Selective Breeding: Selecting the best to produce the next generation of animals or plants
Selective breeding is the foundation of agriculture as we know it today. Without selective breeding, crops and livestock would be much more disease prone and far less productive. The basic concept of selective breeding is quite simple. It consists of selecting those plants or animals which show the desirable characteristics as the parents for the next generation in the breeding program, and to do so repeatedly over many generations.
A good illustration of what selective breeding can achieve is the substantial difference between today's meat chicken and a chicken bred for table eggs (a so called layer bird). Read more
Selective breeding is particularly effective in situations where the reproductive cycle is short (i.e. a chicken becomes sexually mature within less than 6 months), the number of offspring are high (a chicken can produce more than 200 eggs in one year) and the breeding effort is focused and involves a large number of animals (breeding programs for meat chickens are undertaken by a small number of specialised companies involved in an international effort). It is easy to see why selective breeding has been so successful in the meat chicken industry.
All agricultural endeavours fundamentally revolve around selective breeding. Dairy cows produce more milk, wheat crops are more abundant, corn cobs are juicier, sugar cane has a greater sugar content, sheep grow finer and more wool etc ... all due at least to some extent to selective breeding. Nevertheless, it is important to acknowledge that many other factors such as nutrition, animal and plant health, animal husbandry and farming techniques also contribute substantially to successful and sustainable farming.
Change in Focus over the Past 50 Years
The focus of meat chicken breeding has evolved quite dramatically over time. While the basic science remains unchanged, the approach to selective breeding has generally become more sophisticated. In the 1960s, the goal of selective breeding in meat chickens was in essence increased growth rate and increased meat production (i.e. producing larger chickens in less time). That approach has given way to a much more balanced effort by today's breeding companies. This is illustrated in Figure 1 below, where 1960 goals are compared with those in 2013. It 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.
The main genetic selection criteria are illustrated in a different way in Figure 2 below. Note that the size of the sectors of the circle does not represent the relative importance and each sector represents a number of traits (i.e.genetically determined characteristics). Modern breeding efforts aim for a well rounded breed that exhibits a range of important characteristics, with good growth being but one of a very broad spectrum.
Figure 2: Schematic representation of the development of trait inclusion in a modern breeding program
Source: Laughlin, K.F. 2007. The Evolution of Genetics, Breeding and Production, Temperton Fellowship, Report No. 15.