Abstract
Simple SummaryThe measurement of faecal cortisol metabolites (FCMs) is increasingly used to monitor physiological stress responses in different animal species. Before this method is applied in coming stress- and welfare-related studies of farmed blue foxes (Vulpes lagopus), a species-specific validation is first required. In the current study, a 5α-pregnane-3ß,11ß,21-triol-20-one enzyme immunoassay was found suited to measure FCMs and thus hypothalamus–pituitary–adrenal (HPA) axis activity in farmed blue foxes. FCMs can therefore serve as a valid indicator of stress in future welfare studies of blue foxes.Welfare studies of blue foxes would benefit from a measurement of faecal cortisol metabolites (FCMs) as a non-invasive, physiological stress parameter reflecting hypothalamus–pituitary–adrenal (HPA) axis activity. Before implementation, a species-specific validation of such a method is required. Therefore, we conducted a physiological validation of an enzyme immunoassay (EIA) to measure FCMs in blue foxes. Twenty individuals (nine males and eleven females) were injected with synthetic adrenocorticotrophic hormone (ACTH) and faecal samples were collected every third h for two days. The FCM baseline levels were assessed based on the first sampling day (control period, 144 samples), followed by the ACTH injection and the second day of sampling (treatment period, 122 samples). FCMs were analysed with a 5α-pregnane-3ß,11ß,21-triol-20-one EIA. We compared the estimated mean FCM concentrations of the treatment samples to the baseline average. All samples for the two periods were collected at the same time of the day, which enabled to test the data also with an hourly pairwise comparison. With the two statistical approaches, we tested whether a possible diurnal fluctuation in the FCM concentrations affected the interpretation of the results. Compared to the baseline levels, both approaches showed 2.4–3.2 times higher concentrations on time points sampled 8–14 h after the ACTH injection (p < 0.05). The estimated FCM concentrations also fluctuated slightly within the control period (p < 0.01). Inter-individual variations in FCM levels were marked, which highlights the importance of having a sufficient number of animals in experiments utilising FCMs. The sampling intervals of 3 h enabled forming of informative FCM curves. Taken together, this study proves that FCM analysis with a 5α-pregnane-3ß,11ß,21-triol-20-one EIA is a valid measurement of adrenocortical activity in the farmed blue foxes. Therefore, it can be utilised as a non-invasive stress indicator in future animal welfare studies of the species.
Highlights
The blue fox, the blue colour morph of the Arctic fox (Vulpes lagopus) [1], is the most important farmed fox species in the world, with an annual production of more than 10 million pelts [2]
faecal cortisol metabolites (FCMs) concentrations remained above the baseline throughout the treatment period (Figure 1)
Sex had no clear impact on FCM concentrations (p = 0.083, Sheet 1 S1)
Summary
The blue fox, the blue colour morph of the Arctic fox (Vulpes lagopus) [1], is the most important farmed fox species in the world, with an annual production of more than 10 million pelts (in 2019) [2]. The physiological welfare measurements have relied strongly on the functioning of the hypothalamus–pituitary–adrenal axis (HPA; see the references above for examples). The main glucocorticoid secreted by the HPA axis in almost all mammal species, in blue foxes, is cortisol [13]. Baseline cortisol levels have been measured [5,8,9,10] and change after ACTH challenge or an acute stressor [7,9,11,12]. The invasiveness of this tool has been acknowledged already for some time. The stress experienced by repeated blood sampling may in many cases raise questions about its validity as a welfare indicator [13,14,15]
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