Selective breeding – why is it important and what does it mean?

Selective breeding – why is it important and what does it mean?

In an earlier blog, I described how modern meat chickens have been selectively bred to grow well and put on a lot of muscle (meat), in the context of explaining that these characteristics have been achieved without the use of hormones (hormones not having ever been fed or in any way administered to meat chickens in Australia for over 50 years) – see: Chookchat – the hormone myth

In another blog, I explained how different selective breeding paths had led to separate chicken breeds for commercial meat chickens and egg laying chickens which not only perform very differently (one grows to a large body size and carries lots of meat; the other produces lots of eggs), but which also look quite different too.

In this month’s blog, I’ll explain a little bit more about how traditional selective breeding works in the modern chicken meat industry, why we do it, and what the impacts are for the chickens, the industry and consumers.

Selective breeding – why?

First, a bit of background.

Since the time man first domesticated animals, selective breeding has been used to develop better or more useful strains (or breeds) of the animals from the genetic diversity that naturally exists in the population of a single species.

Heard of Charles Darwin? Well, he was the first to describe the connection between domestication, selection and evolution. In the first chapter of his famous book, “On the Origin of the Species”, Darwin discussed how domestication and selective breeding had produced significant changes over time in a range of animals, including dogs, cattle and pigeons. He went on to expand on how deliberate selective breeding by man has been used to create desired changes in domesticated animals in his 1868 book “The Variation of Animals and Plants under Domestication”.

Just consider what we’ve done with the following animals:

Dogs – Through selection and cross breeding, a vast diversity of breeds of dog has been developed over the centuries, including breeds which are highly suited for:

  • Herding livestock – e.g. Border Collies, Cattle Dogs and Corgis (yes, Corgis were bred for herding cattle and sheep!)
  • Hauling and pulling – e.g. Siberian Huskies
  • Hunting – e.g. Retrievers to retrieve kills during a hunt, Spaniels for flushing birds out of bushes, Rhodesian Ridgebacks for hunting lions, and Terriers for finding, digging out and killing rats and other vermin
  • Guarding and protection – e.g. Doberman Pinscher
  • Lapdogs – for, well, keeping your lap warm I guess!

Dog breeds

Photography: www.istockphoto.com

Horses – some were developed for heavy work like ploughing or pulling carts (e.g. Clydesdales), some for carrying men to war, some for speed and racing (e.g. Thoroughbreds).

Cattle – like all domesticated animals, cattle have been bred to be quieter and more manageable. Different breeds of cattle have also been developed which either produce more milk (e.g. Friesians and Jerseys) or more meat (e.g. Charolais).

Chickens – different breeds have been developed that are smaller (bantams), or produce more eggs, or which are larger and more ‘meaty’, or just aesthetically unique!

Some fancy breeds of chicken were just bred for their good looks!

Some fancy breeds of chicken were just bred for their good looks!

A modern hybrid meat chicken

A modern hybrid meat chicken

All of this has been achieved using a very simple ‘tool’ – and that is selective breeding.


How is it done?

The principle of selective breeding is simple – it relies on the selection of individual animals which show the most desirable characteristics as the parents for the next generation in the breeding program, and repeating this process over many generations.

Selective breeding is particularly effective for animals that have a short reproductive cycle, the number of offspring are high and the breeding effort is focused and involves a large number of animals. This fits the chicken perfectly because a chicken becomes sexually mature within less than 6 months and can produce more than 200 eggs in one year. There are currently a small number of specialised breeding companies that undertake programs for meat chickens as part of an international effort to produce the ideal meat chicken! These efforts have been going on for decades, so it is easy to see why selective breeding has been so successful in the meat chicken industry.

Does selective breeding make something a Genetically Modified Organism?

No!

Genetic engineering, often referred to as genetic modification, is the direct manipulation of an organism’s genome (set of genes) using biotechnology. It could, for example, involve extracting the genes from one plant or animal and inserting them into the genome of a totally different species. Genetically Modified Organisms (GMOs) are generally defined as organisms in which the genetic material has been altered in a way that does not occur naturally by mating and/or recombination.

Traditional selective breeding, on the other hand, leads to gradual but cumulative changes in a population of animals over time using natural processes. Selective breeding therefore does not make an animal a Genetically Modified Organism, and modern breeds of chickens are no more Genetically Modified than your pet Poodle or Labrador.

So, the breeding of modern meat chickens isn’t something out of science fiction; but is it rocket science? Well, the answer is yes and no! No, because the principle is so simple – just mate the animals with the most desirable characteristics with each other to produce the next generation. And yes? Because the technologies used to choose the best parents to produce the next generation from can be cutting edge. For example, chicken breeding companies have used an X-ray unit called a lixiscope to identify subclinical leg bone abnormalities in meat chicken breeding stock, allowing them to actively select against its presence in breeding stock, thereby improving overall leg health in meat chicken breeds – funnily enough, the lixiscope was in fact developed by NASA scientists! Meat chicken breeding companies have also used a technique called pulse oximetry to measure the oxygen saturation levels in the blood of chickens, an important indicator of susceptibility to several metabolic diseases, in order to develop breeds which have stronger cardio-vascular and respiratory systems.

Will we ever see GM chickens used commercially?

I preface my comments here by saying that I’m personally not opposed to the use of Genetic Modification (GM) technologies to improve agricultural productivity, if it can produce significant benefits in a shorter time frame, and so long as the products are properly evaluated so that they pose no risk to the environment, human health or food safety and animal welfare.

But will the Australian chicken industry ever use breeds of chicken derived from GM technologies? Well, maybe, but I believe it would only do so if the outcome wasn’t just about improvements in productivity (i.e. something in it for the producers); it would have to be for some characteristic which has broader community or social benefit, for example, birds resistant to avian influenza.

What are meat chickens selected for?

The focus of meat chicken breeding programs has itself evolved quite dramatically over the years. In the 1960s, the goal of selective breeding in meat chickens was basically all about increased growth rate and increased meat production (i.e. producing larger chickens in less time). These days, the approach is much more balanced, with health and welfare very important breeding targets. This is illustrated in the figure below, which I have extracted from the ACMF website and which compares the 1960 breeding goals of a major meat chicken breeding company with its goals in 2013. This shows that the focus has changed from growth and yield to a broad spectrum of outcomes, with a clear emphasis on improving animal welfare, reproduction and fitness outcomes.selective breeding targets

Why is it important to the chicken industry?

It is estimated that somewhere between 60 – 80% of the significant gains in meat chicken performance that have been made over the past 60 years are due to genetic improvements made in the breeds that are available and used commercially.

These have all been made possible by traditional selective breeding.

Why should it be important to consumers of chicken meat?

Consumers have benefitted from the improvements in productivity that have resulted from the gains made through selective breeding, particularly in terms of lower prices for chicken meat, greater availability of chicken meat, and more consistent quality. It’s selective breeding that’s allowed chicken to become a regular part of our Australian diet, rather than a special treat, only affordable on special occasions (which was the case when I was a child).

And what about the chickens themselves?

You’ll have to wait and see, because in next month’s blog I’m going to discuss something that’s very close to my heart…and that’s chicken behaviour, and whether and how it might have been changed in the course of the development of modern meat chicken breeds.

So join me next month for a journey through the behavioural repertoire of a modern meat chicken.

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