The electrocardiogram of sheep, monitored by radiotelemetry, during electrical or carbon-dioxide stunning and subsequent slaughter.

Abstract

The e.c.g., monitored by telemetry, was used to study changes in the heart activity of sheep bled out after electrical stunning or carbon-dioxide anaesthesia. The decrease in ventricular rate which occurs as sheep are bled out after electrical stunning is apparently attributable to increasingly severe anoxia, rather than to changes in blood pressure. The heart rate at sticking is directly related to the heart rate before electrical stunning, but no relationship was found between the wattseconds used and the heart rate at sticking. However, the greater the number of wattseconds applied, the lower the minimum heart rate recorded after sticking. Exposure to carbon dioxide caused an initial tachycardia, followed by a decreased heart rate and then a secondary increase. The rate rose further when the sheep were removed from the gas. As the percentage of carbon dioxide used increased, the duration of heart activity after sticking decreased. Since high stunning currents cause early atrioventricular block, they might adversely affect bleeding out, if this is dependent on heart activity. High concentrations of carbon dioxide results in earlier termination of heart activity and might affect bleeding out similarly. The lower heart rate of sheep before electrical stunning may indicate that it is inherently less stressful than carbon-dioxide anaesthesia and so less likely to affect meat quality.