Effects of space allowance on patterns of activity in group-housed dairy calves

With increasing use of social housing for dairy calves, there is a need to refine housing management practices that influence animal behavior and may affect welfare. Our aim was to assess the effect of pen space allowance on activity patterns and pen space use. Holstein heifer calves were group-housed (n = 6 pens; 5 calves/pen) at 14 d ± 2.8 d of age (mean ± SD). After a 7-d adaptation, each pen was exposed to 3 different space allowances (3.7, 4.6, and 5.6 m²/calf) in a random order, according to a replicated Latin square design with three 7-d periods (period 1, d 22–28; period 2, d 29–35; and period 3, d 36–42). Calves were provided milk replacer (12 L/d) ad libitum via an automated milk feeder and gradually weaned over 10 d, beginning at 48 ± 3 d of age. Using leg-based accelerometers (HOBO Pendant G data logger, Onset Computer Corp., Pocasset, MA), we obtained data describing standing time, standing bout frequency, and standing bout duration. Daily pen-level average standing time (6.5 h/d; SE = 0.27) did not differ between treatments. However, with greater space allowance, calves had more frequent standing bouts (22.6 vs. 20.3 bouts/d; 5.6 vs. 3.7 m²/calf; SE = 0.96) of shorter duration. To assess effects of space allowance on within-pen individual variability, we calculated the coefficient of variation for daily activity outcomes at the pen level and intra-class correlation coefficients for hourly standing time, by pen and day. The coefficient of variation for standing behavior outcomes decreased with increasing space allowance, and the intraclass correlation for hourly standing time increased, suggesting that increasing space allowance reduced individual variability and may promote more synchronous rest. Finally, we qualitatively assessed use of pen space using motion heat maps generated using computer vision from video recorded of each pen from 0800 to 1200 h on d 6 and 7 of each experimental period for each pen. These images suggest that calves preferentially used space near the perimeter of the pen, but space was used more uniformly when space allowance is restricted. Overall, these results suggest that lower space allowances may restrict patterns of activity at the pen level and reduce behavioral synchrony.