Sexing Barred rock chickens (also called Plymouth rock chickens) before they are grown is not an exact science. As with other breeds of chicken, young Barred rock chickens less than a week old are sexed by professional chicken sexers; and even then, the sexers are correct only 90 to 95 per cent of the time. As the chickens get older, the characteristics that differentiate the pullets (young hens) and cockerels (young roosters) become more pronounced; and by adulthood, even laymen can tell the difference between the sexes of Barred rock chickens.
Observe the chicks at about a week old. Pullets generally develop wing and tail feathers before cockerels.
Observe the chicks at about five to six weeks of age. Cockerels generally develop combs at this age. The combs begin developing and turn a more prominent red colour. Cockerels at this age start to gain size over the pullets.
Observe the young chickens at two to three months of age. Cockerels will start developing hackle feathers. Hackle feathers form the rooster's "mane"--that heavy overcoat of feathers that cover the rooster's neck.
Observe the chickens from three months to nine months of age. Barred rock cockerels will have wider white "bars" in their feather pattern than Barred rock pullets. Cockerels will have a larger comb and wattle and will develop spurs on their legs.
Sexing chickens is not a foolproof task until the chicks reach adulthood. These signs and tendencies that young chickens exhibit while growing may suggest their sex, but the proof won't come until they reach adulthood. Professional chicken sexers attempt to determine the sex of a chick by examining the chick's vent. It is not recommended that laymen attempt to sex chickens using this method.