Pre-stun shocks at the entrance to a waterbath

A bird’s head must always be the first part of its body to enter the electrified water. Any possibility for a part of a bird to come into contact with electrified water before the head is immersed, may result in a severely painful pre-stun electric shock.

Birds might be suffering from pre-stun shocks if, at the same point(s) on a shackle line, birds tend to suddenly exhibit abrupt behaviours that might indicate distress, eg flapping and/or high-pitch vocalisations. Also, if birds display more than one contraction on entry to the water, this may indicate interrupted application of the initial current flow.

Pre-stun shocks typically trigger an escape response in birds and therefore can cause them to flap vigorously and to lift up their heads, and sometimes their bodies, above the surface of the electrified water. As a result, birds may not be stunned immediately and may not receive an electric current for the minimum recommended duration; or they may not be stunned at all if they pass through the waterbath without making contact with the electrified water. Vigorous flapping may increase the likelihood of additional pre-stun shocks to the wings and the situation can therefore be cyclical. If neighbouring birds are hit by flapping wings they may be disturbed and begin flapping too.

Flapping birds may damage themselves, particularly if, in the panic, they beat their wings and hit their heads against the side panels of a waterbath. As well as being detrimental to bird welfare, pre-stun shocks are associated with damage to the carcass, eg red wing tips; haemorrhages in the wing, major fillets (dorsal and ventral aspects) and minor fillets (dorsal aspect); and broken pectoral bones.

Risk factors for pre-stun shocks:

• A bird’s wings are prone to receiving pre-stun shocks, particularly when the bird holds them open. In this position the carpometacarpus may be especially close to the water.
• The large wingspan of geese and turkeys puts them at particular risk of pre-stun shocks because their wings often hang below their head.
• Agitated, struggling birds may hold their wings open and some flap; as such the wings may be more likely to make contact with the electrified water.
• Sometimes birds’ legs and/or feet contact the earthed rubbing bar (eg when a shackle line descends just before the entrance to a waterbath). If the entry ramp is not electrically isolated or if electrified water overflows the entrance, such birds may receive pre-stun shocks.
• Pre-stun shocks may occur if a shackle line descends too gradually, as birds enter a waterbath. For example, when a bird’s beak touches the water current will begin to flow and the skeletal muscle in the body will contract, causing the bird to become rigid and typically arch its back (reflex dorsiflexion). This rigidity may effectively lift up the bird, including its head. If, within one second of the initial contact, the beak momentarily loses contact with the water, the bird may receive a pre-stun shock. Thereafter, even if the bird’s head regains contact with the water and becomes fully submerged, the earlier pre-stun shock may still have caused suffering.

If pre-stun shocks are suspected to occur, personnel must notify the AWO and/or veterinarian and there must be an investigation to identify the extent of the problem and the necessary corrective action, which may require redesigning the entrance to the waterbath, or perhaps the entire shackle line.

Next: Minimising pre-stun shocks