Time budgets and adrenocortical activity of cows milked in a robot or a milking parlour: interrelationships and influence of social rank

Adrenocortical activity and time budgets in a robotic milking system in two variants of cow traffic (partially forced, free) were compared with a conventional milking system, focusing on the relationships between adrenocortical activity, time budgets, and social rank of the cows. Both groups were housed in identical conditions and consisted of 30 cows each. Within each experiment, direct observations of social behaviour and 24-hour video recordings were conducted during six two-day blocks. We calculated the dominance value and the time budget ('lying, 'feeding', other activity) of each cow. Faeces from each cow were collected to determine the concentration of cortisol metabolites (CCM) as an indicator of baseline adrenocortical activity and possible chronic stress. Analysis of CCM and time budgets did not indicate any adverse effects of the robotic milking system, with one exception: under partially-forced cow traffic, cows of low social rank had longer waiting times in front of the robot. Considering the fact that the number of cows milked by the robot was less than half of that recommended by the manufacturers, our results do not exclude the possibility that a higher stocking rate may lead to further adverse effects.