Several matrices are available to detect the concentrations of cortisol and dehydroepiandrosterone (DHEA) as markers of allostatic load and resilience but most of them provide a measurement of the concentration at a singletime point or within a 12– 24 h period and are subjected to daily fluctuations; conversely, keratinized derivatives,
as hair is, provide a measure of the hormonal concentrations over medium- and long-term periods, appearing unaffected by circadian changes or by factors inducing short-term variations. Aim of this study was to evaluate hair cortisol (HC), hair DHEA (HDHEA) and their ratio (HC/HDHEA ratio) as biomarkers of allostatic load and resilience in sows around farrowing, in relation to four different models of farrowing crates, and in relation to different batches by a non-invasive sampling. The study has been conducted on 296 pregnant sows managed in a batch farrowing system from February to June. Sows were kept in multiple pens of 10–15 sows until 5 days before farrowing, then were randomly divided in 4 different models of farrowing crates. The hair samples were taken by shaving for the first time (ST1) 2.6 ± 1.6 days before the expected delivery date and for
the second time (ST2) 88.9 ± 3.3 days after parturition. The environmental temperature and the relative humidity data were recorded and used to calculate the Temperature Humidity Index (THI). HC and HDHEA were determined using a solid-phase microtiter radioimmunoassay (RIA) while HC/HDHEA ratio has been calculated. No differences in terms of hair steroids concentration were found between the four models of farrowing crates and the sampling times (P > 0.05). The interaction between batch and sampling time has been significant for all the biomarkers considered (HC (P < 0.01), HDHEA (P < 0.05) and their ratio (P < 0.01)). During the pregnancy period in collective pens (ST1) HC/HDHEA ratios were never lower (with an exclusion of February) than those in the following characterized by the early postpartum and lactation in individual crates (ST2). It seems that an aggregate effect of different stressors acts on the sows exhausting their ability to cope with adverse events; it should be further investigated the influence of the social interaction in collective pens that cyclically re-occurs in the standard swine production system.
