Social dominance in swine

Data on social dominance value (DV) of 1629 Duroc and Hampshire pigs were obtained from Iowa State University's swine irradiation project. Two measures of DV were analysed within subclasses differentiated by irradiation treatment of sires, and breeds. The analysis of DV was done on a within-litter basis as pigs were raised in litter groups. Angular dominance value (the proportion of animals dominated, transformed to angles) and least-squares dominance value (the result of least-squares minimization of d ij — (DV i — DV j) where d ij is the observed difference in DV between animals i and j) were highly correlated within sex, within litters. Evaluation of pigs was practically identical by the two methods. Barrows were more dominant than gilts. The sex difference was larger in Hampshires than in Durocs. Scrotal irradiation of sires increased the variance component for interaction of sire by sex and increased variance within litters. Within sex, within litter, DV was most significantly correlated with weight at all ages. It was not correlated with backfat thickness if weight was held constant.