The effect of space allowance on performance, aggression and immune competence of growing pigs housed on straw deep-litter at different group sizes

Legislation controlling minimum floor space allowances for pigs rarely allows flexibility for variations in the physical and social environment. The space requirement of pigs housed in large groups and on deep-straw bedding has not been adequately addressed. Pigs, housed on deep-straw for 6 weeks in groups of 20 or 80, were provided with a low (50 kg/m(2)) or high (32 kg/m(2)) space allowance in an experiment of 2 X 2 factorial design replicated four times. Low space allowance, irrespective of group size, did not influence average daily gain (ADG), but tended to improve efficiency of growth (P < 0.1). Groups of 80 pigs had a lower ADG than groups of 20 (0.684 vs. 0.732 S.E.D. 0.0142 kg/day, P<0.01). Within pen variation in ADG was similar for each treatment. Number of skin lesions were elevated by low space allowance (10.1 vs. 8.5 s.e.d. 0.68 lesions per pig for low and high space allowance respectively, P < 0.05). The humoral response to an antigen challenge (Newcastle disease virus) was lower when provided with small space allowance (P < 0.01). Since the main effects did not interact, the poorer ADG of large groups, and the higher lesion score and suppressed immune response of pigs provided with lower space allowance, suggest that these conditions may independently compromise productivity and welfare. (C) 2000 Elsevier Science B.V. All rights reserved.