Chick sexing is the method of distinguishing the sex of chicken and other hatchlings, usually by a trained person called a chick sexer or chicken sexer. Chicken sexing is practiced mostly by large commercial hatcheries to separate female chicks or hens (destined to lay eggs for commercial sale) from the males or cocks (most of which are killed within days of hatching because they are irrelevant to egg production). The females and a limited number of males kept for meat production are then put on different feeding programs appropriate for their commercial roles.
Different segments of the poultry industry sex chickens for various reasons. In farms that produce eggs, males are unwanted; for meat production, separate male and female lines for breeding are maintained to produce the hybrid birds that are sold for the table, and chicks of the wrong sex in either line are unwanted. Chicks of an unwanted sex are killed almost immediately to reduce costs to the breeder.
Methods of chick sexing
Vent sexing, also known simply as venting, involves squeezing the feces out of the chick, which opens up the chick's anal vent (called a cloaca) slightly, allowing the chicken sexer to see if the chick has a small "bump", which would indicate that the chick is a male. Some females also have bumps, though they are rarely as large as those of male chicks.
The eminence or genital organ is found midway on the lower rim of the vent, and looks like a very small pimple. Most males have a relatively prominent eminence, most females have none. However, a small proportion of both males and female have relatively small eminences. Sexing these chickens can be quite difficult, but with regular practice the sexer will eventually learn to identify the differences.
When learning to sex chickens it is best to assume that chickens with small eminences are female. The male eminence is solid and will not disappear upon gentle rubbing with your thumb.
A paper about vent sexing was published in Japan in 1933 by Professors Masui and Hashimoto, which was soon translated into English under the title sexing baby chicks. After their discovery, interested poultry breeders hired those who had been trained in Masui and Hashimoto's technique, or sent representatives to Japan to learn it. 
(See also Delayed feathering in chickens)
In 1969, after three years of genetic research, Tegels Poultry Breeding Company developed broiler chickens that could be feather-sexed. The result was a strain that would produce slow-feathering males and fast-feathering females.
In the slow-feathering males the coverts are either the same length or longer than the primary wing feathers. In the fast-feathering females, the primary wing feathers are longer than the coverts. This is caused by a gene located on the sex chromosome where slow feathering is dominant to rapid feathering and controls the rate of wing and tail feathering in the chicken. The dominant slow-feathering characteristic is passed from mothers to their sons and the rapid feathering characteristic from the fathers to their daughters. Fathers also pass the rapid-feathering gene to their sons but this is not expressed because it is recessive.
Small poultry farmers whose operations are not of sufficient size to warrant hiring a chicken sexer must wait until the hatchlings are four to six weeks old before learning the sexes of their chickens. At that time their secondary sex characteristics begin to appear, making it possible for anyone with a minimal amount of training to sex a chicken.
Instrument or machine sexing of chickens has almost disappeared, because the instruments are no longer available and spare parts cannot be obtained. The Keeler Optical (English) or Chicktester (Japanese) machine features a blunt ended telescopic tube, containing a light. The sexer inserts the tube into the evacuated cloaca and with the help of the light can identify either testis or ovaries. Successful development of this technique depends on the capability of the student and their level of experience. The steps for instrument sexing are as follows:
Hold the instrument in one hand and the chicken as for vent or cloacal sexing (first three points). Thumb and first two fingers should be on either side of the chicken at thigh level. Use thumb and first two fingers to provide slight pressure near the vent to evacuate faecal contents.
- Gently insert the glass tip of the machine into the chicken´s vent and down the large intestine. Extreme care is needed not to puncture the large intestine.
- Use one eye to look through the instrument while keeping the other eye open.
- The testicles are observed to the right of the backbone and look like a grain of rice usually a white/yellow colour, some breeds exhibit a bit of black.
- If there are no testicles on the right, move the instrument to the left of the backbone and locate the ovary. This ovary is yellowish and shaped like an inverted triangle. The right ovary is diminished and unclear.
In popular culture
- Chick sexing was featured in episode 7 of Dirty Jobs.
- Chick sexing is Steve Smith's summer occupation on the November 16, 2008 episode of American Dad! S04E06.
- Chick sexing was an important mode of employment for second-generation Japanese Americans (Nisei), who dominated the trade between the late 1930s and 1950s.
- The 'example of the chicken sexers'[clarification needed] is famous in several debates in philosophy, especially in the internalism/externalism debate in epistemology.
- In Mr. Accident (2000) comedy Sunday Valentine (Helen Dallimore) works in an egg factory doing chick sexing.
- In the Indecision episode of QI, they briefly mentioned chicken sexing.
- In a 2013 White Collar episode S04E15 "The Original", chicken sexing is mentioned by the main character Neal.
- Chicken sexing is referred to in Joshua Foer's book Moonwalking with Einstein
- Kemsley, Max (3 June 2010). "Chicken sexing". Department of Agriculture, Fisheries and Forestry (Queensland). Retrieved 13 January 2013.
- Hatchery Horrors: The Egg Industry's tiniest victims. Mercy for Animals.
- New Investigation Reveals Horrific Cruelty at 'Humane' Chicken Hatchery. Mercy for Animals. Retrieved 17 October 2013.
- Robinson Bosk, Beth. "Sexing Day-Old Chicks: How to Identify Pullets and Cockerels". motherearthnews.com. Retrieved August 30, 2015.
- Lloyd, Prof. E.A. "Sexing Baby Chicks". AG Annex. Retrieved August 30, 2015.
- Ultimate Foul Wikipedia
- Poultry: Sexing of day-old chicks as a sport
- How to tell the sex of Chicks - including general signs, breed specific tips and old wives tales.
- The art of chicken sexing - full article (PDF)