In a training exercise to test contingency plans in the event of an outbreak of bird flu here, 12,000 chickens were gassed at a farm in Kilmeedy, Co Limerick, yesterday.
The exercise, organised by the Department of Agriculture and Food, was conducted without fire brigade officers, who have been complaining that they do not have proper equipment to take part in such exercises.
Although the gassing of the birds by carbon dioxide took only 10 minutes and was described as a "humane process", the use of the CO2 drew criticism from Compassion in World Farming - Ireland.
The group's director, Mary-Anne Bartlett, said that while the use of carbon dioxide was permissible under the world organisation for animal health's (OIE) standards, the department should have used inert gases such as argon, which were non aversive.
This, she said, was because carbon dioxide is an aversive gas and can cause suffering while they birds are dying.
Yesterday's exercise, the second to have taken place in the State in the past few months and the fourth to have taken place on the island, saw 11,600 broiler hens and 400 cocks, which had reached the end of their working lives, killed.
TV monitors were installed so 25 veterinary and 35 other staff observing the event could monitor the reaction of the chickens from outside.
Pat Mescall, superintendent veterinary inspector with the Department of Agriculture in Limerick, said the training exercise was "very successful" and that department staff were now in a much better position to deal with any possible outbreak of bird flu.
Mr Mescall said the poultry used in yesterday's exercise were chosen because they had reached the end of their productive lives. The dead chickens were being sent to a rendering plant where their carcasses will be burnt and converted into bone meal, he added. "None of these animals will end up in the human food chain," he added.
At no point was any member of staff inside the shed and the carbon dioxide used was pumped in from outside.
In a draft contingency farm, firemen should have been involved in going into the shed to check the building was clear of gas to allow the birds be removed. However, a spokesman for the department said that the company which supplied the gas had also provided the personnel and equipment for checking the premises.
The farm in question was chosen because there were no other animal sheds on the site and no dwelling house, according to the department.