Hybrid chickens are bred by crossing two or more types of purebred chickens. Hybrids are not themselves "breeds" because their offspring rarely breed true -- that is, their offspring rarely look or produce like the parents. Many commercially raised breeds of chickens are hybrids, and chicken breeders often cross purebred chickens to make ornamental, meat and laying chickens. Many types of hybrid chicken strains are protected by their producers from mimicry by other breeders.
Hybrid chicken varieties are often cheaper than pure breeds, with some exceptions, because they are often kept in larger flocks than purebred birds. Because of this, they are also economical because they are usually vaccinated young and are quite tame. Hybrids are often recommended as good beginner birds for those inexperienced with chickens.
Commonly Crossed Pure Breeds
In most cases, hybrid chickens involve crosses between Rhode Island Reds, Marans, Plymouth Rocks, Sussex or Leghorn chickens. These purebred lines are often used because of the wide availability of well-documented lines and their ideal production rates. In some cases, different crosses of the same breeds may have different registered names and qualities because of the percentage of each purebred line present in the hybrid. This is achieved by "breeding back," or breeding a first-generation hybrid back to one of the original purebred lines.
Hundreds of hybrid chicken varieties exist. Some, like Black Rocks, Isa Browns, White Stars and Bovans Goldline chickens, have registered names, while others are simply called by their crosses -- such as an Indian Game/Rhode Island Red cross. Most hybrid strains have been bred to emphasize a particular quality: appearance, meat or egg production.
Protected Hybrid Strains
Some hybrid strains have been commercially protected and given registered names -- such as "Black Rock" hybrids, which are Rhode Island Red/Barred Plymouth Rock crosses. These registered names are often limited to specific strains produced only by certain hatcheries.