Influence of Excitability Rate on Physiological Responses to Stress in Goats

SIMPLE SUMMARY: Individual differences in excitable temperament and its effects on physiological stress responses are not adequately studied in goats. This experiment was conducted to determine if the temperament of goats affects their physiological responses when exposed to stress. Intact male Spanish goats were rated for excitability based on a three-point scoring system with a higher score (excitability score, ES) representing a more excitable temperament. Goats were then subjected to one of three treatments (TRT) for 90 min: (i) isolated in an open pen with metal grill panels, (ii) isolated in a pen with side panels covered using tarp sheets, or (iii) maintained as controls with no isolation. Overall plasma cortisol concentrations were the highest in goats with ES 3. Goats with ES 1 had the lowest plasma glucose and non-esterified fatty acid concentrations. Neutrophil–lymphocyte ratio was also the highest in the ES 3 goats. There is evidence that calm goats had lower physiological stress responses compared to goats with excitable temperament. ABSTRACT: This study was conducted to determine if excitability score (ES) in goats can influence their physiological responses when subjected to stress. Thirty-six intact male Spanish goats (8-mo-old) were individually weighed and scored for excitability: 1 for calm (13 goats), 2 for moderately excitable (11 goats), and 3 for highly excitable (12 goats). To impose stress, goats were assigned to one of three treatments (TRT) for 90 min: (i) isolation in an open pen with metal grill panels, (ii) isolation in a pen with side panels covered using tarp sheets, and (iii) no isolation (control). Blood samples were collected at 0, 30, 60, and 90 min of isolation and physiological data were analyzed using MIXED procedures in SAS. The data from the two isolation treatments were pooled and compared with that of the control group. Plasma cortisol and non-esterified fatty acid concentrations were the lowest in goats with ES 1 (p < 0.05). Neutrophil–lymphocyte ratios were also the lowest in goats with a calm temperament (p < 0.01). Application of full quadratic model using response surface methodology (PROC RSREG) in SAS revealed that the influence of ES on physiological stress responses over time was not the same between the TRT groups. The results indicate that physiological stress responses are greater in goats with an excitable temperament compared to goats with a calm temperament.