Spoolder, H. A. M., Aarnink, A. A. J., Vermeer, H. M. 2012. Effect of increasing temperature on space requirements of group housed finishing pigs. Applied Animal Behaviour Science 138(3-4), 229-239.
For groups of pigs to cope adequately with their housing conditions they need sufficient static space (occupied by the body of the pig), activity space (for movement between different functional areas and behaviours relating to these) and interaction space (for appropriate social behaviour). Estimates for static space have been presented for thermoneutral conditions, but are expected to increase substantially as temperature increases. The present paper models the relationship between ambient temperatures above the comfort zone, and thermoregulatory lying behaviour in finishing pigs. Estimates of the effect of posture on floor occupation were obtained and presented as ‘k-values’ (k = floor area occupied (m2)/body weight2/3(kg)) to correct for the effect of pig size. A literature review was conducted to collect information on three aspects of lying behaviour: lying frequency, posture (lateral, semi lateral or ventral lying) and level of space sharing (huddling) in response to increasing temperatures. The lowest and highest values found were: increase in lying down: 0.2–0.66%, reduction in space sharing: 1.7–4.9% and increase in lateral vs sternal lying: 0.8–2.3% per °C temperature increase. Extrapolation of k values in the comfort zone to T = 31 °C suggests a range of k-values from k = 0.0331 to k = 0.0385 for static space. In the second part of this paper we analyse video data from a pig building in which groups of 18 pigs were kept in large pens (1.67 m2 per animal) at temperatures ranging from 16 to 32 °C. We find a value of k = 0.0339 at T = 31 °C for static space, which is at the lower end of the range predicted from literature. A possible explanation for this relatively low additional space requirement is that the animals coped by increasingly using the slatted area (with sprinkler system) as a lying area. The study confirms earlier suggestions that the amount of space required by EU legislation is insufficient for pigs at the end of the finishing period, even at relatively low temperatures. In situations where the average room temperature exceeds the comfort zone, pigs need additional space to cope with their housing system, or alternative methods to cool themselves down.