title: Release of β-endorphin, adrenocorticotropic hormone and cortisol in response to machine milking of dairy cows.
abstract: OBJECTIVE
  The present study was undertaken with the objective to obtain insight into the dynamics of the release of β-endorphin, adrenocorticotrophic hormone (ACTH) and cortisol in response to machine milking in dairy cows.
  
  
  METHODS
  A total of 10 healthy multiparous lactating Italian Friesian dairy cows were used in the study. Animals were at the 4(th)-5(th) month of pregnancy and were submitted to machine milking 2 times daily. Blood samples were collected in the morning: In baseline conditions, immediately before milking and after milking; and in the early afternoon: In baseline conditions, before milking and after milking, for 2 consecutive days. Endocrine variables were measured in duplicate, using a commercial radioimmunoassay for circulating β-endorphin and ACTH concentrations and a competitive enzyme-linked immunoassay for cortisol concentration.
  
  
  RESULTS
  Data obtained showed a similar biphasic cortisol secretion of lactating dairy cows, with a significant increase of cortisol concentration after morning machine milking, at both the 1(st) and the 2(nd) day (p<0.05), and a decrease after afternoon machine milking at the 2(nd) day (p<0.01). One-way RM ANOVA showed significant effects of the machine milking on the cortisol changes, at both morning (f=22.96; p<0.001) and afternoon (f=15.10; p<0.01) milking, respectively. Two-way RM ANOVA showed a significant interaction between cortisol changes at the 1(st) and the 2(nd) day (f=7.94; p<0.0002), and between the sampling times (f=6.09; p<0.001). Conversely, no significant effects of the machine milking were observed on β-endorphin and ACTH changes, but only a moderate positive correlation (r=0.94; p<0.06) after milking stimuli.
  
  
  CONCLUSIONS
  A wide range of cortisol concentrations reported in this study showed the complex dynamic patterns of the homeostatic mechanisms involved during machine milking in dairy cows, suggesting that β-endorphin and ACTH were not the main factors that caused the adrenocortical response to milking stimuli.
authors.affiliation: Department of Veterinary Sciences, University of Messina, 98168 Messina, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Fazio
authors.affiliation: Department of Veterinary Sciences, University of Messina, 98168 Messina, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Medica
authors.affiliation: Department of Veterinary Sciences, University of Messina, 98168 Messina, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Cravana
authors.affiliation: Department of Veterinary Sciences, University of Messina, 98168 Messina, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Ferlazzo
keywords: adrenocorticotropic hormone; cortisol; dairy cows; machine milking; β-endorphin