become sexually reproductive at 5 to 6 months of age. However, the bird's parents, often called "broiler-breeders", must live to maturity and beyond so they can be used for breeding. As a consequence, they have additional welfare concerns. Meat broilers have been artificially selected for an extremely high feeding motivation, but are not usually feed-restricted, as this would delay the time taken for them to reach slaughter-weight. Broiler-breeders have the same highly increased feeding motivation, but must be feed-restricted to prevent them becoming overweight with all its concomitant life-threatening problems. An experiment on broilers' food intake found that 20% of birds allowed to eat as much as they wanted either died or had to be killed because of severe illness between 11 and 20 weeks of age – either they became so lame they could not stand, or they developed cardiovascular problems. Broiler breeders fed on commercial rations eat only a quarter to a half as much as they would with free access to food. They are highly motivated to eat at all times, presumably leading to chronic frustration of feeding. Because broiler breeders live to adulthood, they might show feather pecking or other injurious pecking behaviour. To avoid this, they might be beak trimmed which can lead to acute or chronic pain. World production and consumption A report in 2005 stated that around 5.9 billion broiler chickens for eating were produced yearly in the European Union. Mass production of chicken meat is a global industry and at that time, only two or three breeding companies supplied around 90% of the world's breeder-broilers. The total number of meat chickens produced in the world was nearly 47 billion in 2004; of these, approximately 19% were produced in the US, 15% in China, 13% in the EU25 and 11% in Brazil. Consumption of broilers is surpassing that of beef in industrialized countries, with demand rising in Asia. Worldwide, 86.6 million tonnes of broiler meat were produced in 2014, and , the worldwide estimation of broiler chick population was approximately 23 billion. Broiler industry The commercial production of broiler chickens for meat consumption is a highly industrialized process. There are two major sectors: (1) rearing birds intended for consumption and (2) rearing parent stock for breeding the meat birds. See also Animal cruelty Animal welfare science Chicken Chicken tax Concentrated animal feeding operation Early feeding Intensive animal farming Poultry farming The Chicken of