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.

Climate change has increased rainfall irregularity, making water management critical for soybean productivity. Microalgae-based biostimulants have been proposed to mitigate the effects of water restriction on plant physiology. This study evaluated the effect of foliar application of Scenedesmus obliquus on transpiration and water use efficiency in soybean plants under contrasting water regimes. The experiment was conducted under controlled conditions using the cultivar Embrapa 59 grown in sandy soil (65% sand). A completely randomized design was adopted with four replicates, combining three biostimulant doses (0, 0.3, and 1.2 g L?¹) and two water management regimes (with and without deficit). A 30-day water deficit was imposed from the R1 stage. Transpiration rate (E) and water use efficiency (A/E) were measured using an infrared gas analyzer. Microalgae application significantly increased water use efficiency, particularly under water deficit (up to 250%), and helped maintain transpiration compared to the control. The highest dose produced the most favorable responses, indicating the potential of this biostimulant under water-limited conditions, although further studies are needed to standardize application protocols.