There are a large number of heritage breeds including Plymouth Rocks (of which barred is a variety). Here is the definition of heritage breeds from the Livestock Conservancy (http://www.livestockconservancy.org/index.php/heritage/internal/heritage-chicken):
Chickens must meet all of the following criteria to be marketed as Heritage.
Heritage Chicken must adhere to all the following:
- APA Standard Breed
Heritage Chicken must be from parent and grandparent stock of breeds recognized by the American Poultry Association (APA) prior to the mid-20th century; whose genetic line can be traced back multiple generations; and with traits that meet the APA Standard of Perfection guidelines for the breed. Heritage Chicken must be produced and sired by an APA Standard breed. Heritage eggs must be laid by an APA Standard breed.
- Naturally mating
Heritage Chicken must be reproduced and genetically maintained through natural mating. Chickens marketed as Heritage must be the result of naturally mating pairs of both grandparent and parent stock.
- Long, productive outdoor lifespan
Heritage Chicken must have the genetic ability to live a long, vigorous life and thrive in the rigors of pasture-based, outdoor production systems. Breeding hens should be productive for 5-7 years and roosters for 3-5 years.
- Slow growth rate
Heritage Chicken must have a moderate to slow rate of growth, reaching appropriate market weight for the breed in no less than 16 weeks. This gives the chicken time to develop strong skeletal structure and healthy organs prior to building muscle mass.
Chickens marketed as Heritage must include the variety and breed name on the label.
Terms like “heirloom,” “antique,” “old-fashioned,” and “old timey” imply Heritage and are understood to be synonymous with the definition provided here.