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Environmental sound and animal vocalizations provide non-invasive information for welfare assessment in livestock systems. This systematic review surveys their application in beef and dairy cattle, poultry, and swine, with a focus on environmental noise, vocalizations and the characterization of acoustic sources. Searches in Scopus and Web of Science followed PRISMA guidance and the PICO framework. After applying strict criteria that required peer-reviewed experimental studies in English, quantifiable acoustic data, and clear descriptions of measurement procedures, the review included 36 studies. Four approaches recur: vocalizations as welfare indicators; characterization of acoustic sources; combined analyses of vocalizations and sources; and evaluation of animal responses to acoustic stimuli. Recent work reports advances in recording equipment, signal processing, and precision livestock tools. Important challenges remain, including heterogeneous acoustic metrics, limited physiological validation, and difficulties applying models under commercial conditions. Overall, the evidence supports sound as a candidate for real-time monitoring and highlights the need for accessible, standardized methods. The findings provide a basis for future research and practical applications in welfare assessment.
Niño et al. (Wed,) studied this question.