SOCIAL-ORGANIZATION STRUCTURES IN INTENSI VELY KEPT PIGS .3. ETHOLOGICAL INVESTIGATIONS ON THE RANK ORDER

The rank order of weaning piglets and growing pigs can be characterize d as a social organization structure and a dominance hierarchy, based on agonistic interactions between the animals. Following some introduc tory considerations on the problems of adaptive mechanisms in animals and the concept of social dominance, the present paper deals with the structure, stability and development of the social rank order in 20 gr oups (10 animals/group) of intensively kept pigs. Sociometric characte ristics of different types have been elaborated (individual values of dominance, values of paired comparisons, values of strength and stabil ity of dominance orders). Relevant data were collected around weaning (42nd day of life) and the beginning of fattening (98th). Both, a cran ial position and a high stability within the sucking order were advant ageous for reaching more favourable rank positions in the pen area aft er weaning. Especially after weaning and regrouping the animals showed self-motivated behaviour to establish and maintain a system of domina nce, significantly related with body weight and serum content of gamma -globulins. The rank order was characterized by short-term relations w ith a modest stability and a high instability in the long term. Rank r elations which could be observed were particularly of the bidirectiona l type, showing an increasing part of situation-dependent rank relatio ns. The degree of the characteristics describing paired comparisons wa s generally decreasing with increasing age of the pigs. Results obtain ed are depicted in detail and discussed from an ethological point of v iew.