Measuring lamb activity during lactation by actigraphy

Twenty-two lambs were used to determine their locomotor activity during lactation, and its circadian rhythm, based on data collected by actigraphy; the relationships among lambs were also measured calculating their proximity and distance. Lambs were fitted with Bluetooth-enabled (BT) accelerometers during weeks 1 and 4 of age, and data were downloaded as activity counts at 1-min intervals (Vector Magnitude, VM). Sensors were programmed as receivers and as beacons of the BT signal to calculate proximity (min/h) and distance (m) to another lamb. For each week, mean daily VM was calculated at hourly intervals. Circadian rhythms in VM were graphed by fitting the time-series measurements of each lamb to the cosine curve of a 24-h activity rhythm. Week of lactation and lamb sex had a significant (P < .05) effect on VM. Lambs had a higher (P < .05) VM (counts/min ±S.E.) in week 1 (154 ± 13) than in week 4 (117 ± 4), and female (113 ± 10) were more active (P < .01) than male lambs (113 ± 10). Twin lambs spent more time (P < .001) close to its sibling than to another lambs. Lamb activity followed a 24-h rhythm in week 4, only. In conclusion, actigraphy demonstrated that circadian rhythms in activity were not present in the first week of life, and twin-born lambs had stronger associations with their littermates than did singletons with other lambs, which reflected the strong bond that is established between twin lambs.