Release of β-endorphin, adrenocorticotropic hormone and cortisol in response to machine milking of dairy cows

Research (Published online: 07-03-2015)

6. Release of β-endorphin, adrenocorticotropic hormone and cortisol in response to machine milking of dairy cows - E. Fazio, P. Medica, C. Cravana and A. Ferlazzo

Veterinary World, 8(3): 284-289

   doi: 10.14202/vetworld.2015.284-289

Abstract

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Aim: 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.

Materials and Methods: A total of 10 healthy multiparous lactating Italian Friesian dairy cows were used in the study. Animals were at the 4th-5th 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 1st and the 2nd day (p<0.05), and a decrease after afternoon machine milking at the 2nd 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 1st and the 2nd 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.

Keywords: adrenocorticotropic hormone, cortisol, dairy cows, machine milking, β-endorphin.