Radiotelemetry of Electrocardiogram during Copulation in Animals

I. Observations on Percheron and Thoroughbred Stallions

Abstract

Concerning the heart function during copulation in mammalian, there are few reports on dogs and human such as the heart rate shows a remarkable increasing toward the orgasm. In large domestic animals, however, no observation of heart rate during copulation have been reported nevertheless their sexual behaviour have been well described on several textbooks. Since recent development of medical electronics, it become capable to obtain easily several physiological informations in physiology and clinical medicine using of telemetric techniques. Electrocardiographical change during excercise in race horses have been reported by several authors. From their investigations, heart rate change in various stages of excercise have been demonstrated clearly as well as in changes of ECG pattern. In the present experiment, a set of radioelectrocardiograph (Fukuda Denshi Co. Tokyo) and a plate type electrode designed by TOO et al (1967) were used. Experimental animals used in this investigation were Percheron stallion (7 years old) and Thoroughbred stallion (9 years old) respectively. A bipolar lead (Apex-Base) was applied for taking ECG through the whole course of the copulation. From ECG tracings, changes of heart rate and ECG pattern following male sexual behaviour were studied.
In Percheron stallion, 6 trials of copulation were recorded. Heart rate in resting state which the stallion staying in the stable was counted as 30-40 per minute. When the stallion moves to place for mating where fence around from the stable and walks surround female in the place, the heart rate showed about 70 per minute. During courtship, remarkable fluctuation of heart rate with severe irregularity was observed.This due to sniffing of the stallion and thought to be effected by deep inspiration. Starting the mounting, the heart rate showed sudden increase within short time (15-45 sec.) and it rearched to 150-170 per minute, which is comparable to 70 per minute as a before value. By this time, intromission of the penis and pelvic oscillation are included. Soon after the ejaculation was seen. Duration between start of mounting to the ejaculation was variable ranged with 35-57 seconds. The shortest R-R interval was recorded in every 6 trials at the ejaculation or between the ejaculation to dismounting. The shortest R-R interval was maintained for 35 seconds. After dismounting the heart rate decreased rapidly until the heart rate rearches to a level of about 120 per minute. Then the heart rate gradually decreased toward the value of resting state. It needed about 3-10 minutes for recover from higher level to near value in resting stage. Length for recover from higher level was varied by a condition of the stallion after copulation. When the stallion was less excitability the heart rate return to before value within short time, in contrast, however, when the stallion was excite himself again the time was prolonged. A typical diagram of the heart rate change is shown in the figure. Ventricular extrasystoles at mounting and soon after dismounting, changes of T wave with high amplitude parallel with tachycardia and elevation of ST-T were respectively observed.
In Thoroughbred stallion, only one trial was carried out. Heart rate at resting state in stable was less than 60 per minute. When a mare gives a loud neigh at distant place, the heart rate of the stallion increased temporary to 130 per minute. After then the stallion started to place for mating. In the place, facing to the female, the stallion showed remarkable excitability, the heart rate increased rapidly to peaked value of 170-180 per minute. After the peak, the heart rate decreased gradually and the mounting was done at 115 per minute of the heart rate. The value increased slightly to 130 per minute by mounting and followed ejaculation. After dismounting, the heart rate decreased 80 per minute.