The development of sleep-like posture expression with age in female Holstein calves.

Sleep plays an important role in cattle production and welfare. Therefore, this study aimed to investigate the development of sleep-like posture (SLP) expression in dairy calves from birth to the first calving as an indicator of their sleep behavior. Fifteen female Holstein calves were subjected. Daily SLP was measured eight times (0.5, 1, 2, 4, 8, 12, and 18 months and 23 months or 1 month before the first calving) using an accelerometer. Calves were kept in individual pens until weaning at 2.5 months old and then kept in the group. The daily SLP time decreased rapidly in early life; however, the rate of decrease gradually slowed and eventually reached a stable level of approximately 60 min/day after 12 months old. The daily SLP bout frequency showed the same change as the SLP time. In contrast, the averaged SLP bout duration slowly decreased with age. Longer daily SLP time during early life in female Holstein calves might be related to brain development. The individual expression of daily SLP time differs before and after weaning. Some external and/or internal factors associated with weaning may be involved SLP expression.