Development of a microwave energy delivery system for reversible stunning of cattle

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Highlights

  • Application of microwave energy may be a future method of rendering cattle insensible prior to slaughter.

  • Cadaver studies demonstrated that target temperatures can be achieved to induce unconsciousness.

  • The unconsciousness is potentially reversible.

Abstract

Stunning prior to slaughter is commonly used to render the animal insensible to pain. However, for certain markets, stunning is disallowed, unless the animal can fully recover if not slaughtered. There are very few available methods of inducing a fully recoverable stun. This paper describes the development of a microwave energy application system for stunning cattle. Cadaver heads were used to demonstrate that brain temperature could be raised to a point at which insensibility would be expected to occur (44 °C), and to calculate the power and time combinations required to achieve this in a range of cattle weights. Surface heating was identified as a cause for potential concern, which was mitigated by the development of another type of microwave applicator.

Although the applicator and process variables require validation in animal studies, this technology shows promise as a method of inducing a recoverable stun.

Introduction

The prevention of unnecessary suffering at slaughter is considered to be imperative for the “right to operate” for the meat industry, and as such, the majority of slaughtered animals are stunned prior to slaughter by mechanical, electrical or gas inhalation means. However, the Jewish and Muslim religious texts require animals to be ‘whole and undamaged’ at the point of slaughter (exsanguination), which leads to these animals being slaughtered without prior stunning. Where stunning has been permitted by these communities, they require that any such stun is fully reversible in order to meet the requirements of their religious laws.

Commonly used stunning methods such as mechanical captive bolt stunning cannot be used when processing animals for these markets, as these methods are non-recoverable. Head only electrical stunning is a recoverable stun used in sheep slaughter, but is not widely used in cattle due to concerns over the duration of stun (Lambooy and Spanjaard, 1982, Wotton et al., 2000). Therefore, there is a need to investigate alternative reversible methods of stunning.

A microwave-generated dielectric stun system, which produces an electromagnetic field within the brain, raising the brain temperature to the point at which insensibility occurs, has been developed and patented (PCT/AU2011/000527) (Ralph et al., 2011). Initial development work on sheep demonstrated that the brain temperature in cadaver heads could be selectively raised by 10 °C in less than 1 s. Further trials using anesthetized sheep confirmed that brain temperature could be raised to above 43 °C, and this resulted in an electroencephalogram (EEG) trace indicative of seizure-like activity (Small et al., 2013). Similarly, Rault et al. (2014) demonstrated that application of microwave energy to the brains of anesthetized cattle resulted in EEG traces indicative of seizure-like activity, which is considered to be incompatible with consciousness. These preliminary studies suggest that microwave energy application could be a suitable method of inducing a fully reversible stun, which may meet the requirements of those Jewish and Muslim markets that allow pre-slaughter stunning.

The current paper describes the further development of this technology towards providing a reversible stun system for cattle.

Section snippets

Prediction of efficacy

The dielectric properties of any material are the main parameters that influence how microwave energy is coupled into the material and how efficiently this energy is then converted into thermal energy. These properties are described by the following complex equation:ε=ε+jε

The real part of the equation (ε′), the dielectric constant, represents the ability of the material to store energy when a microwave field is applied. The imaginary part of the equation (ε″), the loss factor, determines how

Prediction of efficacy

Utilising the dielectric properties of tissue as published by Boon and Kok (1988), it was predicted that 11.3% of incident energy would be absorbed by the skin and 2.9% by the bone, resulting in a depth of penetration into the brain of 30.2 mm. The dielectric properties given by Gandhi et al. (1996) suggested that 6.0% and 11/3% of incident energy would be absorbed by the skin and bone respectively, leading to a depth of penetration of 27.7 mm.

Temperature profiling

Data from the first eight heads treated indicated

Discussion

In developing a dielectric stunning system, the main area of concern is the penetration depth into the brain. To estimate this, the expected approximate percentage of incident power absorbed into the skin and bone was calculated based on approximate thicknesses and the assumption that power travels perpendicular to the plane of each material. For 922 MHz, predicted depth of penetration into cattle brain was estimated to be between 27.7 and 30.2 mm, and this was supported by testing using cadaver

Conclusions

Application of microwave energy has the potential to induce insensibility in cattle, because it causes rapid increases in cadaver brain temperature to a point above which insensibility would be expected to occur (43 °C).

Conflict of interest

This study describes part of the work leading to Patent PCT/AU2011/000527.

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