Culling is probably the most important part of being a top notch canary breeder and by far is the most difficult part of breeding. This is also probably the most difficult topic to talk about. You probably won't see this topic on any other canary web site! Before getting into breeding canaries you should seriously consider this part of the hobby - can you do it? Culling is the process of destroying deformed birds. I was exposed to this early as my first baby canary was deformed. The first bird that I had raised had something wrong with its legs. At first, being a novice breeder, I thought it was normal. But it was soon apparent that something was wrong. The bird couldn't stand up or perch. After it matured it was able to 'hover' over a perch but just couldn't stand. The bird would just scoot across the bottom of the cage. The bird would get covered in feces despite the relatively clean grating on the bottom. It was a terrible sight. We nicknamed the bird scooter. Now that it had a name and was our first baby canary how could we destroy it? It wasn't until I had about 30 birds when we realized that we couldn't sell the defective birds and for sure we couldn't breed them. If you don't cull you will soon realize that all your cages will become full of defective birds and your breeding will come to an abrupt halt.

Deformities in Canaries
It seems that deformities in canaries are very common. This can be a good thing as genetic mutations are responsible for all of the different types of canaries we have today. Before you cull that bird consider the defect - do you have a new breed of canary? However, most defects are not beneficial. The most usual deformity is having a toe on the foot grow straight up in front of it. I see it most often at the pet stores and some birds will have them on both feet. This is a tough call for culling since the bird is otherwise healthy. Another is a defect in the eye, being blind in one or the other. I have not had this problem but know of a breeder who claims that it shows up quite often. If you have defects in your young consider buying new breeding pairs and selling the offending parents. (Sell them as pets, not breeders!)

How to cull
Once you decide you need to put down a bird, how do you do it? According to the Colorado Department of Agriculture Breeder Rules and Regulations it is stated, "Sick, diseased or injured birds shall be provided with veterinary care or disposed of IN A HUMANE MANNER, pursuant to § 35- 80-102(7)". What is a humane manner of disposal? The Colorado Department of Agriculture follows the guidelines put out by the American Veterinary Medical Association.

The Following Methods Are Not Acceptable!
(AVMA Guidelines)

Air embolism (injecting air)
Air embolism may be accompanied by convulsions, opisthotonos, and vocalization. If used, it should be done only in anesthetized animals.
Blow to the head
Unacceptable for most species.
Burning
Chemical or thermal burning of an animal is not an acceptable method of euthanasia.
Chloral hydrate
Unacceptable in dogs, cats, and small mammals.
Chloroform
Chloroform is a known hepatotoxin and suspected carcinogen and, therefore, is extremely hazardous to personnel.
Cyanide
Cyanide poses an extreme danger to personnel and the manner of death is aesthetically objectionable.
Decompression
Decompression is unacceptable for euthanasia because of numerous disadvantages.
(1) Many chambers are designed to produce decompression at a rate 15 to 60 times faster than that recommended as optimum for animals, resulting in pain and distress attributable to expanding gases trapped in body cavities.
(2) Immature animals are tolerant of hypoxia, and longer periods of decompression are required before respiration ceases.
(3) Accidental recompression, with recovery of injured animals, can occur.
(4) Bleeding, vomiting, convulsions, urination, and defecation, which are aesthetically unpleasant, may develop in unconscious animals.
Drowning
Drowning is not a means of euthanasia and is inhumane.
Exsanguination (to drain of blood)
Because of the anxiety associated with extreme hypovolemia, exsanguination should be done only in sedated, stunned, or anesthetized animals.
Formalin
Direct immersion of an animal into formalin, as a means of euthanasia, is inhumane.
Household
Products and solvents Acetone, quaternary compounds (including CCl4 ), laxatives, clove oil, dimethylketone, quaternary ammonium products*, antacids, and other commercial and household products or solvents are not acceptable agents for euthanasia.
Hypothermia
Hypothermia is not an appropriate method of euthanasia.
Neuromuscular blocking agents
When used alone, these drugs all cause respiratory arrest before loss of consciousness (nicotine, magnesium sulfate, potassium chloride, all curariform agents) so the animal may perceive pain and distress after it is immobilized.
Rapid freezing
Rapid freezing as a sole means of euthanasia is not considered to be humane. If used, animals should be anesthetized prior to freezing.
Strychnine
Strychnine causes violent convulsions and painful muscle contractions.
Stunning
Stunning may render an animal unconscious, but it is not a method of euthanasia (except for neonatal animals with thin craniums). If used, it must be immediately followed by a method that ensures death.
Tricaine methane sulfonate (TMS, MS 222)
Should not be used for euthanasia of animals intended as food.

Recommended Methods
(AVMA Guidelines)

Carbon Dioxide
Carbon dioxide is recommended by most animal rights activist groups and used by human societies around the world. CO₂ is inexpensive but you have to make or buy a Euthanasia Chamber and have a way to fill the chamber with the gas. Other advantages: The rapid depressant, analgesic, and anesthetic effects of CO₂ are well established. Carbon dioxide is readily available and can be purchased in compressed gas cylinders. Carbon dioxide is inexpensive, nonflammable, nonexplosive, and poses minimal hazard to personnel when used with properly designed equipment. This gas causes very little distress to the birds. A CO₂ concentration of 60% to 70% with a 5-minute exposure time appears to be optimal. This method is recommended provided that the gas comes from a pressurized cylinder and not a chemical reaction or internal combustion engine exhaust.
Carbon Monoxide
Same as carbon dioxide only much more dangerous for the user. This gas is colorless and odorless and builds up in your system binding to hemoglobin and replacing oxygen in your blood. You can poison yourself as well as the birds if you don't have a proper setup. Use only with the proper setup and then with extreme caution.
Inhalent Anesthetics
Highly effective providing you dose correctly. Recommendations — In order of preference, halothane, enflurane, isoflurane, sevoflurane, methoxyflurane, and desflurane, with or without nitrous oxide. I have not found any of these compounds for sale without regulations. They may be difficult to obtain and can be rather expensive.
Nitrogen or Argon
These two inert gasses are relatively safe to use (non toxic in low concentrations). Using either of these two gasses can be stressful to the birds unless the chamber is filled quickly and has less than 2% oxygen. Birds should be sedated first. Although N₂ and Ar are effective, other methods of euthanasia are preferable.
Gunshot
Dangerous but effective. Should have a consistent technique.
Decapitation
Quick but messy.
Barbituates
Intravenous injection is necessary for best results and requires trained personnel.

In conclusion, the best way to euthanize is to use Carbon Dioxide and a chamber.