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The difference between the average time of simulated castration was significant (30 s vs. 20 s); so much so that the castrated animals showed a higher increase in cortisol due to the longer manipulation period or pain, or a combination of the two. There was no significant difference in the pre-treatment, while after the treatment the values rose perceptively in the SIMCAST pigs (from 73,5 nmol/L to 145,3 nmol/L) as well as in the CAST pigs (from 75,4 nmol/L to 357,3 nmol/L), these values being, post-treatment, significantly different. Both the CAST and SIMCAST groups had a significantly increase in their plasma cortisol levels in comparison with the earlier treatment. Also, the CAST pigs presented an increase that was 3.92 times what the SIMCAST values were after treatment. The most probable explanation is that there was a difference in the pain experienced by both groups. This study measured a cleat difference between the animals that experienced stress and those that experienced pain in addition to that stress. .
These results suggest that the level of cortisol, under controlled experimental conditions, is different between the stress of manipulation and that of pain. In comparison to earlier studies, these results show a cortisol response to pain of considerably larger magnitude in comparison to just the stress of castration manipulation. This suggest that cortisol can be a useful tool to distinguish between stress due to manipulation and to pain.
M. Hensch, L.L. Layman, L.A. Karriker, J. Coetzee, A. Johnson. Using serum cortisol to distinguish between acute stress and pain response following castration in piglets. 2010 AASV Annual Meeting: Implementing Knowledge.
