Animal Welfare Assessment of Turkey Euthanasia Methods

The concern for animal welfare is not restricted only to conditions in which animals are reared, but also covers how they are euthanized. Animal processing facilities have long adopted humane methods, but occasionally, on-farm euthanasia is necessary, and is thus also being explored. Scientists are concentrating on animal welfare and operator-related issues to choose euthanasia methods that are the fastest and least painful. 

Conventional On-Farm Euthanasia Needs Improvement

Farmers have to euthanize birds on-farm, when the poultry is unhealthy or incapacitated for various reasons. The task is not easy for the farmer, and the methods they use must be swift to ensure animal welfare.

There are a few recommended techniques that farmers can use, but the most used of these involve the manual application of force, such as in manual cervical dislocation. Heavy birds, like turkeys, pose additional challenges due to their weight and size, which can range from seven to twenty kilograms depending on their age.

Moreover, legislative restrictions by the European Union forbid the use of this technique in birds heavier than three kilos. In a recent survey, most turkey producers and veterinarians indicated that they prefer alternate means of euthanasia.

Besides addressing the problems of handling heavy turkey, the alternative techniques explored also needed to be quicker and have a higher rate of success. This study brings further specificity to previous studies on poultry euthanasia, focusing specifically on the most humane methods for individual, heavy turkeys.

Methods like electrocution and carbon dioxide inhalation have been used commercially in processing plants. These techniques are designed for large-scale euthanasia, and their effectiveness and suitability for individual turkeys is not known. Hence, tools for the application of these methods for euthanizing individual birds have yet to be developed.

Testing Four Alternative Methods

A team of poultry scientists—Jacobs, Bourassa, Boyal, Harris, Josselson, Campbell, Anderson, and Buhr—from various research institutes in the USA, tested adaptations of electrocution and carbon dioxide inhalation euthanasia methods on the farm. They compared them with two mechanical euthanasia methods that are currently used on farms: the Koechner Euthanizing Device (KED) and the Turkey Euthanasia Device (TED). KED, used for mechanical cervical dislocation, has a low kill success rate between 54-88%, while TED been more successful at 90-100%. 

This experiment was approved by Virginia Tech’s Institutional Animal Care and Use Committee (IACUC) and followed the standard operating protocol set by the “Euthanasia Methods Approved for Poultry.”

In total, 174 healthy, well-fed turkeys (hens and toms) were euthanized in three days. The birds were breeder turkeys at flock termination (38 weeks old) or 21-week-old market poultry. The four techniques were tried on each of the three days. Three operators, one with twenty years experience, and two with a year’s experience were involved.

Commercially available equipment was used for KED and TED. For the other two methods, the scientists developed portable tools.

The scientists developed a head CO2 inhalation device, where the gas administered reached 70% in a minute and exceeded this level in the next three minutes. A commercial head-only apparatus was also used. A commercial gas analyzer, the F-920 Check It! Gas Analyzer, was used to measure the levels of gas administered to the birds.

The gas analyzer, manufactured by Felix Instruments Applied Science, is made to check headspace gas accumulated in plastic packaging, so it was suitable to measure gas in the present design. The F-920 can make continuous mode measurements of CO2 from 0-100% with a resolution of 0.01%, and the recording time is less than six seconds.

The scientists used four operator-related and four animal welfare-related criteria to evaluate the tested techniques. Provided the operators were trained in all four techniques, the scientists concluded that the following criteria for operators were met:

• The technique was easy and manageable
• Successful when performed by a single person
• Successful at the first attempt
• Tools were portable within a farm   

The following animal welfare parameters were used:

• Loss of reflexes, such as nictitating membrane reflex, month gaping, and musculoskeletal movements
• Acute distress measured by elevated blood corticosterone (CORT)
• External damage, such as torn skin and blood loss
• Kill success

Checking Animal Welfare Parameters

Most of the results for the four methods did not differ between the three days the experiment was conducted.

Nictitating membrane (third eyelid) reflex was used to evaluate the loss of consciousness, mouth gaping measured cerebral cortex control, and musculoskeletal movements measured spinal cord death. The four techniques differed significantly in reflex losses in turkeys.

Loss of consciousness indicates that the bird can feel no pain. Using the loss of the nictitating membrane reflex as the criteria, the scientists concluded that the turkeys lost consciousness within fifteen seconds of application of euthanasia, in CO2, electric, and TED methods.

Nictitating membrane and mouth gaping reflex loss took the longest time in KED, compared to the other three methods.

Musculoskeletal movements loss, in general, was the last to cease; the time needed was similar in KED and TED and was more prolonged than in CO2 and electric methods.

Brain stem death occurred within fifteen seconds in CO2 and electric methods but took longer in TED and KED. Returning reflexes, which indicate the possibility of birds recovering, were also higher in KED (25 and 75%) and TED (23 and 47%), compared to no returning reflexes in CO2 and electric methods.

Latency, or the time-lapse between stimulus and a reflex response, was the least in CO2—around  eighty seconds—and movements stopped within fifteen seconds afte the application.

This is the first study to quantify CORT levels in turkeys to evaluate euthanizing methods but found no difference due to the technique used. The results differed over the three sampling days, due to the use of different collection methods. It was higher on the first day when the birds were crated, and the lowest on the third day, when they were held in the field. Moreover, differences in strains and age of birds could have also played a role.

Unsuccessful attempts are a major animal welfare concern and must be avoided. In terms of kill success, the KED method was the least successful, and the other three were comparable. However, the efficacy of the CO2 method could be established only after eight minutes (four minutes for application and a wait of four minutes before recording results); this was a matter of concern for the scientists in concluding the speed of the method. The success rate did not depend on the sex and age of the birds.

Figure 1. “Prevalence of successful and unsuccessful kills per euthanasia method (CO2, vent-to-mouth electrocution, mechanical cervical dislocation [KED], captive bolt [TED]) per sampling day (1, 2, and 3) (n = 12–17 per method per sampling day). Numbers within column represent absolute bird numbers,” Jacob et al. 2021. (Image credits: https://doi.org/10.1016/j.psj.2020.11.001)

In terms of external damage, there was no torn skin or blood loss after CO2 and the electric method. When the skin tore, there was blood loss; this happened in 100% of the cases in the TED application and 63% of cases in KED. Blood loss is considered a biohazard during disposal if the birds are contaminated by diseases.

Electric Method is Recommended

Considering the results of all the tests, the scientists concluded that the KED method was the slowest and had the lowest success rate. The electric method was considered the best method for heavy individual turkeys because it resulted in quick loss of consciousness and death, the lowest CORT levels, only one failure, and no external damage. The CO2 method was judged the second best, and TED was rated third. It is noteworthy that the CORT tests, which were conducted for the first time in euthanasia evaluation in this study, were one of the decisive factors in choosing the method, proving that measuring external features alone may not be enough.

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Vijayalaxmi Kinhal
Science Writer, CID Bio-Science
Ph.D. Ecology and Environmental Science, B.Sc Agriculture

Sources

Jacobs, L., Bourassa, D.V., Boyal, R. S., Harris, C.E., Josselson, L.N.B., Campbell, A., Anderson, G., R., & Buhr, J. (2021). Animal welfare assessment of on-farm euthanasia methods for individual, heavy turkeys. Poultry Science, 100 (3). https://doi.org/10.1016/j.psj.2020.11.001