Broiler

Before the development of modern commercial meat breeds, broilers were mostly young male chickens culled from farm flocks. Pedigree breeding began around 1916. Magazines for the poultry industry existed at this time. A crossbred variety of chicken was produced from a male of a naturally double-breasted Cornish strain, and a female of a tall, large-boned strain of white Plymouth Rocks. As a second example, color sexing broilers was proposed by Shaver in 1973. The genetics were based on the company's breeding plan for egg layers, which had been developed in the mid-1960s. A difficulty facing the breeders of the color-sexed broiler is that the chicken must be white-feathered by slaughter age. After 12 years, accurate color sexing without compromising economic traits was achieved. Artificial insemination provides a number of benefits relating to reproduction in the poultry industry. Broiler breeds have been selected specifically for growth, causing them to develop large pectoral muscles, which interfere with and reduce natural mating. The amount of sperm produced and deposited in the hen's reproductive tract may be limited because of this. Additionally, the males' overall sex drive may be significantly reduced due to growth selection. Artificial insemination has allowed many farmers to incorporate selected genes into their stock, increasing their genetic quality. Abdominal massage is the most common method used for semen collection. During artificial insemination, semen is most frequently deposited intra-vaginally by means of a plastic syringe. In order for semen to be deposited here, the vaginal orifice is everted through the cloaca. This is simply done by applying pressure to the abdomen of the hen. The semen-containing instrument is placed 2–4 cm into the vaginal orifice. As the semen is deposited, the pressure applied to the hen's abdomen is released simultaneously. The person performing this procedure typically uses one hand to move and direct the tail feathers, while using the other hand to insert the instrument and semen into the vagina. == General biology ==

Modern commercial broilers, for example, Cornish crosses and Cornish-Rocks, are artificially selected and bred for large-scale, efficient meat production. They are noted for having very fast growth rates, a high feed conversion ratio, and low levels of activity. Modern commercial broilers are bred to reach a slaughter-weight of about in only 5 to 7 weeks. Modern crosses are also favorable for meat production because they lack the typical "hair" which many breeds have that must be removed by singeing after plucking the carcass. Both male and female broilers are reared for their meat. Behavior Broiler behavior is modified by the environment, and alters as the broilers' age and bodyweight rapidly increase. For example, the activity of broilers reared outdoors is initially greater than broilers reared indoors, but from six weeks of age, decreases to comparable levels in all groups. The same study shows that in the outdoors group, surprisingly little use is made of the extra space and facilities such as perches – it was proposed that the main reason for this was leg weakness as 80 per cent of the birds had a detectable gait abnormality at seven weeks of age. There is no evidence of reduced motivation to extend the behavioral repertoire, as, for example, ground pecking remained at significantly higher levels in the outdoor groups because this behavior could also be performed from a lying posture rather than standing. Examining the frequency of all sexual behaviour shows a large decrease with age, suggestive of a decline in libido. The decline in libido is not enough to account for reduced fertility in heavy cocks at 58 weeks and is probably a consequence of the large bulk or the conformation of the males at this age interfering in some way with the transfer of semen during copulations which otherwise look normal. Feeding and feed conversion Chickens are omnivores and modern broilers are given access to a special diet of high protein feed, usually delivered via an automated feeding system. This is combined with artificial lighting conditions to stimulate eating and growth and thus the desired body weight. In the U.S., the average feed conversion ratio (FCR) of a broiler was 1.91 kilograms of feed per kilograms of liveweight in 2011, an improvement from 4.70 in 1925. Canada has a typical FCR of 1.72. New Zealand commercial broiler farms have recorded the world's best broiler chicken FCR at 1.38. The microbiome of the broiler also has a large effect in addition to the birds nutrition and genetics on overall FCR. == Welfare issues ==

Artificial selection has led to a great increase in the pace of which broilers develop and reach slaughter-weight. Increased inactivity is linked with an increase in dermatitis caused by a greater amount of time in contact with ammonia in poultry litter. Many broilers die during the processes of catching, packing and transport. == World production and consumption ==

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. 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. Worldwide, 86.6 million tonnes of broiler meat were produced in 2014, and , the worldwide estimation of broiler chick population was approximately 23 billion. == Impacts of climate change ==