THE EFFECTS OF SOCIAL HIERARCHY IN A DAIRY CATTLE HERD ON MILK YIELD

The objective of this study was to determine the effects of dominance hierarchy in a dairy cattle herd on milk yield. Observations of social behaviors in a group of 126 Polish Holstein-Friesian cows were carried out for seven days, starting from the first grazing day. In order to estimate the position of each animal in the herd, the interactions and relationships between cows were studied. The indices of aggression, dominance and social rank were calculated. These data were used to calculate the competitive index, which enabled to divide all animals into the following subgroups of dominance: dominant cows, subdominant cows, subordinate cows, submissive cows and marginal cows. All dairy cows were at a similar age. Their social rank was found to be positively correlated with body weight and condition. Higher-ranking animals were characterized by a higher milk yield. Both social status and performance parameters may provide a basis for selecting animals and placing them into groups, so as to optimize milk production.