Lying behaviour and adrenocortical response as indicators of the thermal tolerance of pigs of different weights
The aim of this study was to assess optimal temperature ranges for fattening pigs of different weights kept in pens with partially slatted floors. We examined the behavioural and adrenocortical responses of pigs of different weights (25–35 kg, 50–70 kg, and >85 kg) to
a wide range of ambient temperatures (2–29°C). On three days of each experimental period, we took saliva samples for the analysis of cortisol concentration, and recorded lying behaviour from 0800–0600h. Behavioural and cortisol parameters were analysed using linear mixed effects
models. Optimal temperature ranges for the three weight-classes were calculated using logistic regression. Pigs chose different areas for resting depending on ambient temperature. With increasing temperature, pigs used the dung area more often and lay more often without contact with pen mates.
Compared to lighter pigs, heavier pigs lay without contact with pen mates at lower temperatures. In general, lying without contact occurred at temperatures 5–7°C lower than lying in the dung area. Huddling increased with decreasing temperature, and, with increasing weight, pigs showed
huddling at lower temperatures. There was a significant increase in cortisol levels at high ambient temperatures in pigs >85 kg. In pens with partially slatted floors, the results indicate temperature ranges within the thermal tolerance of pigs to be 19–21°C for pigs weighing
25–35 kg (lying area of 0.46 m2/pig), 10–17°C for pigs between 50–70 kg and 5–17°C for pigs >85 kg (both weights: lying area of 0.67 m2/pig).