Use of a conditioned stimulus to study whether the initiation of electrical pre-slaughter stunning is painful

In an attempt to determine whether electrical pre-slaughter stunning is painful, sheep were conditioned to expect stunning by exposure to a light for 5 sec before the current was applied. Sheep in five groups received 90 V, 50 Hz, for 3, 6, 9, 12 and 15 sec, respectively. The heart rate, packed cell volume (PCV) and plasma glucose levels were used to assess the physiological response of the sheep to electrical stunning. After daily exposure to this regime for eleven days, the light stimulus was applied, but was not followed by stunning. The heart rate was not affected by the light. Both PCV and plasma glucose levels showed marked increases when stunning followed exposure to the light. Neither value rose on the twelfth day, when exposure to the light was not followed by stunning. It is concluded that the initiation of electrical stunning was not a painful experience to the sheep in this experiment. No attempt was made to assess the depth or duration of insensibility following stunning.