Introduction

In the course of a longitudinal study on social stress in female Guinea pigs [1] we developed a simple and noninvasive method to estimate the heart rate during a standard laboratory handling procedure. The method had to meet the following requirements:

• many animals (>20) had to be measured daily within a short time,
• the measure had to be highly standardized which means without manual restraint,
• because it was performed during a lifetime study, the procedure must not involve additional manipulations of the animals, and
• less financial and time effort.

Method

The investigated animals were familiar with a daily standard procedure which included weighing in a plastic basin since their first day of life. In order to avoid disturbing the animals we used this procedure as base for our heart rate measurement: The head of an electronic stethoscope (Bosch, Germany) was built in the weighing basin in a way, that it was directly under the chest of the Guinea pig (figs. 1 and 2). By using an underneath accessible adjusting device the stethoscope’s head could always be adjusted in an optimal position without touching the respective animal with the hands. The electronically amplified heart rate sounds and the animal’s identification were recorded with a commercial two-speed dictation machine (Sanyo, Japan).

A measuring period of 30s proved to be sufficient for reliable results. The evaluation of the heart rate (beats per minute) was done with the help of the program The Observer (Noldus, The Netherlands). The heart beat sounds were played with half speed while a trained person had to press a key synchronously with the beats until the program ended the recording after 60 s.

Results

• The reliability of several measures performed by the same person was higher than 95%.
• The estimated heart rate of non-pregnant female controls is in good accordance with literature [2].
• The heart rate of female Guinea pigs rises during pregnancy.
• The heart rate in animals which were stressed by manipulation of their groups was significantly higher, than in controls.

References

1. Beer, R. (1997). Social stress in female guinea pigs exposed to lifelong daily change of social environment. In: Proc. Int. Congress of Stress: Stress of Life - Stress and Adaptation from Molecules to Man (Budapest, Hungary, 1-5 July 1997).
2. Wagner, J.E.; Manning, P.J. (1976). The Biology of the Guinea Pig. Academic Press, New York.