Effects of rearing system, sex, and age on locomotor activity and circadian rhythms in lambs

Locomotor activity (LA) provides valuable insights into animal welfare and the temporal organization of physiology. This study evaluated the effects of rearing system (with mother vs. artificial), sex, and age (week 1 vs. week 3) on lamb LA and circadian rhythmicity. Lambs were fitted with triaxial accelerometers attached to neck collars, which were worn continuously for 7 d. LA was recorded and analyzed based on an ANOVA and cosinor rhythmometry. Activity (counts/min) was significantly (<i>p</i> < 0.001) higher in the day (154.3 ± 3.6) than they were at night (114.5 ± 2.9). Artificially reared lambs were significantly (<i>p</i> = 0.041) more active (159.3 ± 8.2) than were maternal-reared lambs (143.2 ± 7.3) in week 1, but not in week 3. In week 1, in the artificially reared group, females were significantly (<i>p</i> < 0.001) more active than were males (192.0 ± 8.2 vs. 126.5 ± 7.1). Cosinor analysis revealed an overall MESOR (Midline Estimating Statistic of Rhythm), of 131.7 ± 2.8, an amplitude of 36.4 ± 3.1, an acrophase around 15 h, and a robustness of 0.29. In conclusion, accelerometry was an effective tool for quantifying LA dynamics in lambs and can be useful in welfare assessment and precision management. LA was influenced by age and sex, with transient effects of rearing system in early life, and a maturation of circadian rhythmicity by week 3 of age.