Linear regression between fecal cortisol metabolites and circulating cortisol levels of peri-partum ewes: Suggesting a non-invasive alternative sampling method

The protection of animal rights is essential when conducting sampling, and it is crucial to develop and use noninvasive sampling methods. Therefore, this study evaluated fecal cortisol metabolites (FCMs) in ewes around parturition as a noninvasive method and an alternative to invasive blood sampling for assessing blood cortisol concentrations. An important objective of the present study was to obtain regression equations to estimate serum cortisol concentrations according to the measured FCMs. For this purpose, from 45 days before to 45 days after parturition, blood and fecal samples were taken every two days from 35 adult pregnant ewes. Serum cortisol levels and FCMs were assessed in all samples. There was a positive and significant correlation between serum cortisol and FCMs in the entire study. Furthermore, a linear regression formula was defined between these parameters, and an estimated value of each parameter can be obtained by substituting one parameter in the formula. The evaluating FCMs has several advantages over the analysing blood cortisol, including convenience and stress-free sampling in animals. The animal rights are respected due to the lack of need for blood sampling, thereby providing the possibility of multiple non-invasive sampling at different periods. Using the results of this study, the evaluation of FCMs in sheep can be considered as a reliable alternative for blood sampling. •Cortisol is an index for stress and metabolic disorders in sheep.•Blood sampling to evaluate circulating cortisol is difficult and may violate animal welfare.•The current research suggests a non-invasive method to evaluate blood cortisol by analyzing fecal cortisol metabolites (FCMs).•The presented regression formulas may be useful to estimate blood cortisol levels by putting FCMs in them.