Hair cortisol: an indicator of HPA activity in relation to environmental perception in New Zealand White rabbit.

After rodents, lagomorphs constitute the vast majority of subjects used in mammalian experimentation and rabbits are often used as animal models in surgery. Animal welfare in laboratory animals is governed by national and European laws; teams composed by different professionals with adequate knowledge and training must ensure it. The pursuit of animal welfare can also be facilitated by the introduction of an assurance system as good laboratory practice (GLP). The rabbit being a very sensitive species, the methods described above may not be adequate because the perception of environmental stressors may be evaluated anthropomorphically. To date, cortisol assessment in hair samples has been reported as a validated method to evaluate hypothalamic-pituitary-adrenal (HPA) axis activity in different species. The objective of this study was to evaluate HPA axis activity in rabbits before, during and after surgery (dorsal arthrodesis) by measuring hair cortisol. Six prepubertal female NZW rabbits were subjected to dorsal arthrodesis performed after a period of acclimatization that lasted 45 days from their arrival at the enclosure. Hair samples were shaved from the thigh region immediately before surgery. After surgery, at intervals of 40 days, new hair growth was collected from the same area for a period up to 405 days since the rabbits arrived to the enclosure. After methanolic extraction hair cortisol concentrations were determined by RIA. Mean hair cortisol concentration in rabbits at first sampling (before surgery, after acclimatization) was 1.45 ± 0.07 pg/mg (mean ± SE) but at the second sampling (40 days after surgery) it rose (P<0.05) to 4.35 ± 1.16 pg/mg. After 80 days from surgery the mean concentration decreased to 1.47 ± 0.50 pg/mg (P<0.05) and remained stable (P>0.05) for a period lasting until 240 days since the surgery. At day 280 hair cortisol concentrations rose (P<0.05) to 3.34 ± 0.61 pg/mg. Similar (P<0.05) high levels were recorded at day 320 from the surgery that than decreased (P<0.05) to 1.25 ± 0.17 pg/mg at the last sampling. Concentrations at the first sampling were considered basal levels because of the long period of acclimatization undergone by the rabbits. At the second sampling hair cortisol concentrations were significantly higher than those recorded before and this could have been due to the surgical stress suffered by the rabbits previously. This was followed by a return to basal hair cortisol levels, which remained stable for several months. It seems that during that period the rabbits’ HPA axis was not stimulated until the new rise caused by a change of the enclosure operator. This modification activated the HPA axis as recorded by hair cortisol. At the last sampling hair cortisol concentration had dropped again to basal levels. These results indicate that hair cortisol reflected similar levels of activation of the HPA axis in response to two types of apparently different stressor, suggesting that environmental stressors may have been evaluated anthropomorphically. Hair cortisol, not affected by acute stress or by circadian rhythms, could be an additional important tool in animal welfare evaluation.