Iidentification of new physiological parameters for monitoring chronic stress in growing pigshair cortisol and chromogranin a

Resumen

During the last few decades, the interest to develop non-invasive techniques to objectively assess animal welfare and particularly stress response has increased considerably. Most of previous studies have focused on finding appropriate indicators to evaluate acute stress, but few attempted to find indicators to measure chronic stress. 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 [(Landrace x Duroc) x Pietrain] entire males subjected to weekly remixing were analysed. The results showed a significant positive correlation of hair cortisol concentration in the different samples taken throughout time. Furthermore, differences were observed in terms of the anatomical region sampled, presenting the dorso-lumbar region higher concentrations compared with the cranio-dorsal region. 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 and salivary CgA 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 reduce stress. 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, samples of hair and saliva at 15, 20 and 24 weeks of age (T0, T1 and T2 respectively) were collected. 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 could be good biomarkers of chronic stress in growing pigs. In the third study, behaviour patterns and performance indicators were analysed in relation to EE and HC as potential stress reducers. 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 weeks), 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 and HC positively influenced animal welfare and performance of growing pigs. The fourth study was carried out with the same animals used in studies 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. Finally, the least important factor was the price. However, the price was an important factor for a segment of consumers with a clear preference for low prices. 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.