UMR1213 Herbivores, Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement - INRAE Theix, F-63122Saint-Genès Champanelle, France.
Animal. 2020 Sep;14(9):1916-1922. doi: 10.1017/S1751731120000695. Epub 2020 Apr 8.
Cortisol is often used as a stress indicator in animal behaviour research. Cortisol is commonly measured in plasma and can also be measured in saliva. Saliva contains only the free form of cortisol, which is biologically active, and saliva sampling is not invasive and may therefore be less stressful. Our study aims to guide the choice between the measurements of cortisol in plasma v. saliva depending on experimental conditions. We analysed the effect of the level of cortisol in plasma on the concentration of cortisol in saliva compared to plasma and the effect of saliva sampling v. jugular venepuncture on the cortisol response. In Experiment 1, blood and saliva were collected simultaneously under conditions in which the expected cortisol release in blood varied: in an undisturbed situation or after the isolation of lambs from their pens or the administration of exogenous ACTH (six animals per treatment). In Experiment 2, we subjected lambs to saliva sampling, venepuncture or neither of these for 8 days to evaluate how stressful the sampling method was and whether the animals habituated to it by comparing the responses between the first and last days (four animals per treatment). All animals were equipped with jugular catheters to allow regular blood sampling without disturbance. Samples were collected 15 min before any treatment was applied, then at various time points up to 135 min in Experiment 1 and 45 min in Experiment 2. In Experiment 1, we observed a strong correlation between salivary and plasma cortisol concentrations (r = 0.81, P < 0.001). The ratio between salivary and plasma cortisol concentrations was 0.106 on average. This ratio was higher and more variable when the cortisol concentration in plasma was below 55 nmol/l. In Experiment 2, venepuncture induced a larger cortisol response than saliva sampling or no intervention on day 1 (P < 0.02); this difference was not observed on day 8, suggesting that sheep habituated to venepuncture. We recommend the measurement of cortisol in saliva to avoid stressing animals. However, when the expected concentration in plasma is below 55 nmol/l, the cortisol in saliva will reflect only the free fraction of the cortisol, which may be a limitation if the focus of the experiment is on total cortisol. In addition, if cortisol is measured in plasma and blood is collected by venepuncture, we recommend that sheep be habituated to venepuncture, at least to the handling required for a venepuncture.
皮质醇通常被用作动物行为研究中的应激指标。皮质醇通常在血浆中测量，也可以在唾液中测量。唾液只含有生物活性的游离形式的皮质醇，且唾液采样无创伤，因此可能压力更小。我们的研究旨在根据实验条件指导选择测量血浆中的皮质醇与唾液中的皮质醇。我们分析了血浆中皮质醇水平对唾液中皮质醇浓度的影响（与血浆相比），以及唾液采样与颈静脉穿刺对皮质醇反应的影响。在实验 1 中，在预期的血液皮质醇释放会变化的情况下，同时采集血液和唾液：在不受干扰的情况下，或者将羔羊从围栏中隔离，或者给予外源性 ACTH（每种处理 6 只动物）。在实验 2 中，我们让羔羊接受 8 天的唾液采样、静脉穿刺或两者都不做，以评估采样方法的压力，并通过比较第一天和最后一天的反应来判断动物是否对此有了适应性（每种处理 4 只动物）。所有动物都配备了颈静脉导管，以便在不受干扰的情况下定期采血。在应用任何处理之前 15 分钟采集样本，然后在实验 1 中最多采集 135 分钟，在实验 2 中最多采集 45 分钟。在实验 1 中，我们观察到唾液和血浆皮质醇浓度之间存在很强的相关性（r = 0.81，P < 0.001）。唾液和血浆皮质醇浓度的比值平均为 0.106。当血浆中皮质醇浓度低于 55 nmol/l 时，该比值更高且更具变异性。在实验 2 中，与唾液采样或不干预相比，第一天颈静脉穿刺引起的皮质醇反应更大（P < 0.02）；第 8 天没有观察到这种差异，这表明绵羊已经适应了颈静脉穿刺。我们建议测量唾液中的皮质醇以避免对动物造成压力。但是，当预期的血浆浓度低于 55 nmol/l 时，唾液中的皮质醇将仅反映皮质醇的游离部分，如果实验的重点是总皮质醇，这可能是一个限制。此外，如果在血浆中测量皮质醇并且通过静脉穿刺采集血液，我们建议使绵羊适应静脉穿刺，至少适应进行静脉穿刺所需的处理。
