Genetic selection in livestock — for faster growth, higher milk production, more prolific reproduction, and disease resistance — has profound welfare implications. Some selection has created animals whose biology works against their welfare; emerging genomic tools offer the possibility of selecting for welfare-positive traits alongside production traits.
Commercial broilers have been selected for breast muscle weight, feed conversion, and growth rate since the 1950s. This selection has produced measurable welfare costs: breast myopathies (wooden breast, white striping, spaghetti meat) now affect the majority of commercial birds; cardiovascular system cannot support muscle growth demands, causing sudden death syndrome; skeletal development lags muscle growth, causing leg disorders. These are direct genetic causes of welfare compromise — the animals' biology has been optimized for production at the expense of health.
Genomic selection — using DNA markers across the entire genome — makes it possible to select simultaneously for production traits and welfare-relevant traits (lameness susceptibility, mastitis resistance, temperament, bone health). Research programs in the EU and UK are developing welfare genomics: incorporating gait scoring, bone mineral density, and immune function metrics into breeding indices alongside production traits.
Holstein dairy cows have been selected for extreme milk production (12,000-15,000 liters/lactation). This creates: negative energy balance in early lactation (body condition loss; liver stress); ketosis (metabolic disorder affecting 30-40% of high-producing cows); displaced abomasum; mastitis susceptibility; and reproductive failure. These conditions cause chronic pain and welfare compromise — at the genetic level, the cow has been optimized for milk at the expense of health.