Context Specificity of the ANS Stress Response during Two Regrouping Experiments in Goats

Abstract

The aim of this study was to analyze whether the activity of the autonomic nervous system (ANS) differs between two regrouping procedures in goats, which would indicate stimulus specificity of these stressors. Applying two regrouping procedures, we evaluated heart rate and heart rate variability (RMSSD, SDNN, and RMSSD/SDNN). The two regrouping procedures were (1) introduction of individual goats into established groups ("introduction experiment") and (2) temporary separation and subsequent reintegration of individuals from/into their group with two levels of contact during separation ("separation experiment"). In the "introduction experiment," the heart rate of introduced goats while lying decreased continuously from an average 78 to 68 beats/min from before the introduction to the last day of the introduction period. Inversely, RMSSD increased continuously from 41 to 62 ms, which, on its own, would indicate an adaptation to the situation. During the "separation experiment," heart rate while lying was higher when goats were separated in the "acoustic contact treatment" (82 beats/min on average) compared with the "restricted physical contact treatment" (75 beats/min on average). This difference reflected a higher level of arousal during the "acoustic contact treatment." However, heart rate activity did not allow detecting effects of separation or reintegration. Even though it can be assumed that both the separation and introduction of goats are stressful for goats, the ANS reactions observed in this study differed between the two management procedures indicating that the ANS activation was specific to each situation. In addition, we discuss the ANS results in context with earlier findings of variables of the hypothalamic pituitary adrenal (HPA) axis (fecal cortisol metabolites) and behavior (lying and feeding). As correspondence between ANS, HPA, and behavioral reactions was limited both within and across experiments, the results of this study underline the concept that stress response patterns are context specific.

Keywords: HPA axis; behavior; goats; heart rate; heart rate variability; regrouping; stress.

Figure 1

Heart rate of introduced goats. Mean heart rate (beats/minute for each day) of individually introduced goats during lying in the “introduction experiment” before (day -3) and during (days 0, 2, and 4) the introduction period. Box-and-whisker plot: boxes = first and third quartile, thick line = median, whiskers = range from minimum to maximum value. Solid lines = model estimates, dotted lines = 95% confidence intervals.

Figure 2

Heart rate variability of introduced goats. (A) RMSSD (milliseconds) and (B) SDNN (milliseconds) of individually introduced goats during lying in the “introduction experiment” before (day -3) and during (days 0, 2, and 4) the introduction period. Box-and-whisker plot: see Figure 1.

Figure 3

Heart rate of separated goats. Mean heart rate (beats/minute) of separated goats during lying in the “separation experiment” in relation to the “acoustic contact” and “restricted physical contact treatment.” Box-and-whisker plot: see Figure 1.