Physiological response to isolation in Merino ewes of differing temperament

Abstract

This study was conducted to determine whether physiological responses to stress differed between ewes of calm and nervous temperament. Merino ewes were selected for temperament based on agitation score. This score involved placing the ewe inside a 1.5 x 0.7 x 1.5m isolation box for 30 seconds whilst objectively recording movement and sound. Ewes classified as calm had an average agitation score of 18.1 ± 4.8 (n = 15) whilst those deemed as nervous averaged 81.3 ± 4.3 (n = 15). Prior to sampling, ewes were group housed within a yard, fed at the same time and run through a race daily to accustom them to handling. After the acclimatisation period, ewes were quietly restrained and a 9ml venous blood sample was collected. At the same time the following day, ewes were placed inside a replica isolation box for two minutes after which time a 9ml venous blood sample was collected once more. Blood samples were analysed for glucose, lactate, cortisol and differential blood cell counts. Analysis of data was performed using SAS software (version 8.1) with temperament, treatment and the interaction between the two fitted as fixed effects. There was no effect of temperament on blood glucose, lactate or cortisol levels, however after the application of the isolation box test ewes displayed a 27% increase in plasma glucose (4.1 ± 0.18nmol/L prior to isolation and 5.24 ± 0.18nmol/L post isolation; P < 0.001) and a 70% increase in plasma cortisol (47.14 ± 8.4nmol/L prior to isolation and 80.2 ± 8.4nmol/L post isolation; P < 0.001). Plasma glucose and cortisol concentrations were related (r= 0.6, P < 0.05). Differential blood cell counts were not affected by temperament or isolation box test. It is concluded that a ewe's temperament cannot be predicted by the blood measures investigated in this study.