Locomotor activity measured by actigraphy as a means of estimating social mixing and animal density-induced stress in lambs
Abstract
This study aimed to determine whether social mixing and density-induced stress affect locomotor activity in lambs. Eighteen 50-70 d lambs on a commercial farm were fitted with accelerometers for nine days. Lambs were housed with another 25 lambs in a 64- m2 pen (density: 0.40 lambs/m2; farm phase, FP). After nine days, lambs were transported to a feedlot and had the sensors affixed for another nine days. The 43 lambs were pooled with another 25 lambs that came from other farms, and were housed in a 10 x 10-m pen (density: 0.67; low-density phase, L-DP). After 5 d, another 49 lambs were added to the pen (density: 1.21; high-density phase, H-DP). Activity rates did not differ between FP and L-DP; however, lambs were less active in the H-DP than in the L-DP. Activity did not differ between males and females. The proportion of the lambs that exhibited a 24-hour circadian rhythm was higher in the FP than in the L-DP and the H-DP, which differed from each other. In conclusion, social stress, caused by social mixing and high densities can affect the locomotor activity and disrupt the circadian rhythms of lambs. This study demonstrated the usefulness and feasibility of using sentinel animals (fitted with sensors) in commercial feedlots to monitor changes in activity so that measures can be taken to improve animal welfare if necessary. Future studies should investigate the effects of disruptions in circadian rhythms on the immune response and weight gain of lambs under commercial conditions.
