Effects of Selective Breeding: A School-based Experiment
An experiment conducted by students from James Ruse Agricultural High School in Carlingford, NSW has busted a commonly-held belief about Australian chickens and in the process demonstrated the dramatic effects achieved through decades of selective breeding efforts. If a school group is interested in undertaking a similar experiment themselves, please click here.
Selective breeding is a process of developing a breed of bird to have particular characteristics by choosing to mate only the best cockerels – that is, those that demonstrate the desired characteristics, such as those which grow better, are healthier or have more meat - with the best hens. To read more about modern Selective Breeding, click here.
The great grandparents of the chickens we eat in Australia today were bred overseas using conventional genetic selection techniques and were imported into Australia as fertile eggs. The next generations (the grandparents, parents and ultimately the meat chickens reared for eating) are then bred and grown on farms here in Australia.
Selective breeding is different from genetic modification. There are no genetically modified chickens in Australia.
The School Experiment
In early 2007, the Year 10 school students compared the growth of chickens bred to lay eggs with chickens bred for meat when fed the same feed and held under identical conditions and found that over six weeks the meat chickens grew four times bigger than the egg chickens. The experiment used one day old chicks obtained from a commercial hatchery.
The research debunks the commonly held misconception that the larger size and better growth rates of the chickens we eat today is due to the use of hormones. Last year, research released by the Australian Chicken Meat Federation (ACMF) revealed that almost 80% of Australians believe that something, for example growth hormones, is added to Australian chickens to make them grow artificially larger, despite the fact that hormones have not been used in the production of meat chickens in Australia for over 40 years.
The school sourced 15 egg-laying chickens and 15 meat chickens as day old chicks from a commercial supplier, and the students hand raised them. All chickens were fed the same standard chicken feed product, made mostly from cereal grains and protein sources, obtained from a local feed supplier. The chickens were checked every day and weighed regularly for a period of six weeks. At the end of the six week period, the average weight of the chickens bred for egg laying was 592g while the chickens bred for meat was more than four times larger, weighing in at 2,388g.
Lisle Brown, Head Teacher of Agriculture at James Ruse Agricultural High School, said the students enjoyed busting a common myth, one which some had probably held themselves. “This project enabled the students to observe first hand the great effect selective breeding has on the growth and development of chickens and enabled our students to see how the meat chicken industry in Australia is able to produce the large volume of chicken meat we eat today,” he said.
“Students were also able to put into practice all the elements that make a good reliable scientific experiment, such as randomisation, replication, standardisation and control.”
Here are a few pictures that demonstrate the effect of many decades of dedicated selective breeding work. They show the egg chicken (the red/brown bird in the photo, also referred to as layer) and the meat chicken (the white bird in the photo, sometimes also called as broiler). In this experiment, the actual commercial strains of chickens used were Isa Brown layers and Cobb 500 broilers. These pictures were taken on day 38.
Picture 1: Layer Chicken (about 463g) at 38 days of age
Picture 2: Broiler Chicken (about 2.25kg) at 38 days of age
Picture 3: Group Photo with Layer and Broiler of same age(38 days)
The Graph below shows the averaged results for one of the two school trials, illustrating the substantial difference in growth rate between egg chickens and meat chickens.
Interested in trying this out yourself? If your school has appropriate facilities to look after chickens, has had previous experience in keeping chickens, and has someone with suitable experience with raising chickens to supervise this project, please click here.
Answers to Some Frequently Asked Questions or download as as a separate PDF by clicking here.
This story was the subject of an ACMF Media Release issued on 23 July 2007.