Standard intensively farmed broilers are usually:

Reared under high stocking densities without outdoor access: EU legislation permits a maximum stocking density of 33 kg/m² (16.5 birds/m² for a 2kg bird). However two derogations permit density increases to 39 and 42 kg/m² (19.5 and 21 birds/m² for 2kg birds, respectively). High densities do not provide chickens with the space they require to live comfortably and contribute to poor walking ability in the birds.
Bred for very fast growth, high meat yield and feed efficiency: reaching market weight (~2.2kg) in less than 36 days (around 5 weeks of age), compared to 56 days for intermediate growth rate breeds and 80-120 days for slow growing and traditional breeds. Fast growth rate, associated conformation changes, and breed are major contributors to cardiovascular and metabolic diseases in chickens as well as lethargy and poor walking ability.
Inactive: in their last weeks of life, broilers spend more than 85% of their time inactive. This is largely due to cardiovascular strain in pushing blood to such a high breast muscle mass and walking difficulties related to changes in conformation and walking style or difficulties, compounded by a lack of a stimulating environment. By comparison, slower-growing breeds spend significantly more time ranging and exploring their environment and 50% more time perching when compared to fast growing breeds. During feeding, slower-growing breeds also exhibit more exploratory pecking and spend more time performing preening and scratching behaviours.
Reared in barren environments: broiler sheds are generally bare except for feeding and drinking points and litter (such as wood shavings) on the floor. Provision of natural light is mixed within and between countries and light levels tend to be quite low (set at a minimum of 20 lux in the EU).

Maximum stocking density in the UK is limited to 39kg/m² under the Schedule 5a of Welfare of Farmed Animals (England) (Amendment) Regulations 2010 and 38kg/m2 under Red Tractor Farm Assurance Poultry Scheme). Some producers provide natural light via windows and environmental enrichment through the provision of straw bales and perches.

Standard intensive broiler production