The objectives of this study were to, first, examine the factors that influence social rank of captive plains zebra mares, and second, test if high-ranking mares conceive earlier and if they have shorter inter-birth intervals than low-ranking ones. In three herds of captive plains zebra aggressive interactions (biting and offensive kicking) between the mares were recorded. These data were used to determine, for each mare, the total number of mares that dominated her in each period of social stability. The GLMM model revealed that older mares were dominated by a lower number of mares than the younger mares. It was also found that the probability that a mare would conceive declined with the increasing number of dominant mares.