Effect of person and environment on heart rates in two strains of pointer dogs

Several recent studies have shown that there is a general and marked canine cardiac response to humans and to petting from humans. Additional investigations have suggested that one of the major determinants of such responding is genetic. Some studies have indicated that such a response does not occur in nervous, short-haired pointer dogs. Evidence presented in this study indicates that a heart rate response to person and petting does occur in both the nervous as well as the normal pointer dog, but only when the animal is unrestrained. When placed in a restraining harness, only normal dogs showed a heart rate response to person and the characteristic bradycardia upon petting. Moreover, in this and two other separate experiments in which tones (CS’s) were given, it was observed in both normal and nervous strains that mean baseline heart rates were as much as 40 beats per minute lower in the restrained situation than in the unrestrained situation. These experiments measured retention of cardiac response to aversive conditional signals, since most dogs (9 of 12) had received both tones and shock in a bar jumping-shock avoidance experiment one year previously. However, heart rates varied inconsistently in both magnitude and direction of change upon CS showing little or no retention. These findings clarify ambiguity in previous reports and again show that the restraining conditions in an experiment can constitute a serious stress for the animal and be a major factor in the results.