Because cortisol is secreted in
a pulsatile fashion with mean pulse intervals of approximately
120 min, single blood samples do not provide adequate
information [6]. Thus, cortisol in milk could
provide information on the average levels in blood. Concentrations
of functional unbound cortisol in milk and
plasma are related very closely (0.96) independent of the
milk yield. Because binding to globulins prevents passive
transfer into milk higher amounts of non-functional
bound and total cortisol are found in blood in comparison
with milk [7]. Increases of cortisol in blood due to acute
stress are reflected by steadily increasing levels in milk
which in turn decrease as blood levels do. Therefore, a
short peak in cortisol release until 4 h before milking does
not affect its concentration in milk