Reliability of some endocrine and behavioral indices of stress

M. Krusteva, S. Popova-Ralcheva, D. Gudev, V. Sredkova, P. Moneva

Abstract: This investigation accentuates on the reliability of some endocrine (cortisol and prolactin), behavioral (bleating frequency, prevalence of feed and defense response) and immune (heterophil/lymphocyte ratio) indices of stress. Our study comprised several experimental designs with laying hens, cows, does and kids. We found sizable stress response to blood sampling procedures that was registered as early as the first minutes after catching of the bird. There were pronounced individual differences in stress sensitivity demonstrated by plasma cortisol levels which varied from low to high values. Heterophil to lymphocyte ratio, unlike cortisol began to change after a latent period of 10-15 min. following the start of stress stimuli. When combined with cortisol this ratio allowed us to differentiate stress stimuli induced by the handling procedures from those induced by a certain environmental and technological factors. Plasma cortisol level turned out to be reliable stress indicator in does, previously habituated to blood sampling procedures. However, kid separation at the time of weaning caused significant plasma cortisol enhancement. There was no stress when the kids were prevented from suckling but remained to their mothers. The frequency of bleating did not correspond to plasma cortisol dynamics indicating that it is not reliable stress indicator in this particular case. Exposure of cows to heat stress elicited short-term increase of plasma cortisol followed by a quick decline to values that were within the normal range in spite of the elevated rectal temperature. Plasma prolactin increased and remained high throughout the heat load period. These results demonstrate that plasma cortisol level can not be used as a universal stress-indicator.

Keywords: cortisol; endocrine and behavioral indices; plasma; prolactin; stress indicator

Date published: 2019-10-01