Behavioural and physiolgical thermoregulation in groups of pregnant sows housed in a kennel system at low temperatures

The behavioural and physiological responses of pregnant sows to cold exposure in a kennel system were investigated. Ten groups, each of six pregnant sows, were housed over winter in a non-insulated building containing kennels. Lying posture, social thermoregulation, time spent inside the kennels and general activity were recorded in three 48-h periods with different diurnal room temperatures: cold (-9 to -1 degrees C), medium (0 to +3 degrees C) and warm (+4 to +9 degrees C). Blood samples were collected from two of the groups, and the concentrations of glucose, free fatty acids, total thyroxine (TT4) and free thyroxine (FT4) in the plasma were determined. The air temperature difference in between the surrounding room and the kennels increased with decreasing room temperature with a maximum of 12 degrees C at a room temperature of -10 degrees C. Activity level did not differ significantly between temperature periods (30.6 +/- 1.1%). At all temperature periods, the sows spent between 80 and 90% of their time inside the kennels. The sows spent significantly more time eating/manipulating straw in the cold than in the medium and warm period (P = 0.038). Time spent lying on the belly in body contact with other sows inside the kennel increased significantly from 15.6% in the warm period to 20.3% in the medium period and 44.9 % in the cold period (P = 0.001). The two highest ranked individuals (rank 1 and 2) tended to spend more time inside the kennel than sows with rank order 4 to 6 (P = 0.059). At a diurnal room temperature of -8 degrees C, the sows had a significantly higher level of (FT4) in the plasma than at higher temperatures (P < 0.001). The relationship between the other blood parameters and diurnal room temperature was difficult to interpret. This study suggests that kennels with straw give the sows good protection from climatic conditions, and that social thermoregulation in a micro environment is an important strategy to cope with low temperatures. At a diurnal room temperature of -8 degrees C, however, the increase of FT4 in the plasma may indicate an increased metabolism and thus an increased energy requirement. Since low-ranking individuals spent less time inside the kennels than high-ranking sows, they probably had a greater heat loss. For practical application of the system, the kennel should thus be designed in a way that allows all individuals to get inside.