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Death inside gas chambers Every year over 300,000 minks are killed on  fur farms in Spain. Asphyxiated in gas boxes, their end is as tragic as their lives.

Most of the minks raised on fur farms are killed each year between  November and December. However, males used for breeding, and females who have not mated, are killed in March. Their bodies will be frozen until winter, when they will be skinned. Given the need for farmers to kill  animals on a massive scale, the most common method used is suffocation, due to the inhalation of carbon monoxide (CO) or carbon  dioxide (CO2), either individually or in groups. Section 8 of the report, The Welfare of Animals Kept for Fur Production [1], states: "All killing methods involve moving progressively along a shed, removing selected

Killing box used to asphyxiate the minks with exhaust gases from a tractor or feeding machine.

animals from their cages. As with weaning etc., this  usually causes both handled and nonhandled mink to vocalize, and at least in

«All killing methods involve moving

nervous strains is probably a source of short-

progressively along a shed, removing

term stress to  both the euthanised mink and

selected animals from their cages. As

their unpelted shed-mates. Where a gaseous

with weaning etc., this usually causes

euthanising method is used, the chamber/cart

both handled and non-handled mink to

itself may also be a source of disturbance."

vocalize, and at least in nervous strains is probably a source of short-

When mink are killed by gas in a killing box, 30

term stress to both the euthanised

- 50 animals may be placed in there, depending

mink and their unpelted shed- mates.»

on box-size (DAFF 2007). Unless

The Welfare of Animals Kept for Fur

unconsciousness is instantaneous, the

Production. Report of the Scientific

overcrowding and subsequent suffocation is

Committee on Animal Health and Animal Welfare [11].

likely to be an extremely stressful experience for the minks. Due to the sheer number of animals crammed inside the killing box, humidity and other factors, the carbon  monoxide or carbon dioxide gas is not distributed uniformly  inside. Workers from fur farms state that it is common practice to skin fully conscious minks, as they have not died during the gassing process. The use of gas in killing boxes is additionally problematic because of the minks' natural semiaquatic lifestyle. These animals have specific adaptations for  swimming and diving and, therefore, the ability to hold their breath for longer periods of time than terrestrial animals. Minks also detect, and respond to the effects of, hypoxia (low levels of O2 in blood) [2]. They show strong escape behaviours [3] when exposed  to gases. Researchers, Stephenson, Butler, Dunstone, and Woakes reported

«When animals are stuck into the box

a  marked bradycardia in minks during a dive

and forced to inhale the gases of

and concluded it was the result of physiological

combustion they move nerve-cisely,

adaptations to conserve oxygen [4]. They also

they become extremely excited and

 reported a fear-induced bradycardia.

have convulsions during 12 seconds. These convulsions begin 23 seconds

Carbon monoxide is a highly toxic gas that

after putting the animals in the

replaces oxygen in the  blood hemoglobin,


reducing the transport of oxygen throughout the

Lambooy, E., Roelofs, J.A., Van Voorst, N.

body  and causing the resulting lack of oxygen.

(1985). Euthanasia of mink with carbon

Another effect is the expansion of blood vessels


which causes bleeding. At high concentrations, the  animal loses consciousness, and suffers muscle spasms and cramps as a result  of the activity in the motor center of the brain that is stimulated by the carbon  monoxide. Partial paralysis occurs as a result of bleeding in the brain [5]. When high concentrations of carbon monoxide are used,  minks collapse after approximately one minute. The respiratory system stops working  after approximately two minutes and after approximately 5 to 7 minutes, the heart stops beating. Carbon dioxide is a gas that forms H2CO2 acid when combined with fluids of the respiratory system. This acid is highly irritating and causes great discomfort. Pulmonary edema and bleeding in the lungs [6] take place prior to loss of consciousness, regardless of whether only carbon dioxide or a mixture of carbon dioxide and oxygen is used. Several  scientific studies have demonstrated the high rejection that mink «No stress is as severe as the feeling

have of CO2 [3,7,8]. Avoidance studies have

of not being able to breathe. This

provided evidence to suggest  that animals

feeling of suffocation is not only the

unable to escape from an environment

result of the lack of oxygen but also

containing carbon  dioxide, experience stress

the inability to expel carbon dioxide.

and pain before the loss of  consciousness

Carbon dioxide drives breathing.

[14,15,16,17]. CO2, as well as CO replaces

Even after unconsciousness occurs,

oxygen in hemoglobin [5].

there should be a time when the animal feels it is choking..»

Research has demonstrated that a wide range

Dr. Bernard Rollin, Colorado University.

of species find concentrations of  more than 30% of carbon dioxide extremely unpleasant. They become noticeably distressed and exhibit escape behaviours [3,9,7,8,10,11]. Experiments using 70% carbon dioxide  have revealed that minks take at least 15 minutes to lose consciousness [12]. In Spain it is legal and habitual to use exhaust gases from a tractor or  feeding machine on mink farms. Due to the heat of the exhaust gases and the presence of  pollutants, filtered exhaust gases induce unconsciousness more slowly  than pure CO, and it is preceded by excitation and convulsions. Lambooy  (1984) observed the behaviour of minks killed using combustion gases as  carried out on farms [18]:  "When animals are stuck in the box and forced to inhale the combustion  gases, they become extremely excited and have seizures during 12 (+/- 6) seconds. These seizures begin at 23 (+/- 5) seconds after placing the  animals in the box." The European Food Safety Authority dissociates itself from the use of carbon monoxide  and carbon dioxide as a method of killing, and the European Commission also discourages the use of carbon dioxide [13]. Dutch law prohibits any such use of carbon  dioxide. A report by the EC Working Party on Animals in Laboratories  does not recommend the use of carbon dioxide and carbon monoxide for carnivores, because of the stress it causes.

Photos (from left to right and top to bottom): 1) Operator forcibly removing a mink.

4) Operators removing dead minks from the box.

2) Throwing a mink violently into the box.

5) Operator loading a trailer with the corpses.

3) Opening the gas valve to sphyxiate the

6) Warehouse where the dead minks are kept.


References 1. The Welfare of Animals Kept for Fur Production. Report of the Scientific Committee on Animal Health and Animal Welfare. out67_en.pdf 2. RAJ, M., MASON, G. 1999. Reaction of farmed mink (Mustela vison) to argon-induced hypoxia. Veterinary Record 145: 736 - 737. 3. COOPER, J., MASON, G.J., RAJ, M. 1998. Determination of the aversion of farmed mink ( Mustela vison) to carbon dioxide. Veterinary Record 143: 359-361. 4. STEPHENSON, R., PJ BUTLER, N DUNSTONE, and AJ WOAKES. 1988 Heart rate and gas exchange in freely diving American mink (Mustela vison) Journal of Experimental Biology 134: 435-442. 5. KENT, C. 1998. Basics of toxicology. John Wiley & Sons, Inc. 6. REVIEW OF COUNCIL DIRECTIVE 93/119/EC. 2008. On the protection of animals at the time of slaughter or killing. Respect for animals and Humane society international (UK). 7. RAJ, A.B.M. 1996. Aversion reactions of turkeys to argon, carbon dioxide, and a mixture of carbon dioxide and argon. Veterinary record 138: 592-593. 8. RAJ, A.B.M., GREGORY, N.G. 1995. Welfare implications of the gas stunning of pigs 1: Determination of aversion to the initial inhalation of carbon dioxide or argon. Animal welfare 4: 273- 280. 9. RAJ, A.B.M., GREGORY, N.G. 1991. Preferential feeding-behavior of hens in different gaseous atmospheres. British Poultry Science 32: 57. 10.RAJ, A.B.M., GREGORY, N.G. 1996. Welfare implications of the gas stunning of pigs 2: Stress induction of anaesthesia. Animal welfare 5: 71-78. 11.SIMONSEN, H.B., THORDAL-CHRISTENSEN, A., OCKENS, N. 1981. Carbon monoxide and carbon dioxide euthanasia of cats: duration and animal behaviour. British veterinary journal 137: 274. 12.HANSEN, N.E. ET AL. 1991. Euthanasia of mink (Mustela vison) by means of carbon dioxide (CO2), carbon monoxide (CO) and nitrogen (N2). British veterinary journal 147: 140-146. 13.EFSA. 2005. Aspects of the biology and welfare of animals used for experimental and other scientific purposes. Annex to the EFSA journal 292: 1-136. 14.AMBROSE, N., WADHAM, J. and MORTON, D. 2000. In: Refinement of Euthanasia. Progress in the Reduction, Refinement and Replacement of Animal Experimentation (M Balls, AM van Zeller, ME Halder, eds). Amsterdam: Elsevier

15.LEACH, M. C., BOWELL, V. A. ALLAN, T. F. and MORTON, D.B,. 2002a. Degrees of aversion shown by rats and mice to different concentrations of inhalation anaesthetics. Veterinary Record, 150: 606-815. 16.LEACH, M. C., BOWELL, V. A. ALLAN, T. F. and MORTON, D.B., 2002b. Aversion to gaseous euthanasia agents in rats and mice. Comparative Medicine, 52: 249-257. 17.LEACH, M. C., BOWELL, V. A. ALLAN, T. F. and MORTON, D.B., 2004. Measurement of aversion to determine humane methods of anaesthesia and killing. Animal Welfare, 13: S77-S86. 18.LAMBOOY, E., ROELOFS, J.A., VAN VOORST, N. 1985. Euthanasia of mink with carbon monoxide. Veterinary Record 116: 416.

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