Vocalization of broiler chickens and laying hens as a measure of welfare

The aim of this systematic review was to summarize, analyse, and critically compare studies that assessed
vocalizations of broilers and layers in relation to their welfare status. Automated sound analysis has been
used to monitor the behaviour of animals and their biological responses to external stimuli. The strategy
“PICo” was applied to build the research question. The final keywords chosen for the systematic review
were: (broiler OR chicken) AND (sound OR vocalization OR “voice recognition”). The research was performed
in four different databases: Pubmed, Scielo, Scopus, and Web of Science. A set of 44 papers was obtained.
Selected papers were published from 2000 to 2022. Only 9 papers were published in the first studied decade, from which 8 were developed by European research groups. The first paper developed in a country
outside Europe was published in 2005 by a Brazilian research group. China leads the number of literatures
about sound analysis (18%). In total, 28 papers were related to broilers and 18 to hens. Seventeen distinct
vocalisations could be identified by sound analysis in the selected papers. Of different welfare dimensions
papers mostly focused on good health and appropriate behaviour (13 papers), followed by good housing
(10 papers), and good feeding (8 papers). Most studies focused on the production phase of broilers (37
papers). There were no papers dealing with transport or pre-slaughter conditions. Most vocalization was
recorded continuously (34 papers), and most experiments were conducted in experimental environments
(29 papers). Thus, evaluating broilers` and hens` vocalization by sound analysis has been used to assess
animal`s welfare, mainly in relation to good health and appropriate behaviour, which is a potential tool that
allows continuous monitoring to provide useful information to the farmer.