Ethological study of social behaviour of pigs from the point of view of housing restriction
Abstract. Investigations were carried out to observe predetermined forms of social behavior in pigs affected by environmental space restriction. Pens of floor area 3.6 m2, 6.8 m2, and 29 m2 were used in the study. The experimental programme included 150 piglets from 15 litters with their mothers (10 piglets in one litter). In each cage five piglets with their mother were placed. The animals were observed from the day they were born up to the age of 6 weeks and the forms of social behavior were recorded each day 24 hours during the mentioned weeks. The piglets were weaned in the 6th week of their life and were mixed by the previous categorization of piglets. Ethological observations continued by initial way just before weaning. The piglets housed in smaller pens (3.6 m2 and 6.8 m2) showed abnormal development of agonistic behavior in terms of increased level of aggression (Mann-Whittney U test, p < 0.05). In these pens we registered high frequency of cephalic attacks to dorsal, cephalic and anogenital regions of piglets which remained unchanged after 3 weeks of the experimental programme (Wilcoxon, p < 0.05). The development of social learning in the experimental animals was retarded and the development of agonistic behavior and social hierarchy did not re-establish itself even after the 2nd week of the experiment following the dislocation of piglets to the housing space (29 m2).