Improvements in the design of waterbath stunners in poultry slaughterhouses can raise bird welfare and reduce carcass damage, a new study has found.
Research undertaken by the University of Bristol looked at the frequency of pre-stun shocks associated with the entry of birds into waterbaths, and the effect this had on carcass quality.
"If a bird's leading wing or any other part of the bird makes contact with the live water before the head, the bird will receive a potentially painful pre-stun shock," says the report. This can cause the birds to "fly the waterbath", meaning they are not stunned at all before reaching the automatic neck cutters - something which is against the law.
The researchers first studied the frequency of pre-stun shocks on Ross cockerels and pullets over a two-week period in a commercial plant.
They found there was a significantly higher incidence in pullets, with 9.8% showing repeated contractions due to pre-stun shocks, and 1.6% over-flying the whole length of the waterbath.
"When heavier birds are inverted and restrained on a shackle, they are physically unable to display much movement and are therefore less able to avoid a swift immersion in the waterbath," says the report. "Lighter, more active birds are much more likely to receive a pre-stun shock."
The problem was also greater for free-range birds compared with more sedentary broilers.
The study then looked for a correlation between pre-stun shocks and carcass quality, checking 500 birds for two consecutive days for broken bones and haemorrhages. It found that for both measures carcass and meat quality were "significantly and adversely affected" by the occurrence of pre-stun shocks, leading to extra trimming and downgrading.
These results suggest that there are strong commercial as well as welfare arguments for eliminating pre-stun shocks, says the report, "entirely justifying any financial output that would be required to improve controlled entry of birds into a waterbath stunner".
It suggests constructing an electrically isolated ramp over the entrance to the waterbath, to project the head into the live water more quickly.
* The research was published in the journal of the Universities Federation for Animal Welfare.
More on this topic:
Report on Better ways when it comes to stunning
Philip Clarke on G+