak frequency and spectral centroid were decreased, while the sound pressure was slightly increased. It was also found that the peak frequency of laying hens' vocalization was negatively correlated with their age increasing. At 14 weeks of age, the average peak frequency was (2 192±320) Hz; while the average peak frequency was (1 550±345) Hz at 41 weeks of age. The peak frequency decreased by about 44 Hz per week during the growing period and about 15 Hz per week during the laying period. Compared with hens in the cage system, hens in perch system produced more sounds, especially egg-laying and singing sounds. The sound energy of laying hens in perch system was also greater than that of laying hens in cage system. The welfare orientated environment leads to an increase in the frequency of hens' calls, which may also indicate that their vocalization plays a role in natural behavioral expression and social interaction signals. The amount of laying hens call can be used as an indicator to evaluate the welfare of laying hens. In addition, the sound energy of laying hens at night was basically stable (around 1.0 V2·s), unless there were abnormal conditions. According to this phenomenon, the change of acoustic energy amplitude of laying hens can be used as a threshold to monitor and warn the abnormal situation in the laying hens' house during night.