Sampling methods for determination of cortisol in pig saliva and their use in the assessment of pig welfare

This study focused on finding new information regarding the assessment of pig saliva cortisol samples in terms of practical effects of the sampling, sample storage conditions, and their laboratory analysis. The study was divided into two experiments. The first experiment was focused on finding the effect of sampling time on cortisol concentrations in pig saliva. The second experiment was focused on determining the effect of storage conditions on the value of salivary cortisol. Before the initiation of the study, we tested which one of the commercially available ELISA kits would be the most suitable for our experiments. Simultaneously, we carried out a pre-study to evaluate the effect of relocation and change in the housing type on the concentration of salivary cortisol in gestating sows. The samples were obtained by oral cavity swabbing, using a standard cotton swab. In the first study, piglets were examined at the age of 4 ± 1 days, and breeding management routine procedures were used as a stress factor. In the second study, the piglets were examined immediately after weaning (at 28 ± 2 days of age). The Cortisol EIA kit was found to be statistically more accurate and thus a more suitable ELISA kit for our experiment. Analysis of the relocation effect and the effect of change in the housing type showed that relocation does not seem to be a stress factor for gestating sows as no significant changes were observed in salivary cortisol concentration (P > 0.5); however, the change in the housing type lead to a significant increase in salivary cortisol (P < 0.001). In the first study, we determined using the ELISA method that the most significant difference occurred in 40 min (P < 0.01), which suggests that the best time for a sampling in order to assess salivary cortisol concentration is 40 min after stress induction by routine procedures. The conclusion of the second study was that in the monitored period of 60 h (P < 0.05), cortisol concentration decreased depending on the storage temperature. The decrease started between 48 and 60 h which showed that cortisol is stable in the saliva sample for at least 48 h. These findings will be further applied in our following studies focused on assessment of salivary cortisol concentration after stress induction.