Waterbath stunning in slaughterhouses is a common practice in the EU. To what extent various waveform and frequency combinations of AC and DC stunners influences the effectiveness of this method, was investigated. Males and females seem to react differently.
By Dr. Roel Mulder, Spelderholt Poultry Consulting & Research Epe, the Netherlands
Food animal products such as meat, eggs and milk, are consumer favourites, although others prefer a form of vegetarianism, or even veganism, as part of their lifestyle. For the latter groups, one of the reasons is the general regard about using animals to benefit humans. Also, the way that animals are treated at the time of slaughter is a matter of concern.
In the European Union, animals must be rendered unconscious before slaughter and incapable of perceiving pain. An effective stunning method therefore needs to be applied. Details are in EU directive 93/119/EC.
By definition, stunning must permit the bird to recover consciousness, so stunned broilers should recover consciousness and be able to regain the ability to maintain an erect posture within 120 seconds. At present, electrical waterbath stunning is the most common method used in commercial slaughterhouses. After shackling, the birds’ heads are immersed into an electrified waterbath, causing the current to run through the head and body and thus inducing unconsciousness. Stunning and bleeding are integral steps in the slaughter of poultry and should be evaluated together.
Stunning facilitates automated processing. For processors an additional advantage of applying this method is that operating costs and space requirements are low. Depending on the electrical setup the animals can be stunned to kill, thus preventing recovery of the birds during bleeding. Cardiac arrest stunning has, on the other hand, been associated with meat quality defects due to convulsions. Poultry subjected to electrocution or gas stunning protocols are characterised as stun-kill because birds will not regain consciousness.
Stunning effectiveness assessed
In a PhD Thesis, Simone Prinz, Nijmegen University, the Netherlands, reported on her studies on “Waterbath stunning of chickens” and more specifically on the “Effects of electrical parameters on the electroencephalogram and physical reflexes of broilers”. A wide range of electrical setups applied in an electrical waterbath were tested under equal experimental conditions. Systematically parameters as waveform, frequency and current level and their interrelation were tested. The effectiveness of the Simmons stunner, a two-step waterbath stunner, which uses a saline solution to wet feathers and skin for better conductivity, was analysed in comparison with the high voltage stunning in the EU. Stunning effectiveness was assessed using EEG analysis and evaluation of physical reflexes. Therefore, a non-invasive device for recording brain waves was developed and validated. A special feature in these studies was that all aspects were analysed for male and female broilers separately. Unfortunately in this study the effects on meat quality were not assessed, but will be included in future studies.
A variety of waveform and frequency combinations were used to achieve good stunning results, and comparable results with regard to inducing unconsciousness of the birds were obtained with AC and DC stunners. The maximum acceptable frequency at 150 mA was 400 Hz. The studies showed that due to higher resistance, females obtain a lower current than males in constant voltage stunners, resulting in lower stunning effectiveness. Constant current stunners could solve this problem.
Stronger rules expected
A proposal improving animal treatment at time of slaughter was recently adopted in the EU. The idea is that existing legislation has to be simplified and brought more in line with food hygiene regulations. The proposal integrates animal welfare aspects into the design of slaughterhouses and requires regular monitoring of the efficiency of stunning techniques. Beginning in 2013, stunning and killing criteria for slaughterhouses will be updated and the general parameters for using electricity to render the animal unconscious, or gas for birds, more concretely defined. This means that carbon dioxide and waterbath stunners, for example, will still be permitted, but their use may be restricted. Slaughterhouses have to appoint a specific person for animal welfare and ensure that those working in the facility are properly trained and certified. Requiring standardised procedures for animal welfare is an innovation of this regulation, which will require operators to evaluate the efficiency of their stunning methods through animal-based indicators. After stunning, animals will have to be regularly monitored to ensure they do not regain consciousness before slaughter. Additionally, manufacturers of stunning equipment will have to provide instructions for ensuring proper animal welfare.
Recently in the Netherlands, the Minister of Agriculture, Nature Management and Food posed a future ban on the use of waterbath stunning after the publication of very negative results in a survey in poultry slaughterhouses on the adequate application of the conditions set in the EU directive on the use of this method. In light of the recent EU measures it has to be seen under which conditions waterbath stunning will be permitted in the future.