Cortisol levels in skimmed milk during the first 22 weeks of lactation and response to short-term metabolic stress and lameness in dairy cows

Background:Cortisol is secreted into blood in reaction to acute stress,but also in phases of diminished feed intake and changed animal behavior.As cows do not always show clear signs of discomfort,reliable diagnostic markers could be used to provide information regarding individual cows’ distress.The objective of this study was to establish an ether free immunoassay for the detection of Cortisol and to determine values during the first 22 weeks of lactation.Furthermore,the response in milk Cortisol levels was assessed during times of metabolic stress and pain associated symptoms of lameness.Methods:Milk yield and composition,blood serum glucose,NEFA and BHBA as well as milk Cortisol were determined in 24 multiparous Holstein-Friesian cows over the course of the first 22 weeks of lactation.Animals were further checked for signs of clinical diseases on a daily basis.Two feed restrictions over three days(FR;70%of precious ad libitum intake)were performed during the 4th wk and the 21wk,respectively.An ELISA for Cortisol measurement in easily accessible bovine skimmed milk was established and applied.Results:On the last day of FR in early lactation,a reduaion in milk yield and changes in serum metabolites compared to respective previous values were detected.The FR in mid-lactation resulted in no changes in milk production and serum metabolites.Milk Cortisol was highest during first wk of lactation and remained on comparable levels thereafter.Milk yield and composition were not influenced by FR.Lameness resulted in enhanced milk Cortisol levels.Conclusion:Milk Cortisol could be used as an indicator of painful symptoms such as lameness.Higher values of milk Cortisol levels during first wk of lactation should be taken into account for interpretation.