Mate Selection For Sustained Genetic Improvement In Small Populations

Abstract

In genetic improvement there is an infinite range of actions, but in reality only two critical control points - animal selection and mate allocation. Because the best animals to select depend on the pattern of mate allocation, and vice versa, these decisions can be made simultaneously as Mate Selection. When we specify the implementation of the breeding program using a Mate Selection approach, we automatically incorporate decisions on factors such as breeding objectives, selection intensity, crossbreeding, inbreeding avoidance, which animals to take semen and embryos from, migration of sires between herds, and how much to spend on seed stock purchase, transport, etc. Moreover, we can also satisfy any logistical constraints we impose, such as quarantine restrictions on animal movements. The primary costs associated with genetic improvement are for progeny testing programs and associated facilities. A successful program depends on both the size of the testing facility and the way it is managed. The total number of animals housed is divided into a number of genetic nucleus lines or populations. The use of more lines means more breeding objectives that can be targeted but it also implies a reduction in the size of lines, particularly those considered "minor" or "experimental". Maintaining many small populations also has applicability in the area of animal genetic resource management (e.g., critical and endangered breeds; Gandini et al., 2004). However, larger lines allow for increased opportunities for improving traits that are expensive to measure and breeding for difficult traits (e.g., sex-linked, low heritability) but imply that fewer lines can be kept within the same testing capacity. Thus, the whole process of allocating resources becomes a population size optimization problem. The rate of inbreeding quantifies the risk of increased relationships and is an objective criterion used to manage population size. Closer relationships are generated when high genetic gains are targeted, when the breeding populations are small or even when they are large but the traits to be improved force the intense use of family information. The objective of this study was to assess the effectiveness of Mate Selection to manage genetic improvement and diversity in a set of relatively small simulated pig populations.