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 ± 2.1 kg 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: 0.75 m2 (small), 1.25 m2 (medium) and 1.75 m2 (large) per 89.7 kg calf. The experimental design was repeated when the calves average live weight were 128.5 ± 3.4 kg. The size of the lying areas was now increased to 1.00 m2 (small), 1.50 m2 (medium) and 2.00 m2 (large) per 128.5 kg calf, respectively. Resting behaviour was recorded using instantaneous sampling at 10 min intervals for 24 h, whereas all incidents of social interactions and play behaviour were continuously scored for 5 h at the end of each experimental period. Both 100 kg calves and 150 kg calves showed less synchronous lying (100 kg: P < 0.05/150 kg: P < 0.01), decreased recumbent lying time (100 kg: P < 0.01/150 kg: P < 0.05), and increased lying time close to another calf (P < 0.001) on the smallest lying area. Except that 100 kg 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 1.25 m2 to 0.75 m2 per animal for calves with a live weight up to 100 kg and a reduction from 1.50 m2 to 1.00 m2 per animal for calves with a live weight up to 150 kg, 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.