Wool cortisol concentrations trends in the lamb from birth to slaughter

Over time, cortisol has drawn more and more attention in the research on how the body reacts to stress. Furthermore, it has a catabolic role, in energy mobilisation, and in the immune response, in the activation of processes to defend the organism. This hormone is present in wool, which, differently from other biological samples, allows for an easily sampling procedure and provides a reliable retrospective matrix unaffected by acute stress. The two major goals of this study were to assess cortisol as an index of the activity of the hypothalamic-pituitary-adrenal axis in lambs prior birth to the time of slaughtering by wool in four European sheep breeds and to investigate if an increased HPA axis activity may impact the average daily weight gain in lambs. A total of 97 lambs were involved in the study. Wool samples were collected from the left shoulder of the lambs included in the study in different sampling times (ST): at birth (ST1) and then at 30-day intervals from the same area of skin for a period of up to 120 days of age as re-shaved wool (ST2, ST3, ST4 and ST5). All animals were weighed at birth and the day before slaughter. The wool cortisol was evaluated by the AlphaLISA immunoassay method after having extracted steroids from the samples. The wool cortisol concentrations were affected both by breed (P < 0.01) and ST (P < 0.01). All the breeds considered showed a reduction of the wool cortisol during the experimental period, but with different trends. The wool cortisol at the ST1 and the live weight at birth was negatively correlated (r = −0.574; P < 0.01) as well as the average wool cortisol concentrations without the values recorded at ST1 and the average daily gain (r = −0.542; P < 0.01). The higher concentrations recorded in the sample collected at birth could origin from the progressive rise in foetal plasma cortisol concentrations that have an important role in structural maturation and in the neonatal adaptation to the extrauterine life. The trends of wool cortisol decreasing after birth till four months of age suggest that each breed could have an its own HPA axis setting. Our findings may be related to the idea of animal robustness and the various metabolic tactics used by various breeds to adapt to their environments during evolution. In conclusion, this study underlined a time-specific and a breed-characteristic wool cortisol concentration. Moreover, from the analyses emerged that the wool cortisol at birth and the live weight at birth was negatively correlated as well as the average of the wool cortisol concentrations recorded postnatally and the average daily gain.