Guidelines for best practice

168 Utilisation and conservation of farm animal genetic resources Theo Meuwissen 1. What issues are important? he operational issues of conservation schemes depend on which kind of conservation plan was chosen in chapter 2 and 6. he main distinction is between pure live conservation schemes, pure cryoconservation schemes, and a combination between live and cryoconservation schemes. Within the live conservation schemes, one can distinguish in situ and ex situ live conservation, but this distinction is not very relevant for this chapter because the issues that are important for in situ schemes are also important to ex situ live schemes. he issues that are important for live schemes are: the efective population size at which the breed is maintained; the selection of animals within the breed; the mating of the selected animals; the genetic improvement that needs to be achieved; the monitoring of traits and pedigree. hese issues will be addressed in paragraph 2. With respect to the issue of the selection of animals, note that some selection is possible, when sires produce more than one son and dams more than one daughter and the population is not increasing in size, but the selection may well be at random instead of for a trait. he most relevant operational issue for cryoconservation schemes is the replenishment, i.e., replacement, of retrievals from the genome bank, since retrievals will deplete the genetic materials in the genome bank. he operation of the genome bank is described in paragraph 3. he aim of the bank is to conserve genotypes rather than alleles, because, generally, we want to conserve combinations of alleles, i.e. the genotype, that leads to a characteristic of a breed instead of a particular allele. With respect to the combination of live conservation schemes and cryo-conservation schemes there are two aims: 1. A live conservation scheme is conducted while cryo-conservation serves as a back up in case the live population runs into genetic problems inbreeding; genetic diseases; loss of genetic characteristics; physical loss of a large part of the population. If old ‘back-up’ genetic material is retained, the genome bank will keep track of the full history of the evolution of the population. 2. Cryo-conservation can be actively used to increase the efective population size of a small live breed, and reduce genetic drit. • • • • • Utilisation and conservation of farm animal genetic resources 169

Chapter 8. Operation of conservation schemes

he former aim is an extension to a pure live conservation scheme, and can reduce risks substantially in these schemes. he latter aim implies a judicious use of cryoconservation, which will be given special attention in this chapter. he combination of live and cryoconservation can result in very potent conservation strategies because: It can achieve all the objectives for conservation, namely opportunities to meet future market demands, insurance against future changes in production circumstances, insurance against the loss of resources with a high strategic value, opportunities for research, present socio-economic value, cultural and historic reasons and ecological value chapter 1. It can reduce the genetic drit substantially, and resembles in that respect a pure cryo-conservation scheme where genetic drit is very small. In the combination of an in situ live and cryo-conservation scheme the population will still evolve and adapt to the environmental circumstances. In the combination of an in situ live and cryoconservation scheme we have to ind a balance between the latter two aspects: reducing genetic drit by using old, perhaps very old, cryoconserved stocks and promoting genetic adaptations by using little cryoconserved stocks. How to ind this balance will be described in paragraph 4.

2. Live conservation schemes

he efectiveness of live conservation schemes depends on the efective population size and the management of the genetic variance through an efective selection and mating of the animals.

2.1. The effective population size

From conservation biology theory, efective population sizes should exceed 500 animals; otherwise the accumulation of slightly deleterious mutations will deem the population to extinction Lynch et al., 1995. However, there has arisen a controversy over the mutation rate that was assumed. Lynch et al. assumed a mutation rate of 0.5 mutations per genome per generation mutation model A, while new estimation methods resulted in much smaller estimates of 0.03 mutations per genome per generation Garcia-Dorado et al., 1998; Caballero and Garcia-Dorado, 2003 mutation model B. Also the mean selective advantages of mutations difered between the mutation models A and B and are estimated at 0.02 and 0.2, respectively, in Drosophila Caballero and Garcia-Dorado, 2003. Hence, under the model B, mutations are rarer but have larger • • •