Head-only electrical stunning of sheep: Variations in electrode positions and their impact on the effectiveness of the stun (MSc)

Traditional sheep slaughter usually involves the animals being initially stunned using head-only electrical stunning and then slaughtered by exsanguination. Current welfare legislation requires the electrodes to be applied in a position that spans the brain. In terms of animal welfare, an optimum position of between the eye and the base of the ear on each side of the head is recommended.

In manual head-only electrical stunning of sheep that are free-standing within a group in a stunning pen, deviations from this position are, however, likely to occur.

This study aimed to assess whether variations in electrode positions can have an impact on the effectiveness of the stun in this method of sheep stunning, as well as whether the amount of wool present in the application sites of the electrodes can have an impact. Three abattoirs, named as Abattoirs A, B, and C were visited. For each sheep, the electrode position and the amount of wool was assessed using scoring systems of seven and five scores, respectively. The signs of an effective stun were also assessed and various electrical parameters were measured. The impact of electrode position and the amount of wool on the effectiveness of the stun was assessed only in Abattoir C, as all of the sheep were stunned effectively in Abattoirs A and B, but their impact on the electrical parameters was assessed in each abattoir.

The study found that, in Abattoir C, the electrode position had a significant impact (P<0.05) on the effectiveness of the stun, with it being least effective when the electrodes were applied in a position that was not spanning the brain, but the amount of wool did not have any significant impact (P>0.05). In Abattoir A, the electrode position was found to have a significant impact (P<0.01) on the root mean square (RMS) voltage and the impedance, with them being the lowest when the electrodes were applied in the optimum position, but the amount of wool did not have any significant impact (P>0.05) on any of the electrical parameters in any of the abattoirs.

Overall, the study highlights the importance of electrode position for assuring effective stunning.