Resting pattern and social behaviour of dairy calves housed in pens with different sized lying areas

The aim of the present study was to investigate how the size of the lying area influences resting and social behaviour of calves. Thirty weaned dairy calves with an average live weight of 89.7±2.1kg at the start of a 14-days long experimental period, were divided into six groups of five animals. The calves were systematically rotated between three pens with different sized lying areas: 0.75m² (small), 1.25m² (medium) and 1.75m² (large) per 89.7kg calf. The experimental design was repeated when the calves average live weight were 128.5±3.4kg. The size of the lying areas was now increased to 1.00m² (small), 1.50m² (medium) and 2.00m² (large) per 128.5kg calf, respectively. Resting behaviour was recorded using instantaneous sampling at 10min intervals for 24h, whereas all incidents of social interactions and play behaviour were continuously scored for 5h at the end of each experimental period. Both 100kg calves and 150kg calves showed less synchronous lying (100kg: P <0.05/150kg: P <0.01), decreased recumbent lying time (100kg: P <0.01/150kg: P <0.05), and increased lying time close to another calf (P <0.001) on the smallest lying area. Except that 100kg calves spent less time lying close to other calves on the medium-sized lying than on the large lying area, there were no favourable effects of increasing the lying area from medium to large. To conclude, a reduction of the lying space allowance from 1.25m² to 0.75m² per animal for calves with a live weight up to 100kg and a reduction from 1.50m² to 1.00m² per animal for calves with a live weight up to 150kg, decreased the occurrence of synchronous resting, lowered the calves possibility to lie in a relaxed recumbent posture with legs stretched out, and increased the occurrence of calves resting in close proximity to others. The results should be taken into account when designing pens for calves.