Electrical water bath stunning is the most common pre-slaughter method for broiler chickens, but its effectiveness is variable, and alternative systems including CAS offer more consistent insensibility.
Pre-slaughter stunning is a welfare intervention that ranges from moderately effective to highly effective depending on the method and its implementation. Water bath stunning requires conscious birds to be shackled and inverted — generating acute distress before stunning — and may fail to render all birds fully insensible. Controlled atmosphere systems that expose birds to high CO2 or inert gases before handling avoid the shackling stress and achieve more consistent insensibility, but CO2 exposure is aversive in some protocols. Inert gas CAS systems (argon, nitrogen) offer the best welfare profile by avoiding both shackling consciousness and CO2 aversion. Regulatory requirements in the EU are moving toward CAS adoption.