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 allo ws flexibility for variations in the physical and social environment. The s pace requirement of pigs housed in large groups and on deep-straw bedding h as 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 influe nce 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. 0.7 32 S.E.D. 0.0142 kg/day, P<0.01). Within pen variation in ADG was similar f or each treatment. Number of skin lesions were elevated by low space allowa nce (10.1 vs. 8.5 s.e.d. 0.68 lesions per pig for low and high space allowa nce 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 lar ge groups, and the higher lesion score and suppressed immune response of pi gs provided with lower space allowance, suggest that these conditions may i ndependently compromise productivity and welfare. (C) 2000 Elsevier Science B.V. All rights reserved.