Selection and Mating

Selection and mating systems are the foundation for genetic improvement. Basically, selection allows breeders to positively alter genotypes, with an additive mode of inheritance, that influence a trait and mating systems lets breeders take advantage of heterosis and breed complementarity. Before deciding on a selection and mating scheme it is first important to set goals for your operation, often called Breeding Objectives. Determining breeding objectives should start with assessing your management, resources and market opportunities (Chapter3 Assessing Management Resources and Marketing). Well developed breeding objectives should be the focal point of determining your mating scheme, traits that should be selected for, and magnitude and direction of selection pressure to be placed on those traits.

When considering selection and mating decisions it is essential to understand the genetic mechanisms of the traits under consideration. For example, many important traits are monogenic traits - traits influenced by only a single gene locus. Monogenic traits include traits such as coat color and many genetic defects. Other traits are influenced by many genes, such as those for which EPDs are computed, and they are called polygenic traits.

Mating schemes are dependent on the type of operation (seedstock or commercial) and the level of heterosis that is desired. Breed selection is another factor in setting up a mating scheme. Options include pure/straight breeding, crossbreeding and composite breeding, each having advantages and disadvantages depending on the factors previously mentioned.