Discrepancy between plasma cortisol level and neutrophil-to-lymphocyte ratio in sheep during shearing

Dimitar Gudev, Ivan Yanchev, Marina Dyavolova, Penka Moneva

Abstract: The object of the present study was to investigate the link between adrenal and leukocyte responses to shearing stress in sheep. The primary parameters determined in this study were cortisol dynamics and neutrophil-to-lymphocyte (N/L) ratio in lactating non-pregnant ewes from the Bulgarian synthetic dairy population (n = 20) and non-pregnant ewes from the Ile de France (meat type) breed (n=20) during shearing. The ewes were shorn at the beginning of June. Blood samples were taken before shearing, immediately after shearing and at 3 h following the onset of shearing. Ile de France ewes were divided into two subgroups based on their reactivity to shearing as assessed by cortisol level immediately after shearing. Group I comprised ewes that had high cortisol level (more stress-reactive) and group II comprised ewes that had low plasma cortisol level immediately after shearing (less stress-reactive). Cortisol level in the ewes of Bulgarian synthetic dairy population (BSDP) was higher immediately after shearing (P < 0.001) as compared to Ile de France ewes. Plasma cortisol level in the ewes of Bulgarian synthetic dairy population (BSDP) declined significantly at 3 h after the onset of shearing while at that time, cortisol levels in the other group tended to decline but did not reach level of significance. There was signifi cantly higher N/L ratio in BSDP ewes as compared to Ile de France ewes immediately after shearing. Neutrophil-tolymphocyte ratio increased significantly in both breeds of sheep at 3 h following the onset of shearing. Plasma cortisol levels in the more reactive Ile de France ewes were higher across all measurements as compared to less reactive ewes while N/L ratio immediately after shearing and at 3 h since the onset of shearing was higher in less stress-reactive ewes. These results suggest that the magnitude of cortisol response to acute stress is not matched by a corresponding increase in N/L ratio. The results are interpreted to mean that total plasma cortisol level plays a lesser role than free cortisol in N/L trafficking and that neutrophil elastase-induced cleavage of corticosteroid-binding globulin regulates the amount of free cortisol.

Keywords: breed; cortisol; neutrophil-to-lymphocyte ratio; reactivity; shearing; sheep; stress

Date published: 2019-07-31