Accelerometer-based detection of circadian rhythm disruption in sheep following shearing

. Circadian rhythms regulate physiological and behavioral processes in livestock, influencing welfare, productivity, and adaptation to environmental changes. In sheep, locomotor activity (LA) is a reliable marker of circadian organization and can be continuously monitored using accelerometers. Shearing represents an abrupt management event that alters body insulation and may disturb thermal balance and stress responses, but its effects on circadian rhythmicity have not been quantified. This study aimed to evaluate whether shearing disrupts circadian LA in ewe lambs using continuous accelerometer-based monitoring. . Eleven Rasa Aragonesa ewe lambs were monitored continuously from 48 h before to 72 h after shearing. Circadian parameters were quantified using cosinor analysis, including mesor, amplitude, and acrophase, together with indices of rhythm robustness (Circadianity Index, CI) and day–night differentiation (Diurnality Index, DI). Before shearing (− 48 h and − 24 h), sheep displayed robust circadian rhythms, with mesor values of 0.032–0.033 g, high amplitudes (0.011–0.014 g), acrophases clustered around midday (1237–1318 h), elevated CI values (0.19), and pronounced day–night contrasts reflected by high DI values (0.43). At 24 h post-shearing, LA increased significantly, while amplitude (0.009) and CI decreased compared with pre-shearing values (P < 0.01), and acrophase was significantly delayed to the evening (1849 h; P < 0.01). Day–night differentiation was also significantly reduced (P < 0.001). At 48 h post-shearing, amplitude and CI declined further (0.005; P < 0.001), indicating a marked weakening of rhythm robustness, with acrophase delayed to approximately 2008 h. By 72 h post-shearing, circadian organization was severely disrupted, with minimal amplitude (0.001), near-zero CI, markedly reduced DI, and a significantly advanced acrophase to early morning hours (0407 h). . Accelerometer-based biotelemetry revealed that shearing strongly alters the circadian organization of LA in sheep. The procedure induces acute behavioral activation followed by dampened rhythmic strength and altered phase expression, likely reflecting combined stress and thermal effects. These findings highlight the sensitivity of circadian monitoring through accelerometry for detecting management-induced disturbances in livestock behavior. Incorporating chronobiological approaches into routine welfare assessment could improve understanding of physiological adaptation and support more welfare-friendly management practices in animal production systems.