Cortisol measurement in milk but not in hair is related to dairy cow health

The aim of the trial was to assess the relationship between cortisol concentration (in milk - MC and hair - HC) and dairy cows health. Cows were sampled in 6 Italian Simmental (IS) and 4 Italian Holstein (IH) commercial farms, were clinical healthy and between 50 and 270 Days In Milk (DIM). Cows were housed in free stalls with cubicles and milking parlour, had free access to ad libitum total mixed ration (TMR) based on corn silage and their management was similar across farms. Formulated was offered twice a day, after the morning and the afternoon milking. The day of official milk recording, 100 ml of milk samples werecollected from each cow at the morning milking and hair was sampled from the tail switch for cortisol analysis. Blood was sampled before the morning meal. Plasma samples were analyzed for Zn, total protein (TP), albumin, ceruloplasmin (CuCp), haptoglobin (Hp) and paraoxonase (PON): all indices related to the inflammatory response. For statistical analysis, animals were classified for parity with ordinal value of 1 for first calving, 2 for second calving and 3 for cows with more than 2 calvings. A Kmean cluster procedure was used to cluster the animals on the base of haematic parameters in 3 classes representing different animal health levels (C1 = better state; C2 = mild state; C3 = worse state). The effect of animal health class on cortisol concentrations was assessed with an univariate model including also the fixed effects of breed, parity, the interaction of class per breed and the linear relationship with DIM. Cows in C3 showed higher (P<0.01) values of MC than cows in C2 and C1. No significant effects were observed for the breed factor both in MC and HC, whilst a significant effect of parity was evidenced for HC concentrations, with higher values in cows with higher parity number (P=0.000). HC was significantly higher in C1 cows, even though a significant effect of the interaction breed x class was also found. These data suggest that milk cortisol is related to the acute phase response to stress and can be used as a biomarker of short term activation of Hypotalamus Pituitary Adrenal axis (HPA) and as an indicator of lactating cows health condition.Instead, HC is probably an indicator of long-term stimulation of HPA in relation to the environment. These results offer a new perspective for the definition of animal welfare by means of endocrine biomarkers.