Gas alternatives to carbon dioxide for euthanasia: A piglet perspective

Published in Animal Science at December 2, 2014. By: J.-L. Rault, K. McMunn, J. Marchant-Forde, D. Lay. Gas alternatives to carbon dioxide for euthanasia: A piglet perspective. ARS-USDA.


A humane, practical, economical and socially accepted euthanasia method.

The use of nitrous oxide as an anesthetic/euthanasia agent may prove to be affordable, feasible and more humane than other alternatives.
The neonatal stage is a critical time in the life of a pig, when they are prone to become sick or weak. This is the stage at which most euthanasia procedures are required if the pig is judged unable to recover. Any euthanasia method should be humane, practical, economical and socially acceptable to be universally accepted.

How is the research setup?

This research sought to: 1) identify a method of scientifically determining if piglets find a gas aversive, using an approach-avoidance test which relies on the piglet’s own perspective (Experiments 1 and 2), and 2) test different gas mixtures to determine if they are effective and humane for neonatal piglet euthanasia, using a two-step anesthesia-euthanasia procedure (Experiment 3). The investigators hypothesized that nitrous oxide, and alternatively argon and nitrogen, were less aversive than carbon dioxide and would induce anesthesia prior to using carbon dioxide to complete the euthanasia procedure.

Pigs were allowed to walk freely between one chamber filled with air and another chamber either gradually filled with gas (Experiment 1) or pre-filled with gas (Experiment 2). Experiment 1 tested carbon dioxide, CO2 (90%) and air (10%); nitrous oxide, N2O (60%) and CO2 (30%); argon, Ar (60%) and CO2 (30%); and nitrogen, N2 (60%) and CO2 (30%).

Since piglets had to be removed when they became panicked, the test was shortest (P < 0.01) for the pigs in the CO2 treatment compared to pigs in the N2O/CO2, Ar/CO2, and N2/CO2 treatments, 3.1 ± 0.2, 8.5 ± 0.6, 9.6 ± 0.4, and 9.9 ± 0.1 min, respectively. Nonetheless, all gas mixtures adversely affected the pigs, causing the pigs to leave the test chamber. In Experiment 2, piglets were allowed to enter a chamber pre-filled with N2/CO2 or N2O/CO2 (both 60%/30%). Pigs exposed to the pre-fill chambers entered a state of panic in less than 20 s, much faster in comparison to the gradual fill method, which support than this method was more aversive.

In Experiment 3, piglets were euthanized using a 2-step procedure. Pigs were first placed in a gradual fill chamber with 1 of 4 gas mixtures: 90% CO2, N2/CO2, N2O/CO2 or N2O/O2 (the last three mixtures at 60%/30%) followed by placement into a 90% CO2 pre-fill chamber when the pigs became panicked or were anesthetized. All three gas treatments that contained CO2 killed pigs more quickly than N2O/O2 (P < 0.05). However, N2O/O2 was the only treatment that anesthetized the pigs instead of causing squeals or panic, although requiring about 12 min longer. Although longer, a 2-step procedure in which pigs are anesthetized with a mixture of N2O and O2 prior to being euthanized by immersion in CO2 may prove to be more humane than CO2 alone.

The results

They found that nitrous oxide in oxygen appeared to be less aversive than nitrous oxide, nitrogen, or argon all combined with low (30%) concentrations of carbon dioxide or 90% carbon dioxide by itself. This study is the first to investigate the use of nitrous oxide at sufficiently high concentrations to cause anesthesia.

Nitrous oxide, commonly referred to as laughing gas, has been widely used in human surgery and dental offices for its pain-relieving, sedative and anxiolytic effects. It is cheap, non-flammable, non-explosive, legally accessible and not classified as a drug in the U.S., and already commonly used in the food industry as a propellant for food products. Development of its use into an automated procedure will allow producers to implement it with little effort. Thus its use as an anesthetic/euthanasia agent may prove to be affordable, feasible and more humane than other alternatives.


Experts urge action after H7N9 shows Tamiflu resistance

South China Morning Post, March 1, 2017. Experts said signs of resistance in a new strain of the deadly H7N9 bird flu virus against a drug used to treat people with the infection needs swift investigation to clarify how to handle the mutation.


Tamiflu resistance

Two patients in Guangdong province with a new and more virulent strain of the virus have shown signs of failing to respond to the drug Tamiflu, the Nanfang Daily reported this week, citing Zhong Nanhsan, an expert in respiratory diseases.
Virologists said the finding did not mean the drug was ineffective against bird flu, but a swift investigation was needed to assess how to handle the situation. There have been over 1,200 laboratory confirmed cases of human infection for bird flu in mainland China since the first was reported in 2013.
As of Sunday, 94 people have died from the illness on the mainland this year. The number of deaths so far this year have already surpassed the total number of H7N9 fatalities last year, which was 73.
Mutation of H7N9 bird flu strain found in Guangdong patients

The drug resistance was found in two patients found to have the mutation of the virus, the report said. The new strain was identified by the China Centre for Disease Control.
Taiwan’s Centre for Disease Control announced earlier this month that gene sequence analysis of a H7N9 bird flu patient, who fell ill after visiting Guangdong, found the virus had a mutation that was resistant to antiviral drugs such as Tamiflu and Relenza. The patient, a 69-year-old businessman, died earlier this week.

Zhong was quoted in the Nanfang Daily as saying most patients on the mainland were responding to Tamiflu treatment, suggesting the mutated strain of H7N9 was not the dominant virus, or “a considerable amount of viruses” did not mutate.

He Jianfeng, chief expert in infectious diseases at the Guangdong Provincial Centre for Disease Control and Prevention, told the newspaper both patients with the new strain had taken Tamiflu before and it was not clear whether the drug resistance was caused by previous use of the treatment or the virus mutation.
Professor Malik Peiris, a virologist at the University of Hong Kong who published a paper in the medical journal The Lancet four years ago saying H7N9 patients in Shanghai had previously shown antiviral resistance, said Tamiflu resistance occurred occasionally in bird flu patients treated with the drug before.

China’s H7N9 bird flu measures came too late, experts say

His further work showed these patients can be treated with alternative antiviral drugs. Professor Peiris called for a quick investigation into the latest H7N9 virus mutation.
“We need more information on how widespread this resistance is in recent viruses, especially those with the high pathogenic mutation,” he said.

Tamiflu can still be useful for treatment and early use of the drug will reduce the chance of resistance developing and increase the chance of a cure, he added. Patients who have begun antiviral treatment need to be monitored to see whether there was a good response and to change to alternative drugs if there was no improvement, he said.