Cobb 500

The Cobb 500 is a fast-growing broiler chicken breed. They can reach a 2 kg slaughter weight at 33 days old.^[1][2] They make up around half of all globally farmed chickens as of 2016.^[3] The Cobb 500 is controversial due to their health problems. Animal rights and animal welfare groups such as Open Cages have called for the industry to stop their use.^[4][5]

The Cobb linage descends from the Vantress chicken, which was bred for the USDA's Chicken of Tomorrow contest in the 1940s.^[6] The Cobb line itself saw its initial development in the 1970s in England by Cobb-Vantress.^[7] The Cobb 500 in particular was introduced into the United States in 1985. In response, the US producer Tyson Foods acquired a 50% stake in Cobb-Vantress in 1986.^[8] In 1994, Tyson acquired full control of the company.^[9] The Cobb 500's share of all chickens has increased in the decades since.

In 2008, all Cobb line birds made up around 30-40% of global broilers.^[10] In 2016, the Cobb 500 alone was nearly 50%.^[3] More broadly, fast-growing chickens now make up the vast majority of the global chicken supply. As of 2021, 90% of the global broiler population is part of either the Cobb or Ross lines, which are both fast-growing.^[11]

The fast growth of the Cobb 500 is associated with an increased rate of various health problems. Compared to slower-growing chickens, they have a higher rate of sudden death syndrome,^[12] hock burns,^[13] Tibial dyschondroplasia,^[14] weaker disease resistance and antibody response,^[15] bone deformations, and problems with walking.^[16]