A report of a study into the incidence and effect of pre-stun shocks in a commercial broiler processing plant using an electrical waterbath stunning system, the most commonly used system in the UK, has been published in Animal Welfare, the journal of the Universities Federation for Animal Welfare(UFAW).

The research was undertaken by Professor Toby Knowles and Steve Wotton from the University of Bristol's School of Veterinary Sciences and Muhammad Asif  Rao, and was supported by a Dorothy Sidley Memorial Scholarship from the Humane Slaughter Association (HSA).

The study identified a significant level of pre-stun shocks, particularly in lighter, more active birds, correlated with a significant level of adverse effect on carcase and meat quality. Pre-stun shocks were also seen to be a contributor to the incidence of mis-stuns (by causing birds to ‘fly’ the waterbath).

The results of the study indicate not only a serious welfare problem but also a significant financial burden for producers of broiler chickens stunned using the electrical waterbath.

The report states “EC Regulation (1099/2009) stipulates…that for electrical waterbath stunning a key consideration is the prevention of electrical shocks before stunning. The results reported here add very strong commercial and economic arguments to this legislative welfare requirement, entirely justifying any financial output that would be required to improve controlled entry of birds into a waterbath stunner…(pre-stun shocks) can be prevented by careful waterbath entry design and modification. It should be entirely possible to avoid (pre-stun shocks) in commercial processing plants and there is a strong economic reason to do so.”

Paper: The effect of pre-stun shocks in electrical water-bath stunners on carcase and meat quality in broilers, MA Rao, TG  Knowles and SB Wotton, Animal Welfare, Volume 22 Issue 1 February 2013.