Endocrine response of gilts to various common stressors: A comparison of indicators and methods of analysis

The first aim of the present study was to determine whether various common events encountered by pigs in commercial farms or experimental units induce activation of the sympathetic and hypothalamo-pituitary-adrenal (HPA) axes. The second aim was to compare the efficiency of various indicators and methods of analysis to detect the occurrence of a stress reaction. Responses to two blood sampling methods, immobilization by snaring, brief electric shocks, loud noise, ear tagging, tattooing, biopsy, pen relocation or delayed feeding time have been evaluated. Series of blood and saliva samplings (from 10 min before to 120 min after stressor application) were collected for each stressor on a total of 8 catheterized sows. Plasma glucose, lactate, cortisol and ACTH levels as well as salivary cortisol were measured. Acute increases of cortisol or ACTH (at least at time points + 5 or + 15 min) were observed for intense noise, electric shocks, ear tagging, tattooing, biopsy, cava blood sampling, snaring and pen relocation. Snaring, relocation and vena cava blood sampling generated longer stress responses whereas delayed meal and tail blood sampling had no influence. Plasma lactate was also significantly increased in several time-points after stressor application contrarily to plasma glucose. Comparison of successive time points with the starting basal level and comparison with the control group were more sensitive methods to detect a stress response to moderate stressors like electric shocks and tattooing, than comparing the area under the curve. These data confirmed that salivary cortisol is a good indicator to measure the HPA response to a stressor, provided that post-treatment levels can be compared with pre-treatment levels.

Research Highlights
► Snaring, relocation and vena cava blood sampling induce strong stress responses in pigs.
► Delayed meal, tail blood sampling and noise are weak stressors.
► Cortisol and ACTH plasma levels are the more sensitive stress markers.
► Measuring cortisol in saliva can be used to evaluate acute stress responses in pigs.