Are Chickens Pumped With Hormones? (Why They're 4x Bigger)

Two chickens, same age, same food. One weighs under a kilo, the other over four. Most people say "hormones". It isn't true, and the real answer is stranger. Hormones have been banned in US chicken since the 1959 ban on the DES pellet, and antibiotic growth boosters are banned in Europe too. So what turned the chicken into a giant? We look at what the critics get right first (leg problems, struggling hearts, woody breast, and the Better Chicken Commitment's push for slower-growing breeds), then go back to the 1948 "Chicken of Tomorrow" contest and the diet-swap experiment that showed it's mostly genes: about 70 years of choosing parents. ⏱ Chapters 0:00 Same age, same food: 1 kg vs 4 kg 0:29 Is it hormones? 1:06 What the critics get right 1:55 The Chicken of Tomorrow 2:29 The experiment that proved it 3:17 How old is the chicken on your plate? 3:49 How big is too big? 📚 Sources • Zuidhof MJ et al. (2014). Growth, efficiency, and yield of commercial broilers from 1957, 1978, and 2005. Poultry Science 93(12):2970–2982. doi:10.3382/ps.2014-04291 • Havenstein GB, Ferket PR, Qureshi MA (2003). Growth, livability, and feed conversion of 1957 versus 2001 broilers when fed representative 1957 and 2001 broiler diets. Poultry Science 82(10):1500–1508. • Knowles TG et al. (2008). Leg disorders in broiler chickens: prevalence, risk factors and prevention. PLoS ONE 3(2):e1545. • Julian RJ (1998). Rapid growth problems: ascites and skeletal deformities in broilers. Poultry Science 77(12):1773–1780. • Che S et al. (2022). Prevalence of breast muscle myopathies in broiler chickens from Ontario, Canada. PLoS ONE. • Torrey S et al. (2021). In pursuit of a better broiler: growth, efficiency, and mortality of 16 strains of broiler chickens. Poultry Science. • USDA FSIS: Meat and Poultry Labeling Terms; FDA: Steroid Hormone Implants Used for Growth in Food-Producing Animals • TIME (Dec 21, 1959): Hormones & Chickens; European Commission (2005): ban on antibiotics as growth promoters; FDA Guidance for Industry #213 • National Chicken Council: U.S. Broiler Performance (USDA data); NCC/ORC International consumer survey (2015) • RSPCA: Chickens reared for meat; Our World in Data (Ritchie, 2023): slower-growing breeds • Better Chicken Commitment; Poultry World (BCC progress); World Animal Protection UK (Mar 2026) • National Geographic (McKenna, 2017): How the "Chicken of Tomorrow" contest created the bird we eat today Chicken sizes and growth curves are simplified from the studies; the breeding loop is a simplified picture of modern multi-trait breeding. Narration: AI voice. Animation: Why Guy. 🔔 Subscribe for a new "why" every day. #chicken #hormones #whyguy,