Identification of new physiological parameters for monitoring chronic stress in growing pigs : Hair cortisol and Chromogranin A

The main objective of this thesis is to identify and study the feasibility and reliability of hair cortisol and salivary Chromogranin A (CgA) as indicators of chronic stress in growing pigs. In this context, four studies were conducted encompassed in two different experiments. The first study aimed to determine the viability of hair as a matrix to detect cortisol in swine. For this purpose, hair samples from 56 crossbred entire males subjected to weekly remixing were analysed. The results showed a significant positive correlation of hair cortisol concentration over time. Furthermore, differences were observed in terms of the anatomical region sampled. According to these results, hair is a proper matrix to detect cortisol in growing pigs. The aim of the second study was to analyse the use of hair cortisol, salivary CgA and tumour necrosis factor alpha (TNF-a) in blood as potential biomarkers of chronic stress. For this reason 56 crossbreed entire males were subjected to different treatments using environmental enrichment (EE) and a compound of natural herbs (HC) aiming to stress reduction. The treatments were: a) pigs reared in EE b) pigs supplemented with HC, c) pigs reared in EE and supplemented with HC (EEHC) and d) control group (CG). During the study, we collected samples of hair, saliva and blood on 15, 20 and 24 weeks of age (T0, T1 and T2 respectively). At T0, no differences were observed in any indicator. However, at T2, salivary CgA and hair cortisol concentration were lower in EE, HC and EEHC compared to the CG. At T1, similar differences were observed, but only in salivary CgA concentration. In addition, the concentration of hair cortisol was significantly correlated with salivary CgA concentration. Results from this experiment suggest that salivary CgA and hair cortisol can be good biomarkers of chronic stress in growing pigs. In the third study, behaviour and performance changes were analysed in relation to EE and HC. For this reason, body weight and body lesions were recorded from all the pigs before starting the experiment (15 weeks old) and at 18, 20, 22 and 24 weeks. Moreover, weekly observations were performed from each pen, and three novel tests were carried out at 16, 19 and 23 weeks of age. At the end of the experiment (24 days), pigs from the control group showed a lower weight than pigs subjected to EE or HC. Furthermore, pigs reared with EE presented more exploratory behaviour and less stereotypies and redirected behaviour. On the other hand, pigs supplemented with HC presented less social interactions and less skin lesions. The results from this experiment suggest that both EE HC positively influence animal welfare and performance of growing pigs. The fourth study was carried out with the same animal used in study 2 and 3. The aim of this last study was to evaluate consumers acceptability, and preference, and meat and carcass quality of pork regarding the EE and HC. In general, there was no significant difference in quality or acceptability of any of the parameters analysed. On the other hand, the most important factor considered by consumers was the production system, with preferences for those systems aiming to increase the welfare, followed by the feeding system, with preference for systems supplemented with natural herbs with relaxing properties. The present results suggest that improvements in animal welfare at farm level are appreciated by an important segment of consumers. In summary, results from both experiments suggest that cortisol measured in hair and CgA measured in saliva could be good chronic stress indicators in growing pigs.