What issues are important?

174 Utilisation and conservation of farm animal genetic resources Theo Meuwissen 2.2.1. Mate selection A strategy that optimises the selection and mating in one step is called mate selection Kinghorn et al., 2002; Fernandez et al., 2001. Mate selection usually tries to maximise a selection criterion that contains genetic gain, average relationship of the selected parents, and average inbreeding of the ofspring, where the weighings of these three components need to be deined by the user. Since it is diicult to obtain such weights, and because in conservation schemes we would like to have control over the rate of inbreeding, instead of it being the result of a complicated weighing and optimisation process, we will focus on OC selection here, which directly controls the rate of inbreeding. 2.2.2. Optimum Contribution selection and Factorial-Minimal-Coancestry mating Generally we advise the following selection and mating strategy: Step 1: Use Optimal Contribution selection to determine how many ofspring each animal should get. he selection criterion is either to minimise the average kinship among the selected parents or to maximise genetic improvement whilst limiting the average kinship among the selected parents paragraph 2.3. Step 2: Use Factorial-Minimum-Coancestry mating to decide on who is mated to whom, where factorial implies that each mating pair obtains only 1 ofspring or at least as few as possible ofspring see Box 8.1. Step 1 determines the rate of inbreeding; Step 2 tries to set up matings which facilitate the OC selection in the next generation. Step 2 also avoids the mating of close relatives, which is important to avoid the occurrence of the occasional highly inbred ofspring. Since, Step 1 determined the future efective size of the population, it is much more important than Step 2 in the management of genetic variation. 2.2.3. Random - Non-sib matings he most straightforward method to mate the individuals is assigning the matings at random, e.g., when a sire should get 10 ofspring from 10 dams, the dams are sampled at random to the sire. However, some of the matings will be between close relatives, i.e., full-sib and half-sib matings. his should be avoided since the ofspring from these matings will be highly inbred and will thus show increased inbreeding depression. • • Utilisation and conservation of farm animal genetic resources 175

Chapter 8. Operation of conservation schemes