The changes of plasma cortisol and Met-enkephalin in sheep during machine milking

This study was designed to compare the amount of cortisol, Met-enkephalin and glucose that are present in plasma under basal conditions and during machine milking in ewes. The experiment was carried out on non-lactating, one-year-old sheep serving as the control, group and on suckling and machine milking ewes in the middle of lactating period. Machine milking significantly increased the plasma level of cortisol and decreased the Met-enkephalin level. Suckling ewes showed a slight increase in plasma cortisol level and a transient increase in Met-enkephalin level. The plasma levels of both hormones did not change in non-milking sheep during the whole experiment. Unexpectedly, plasma level of glucose did not exhibit any changes during the entire procedure in any of the tested groups. The results suggest that both procedures, machine milking and isolation of ewes from their lambs, are stressful and can alter the plasma hormone levels.