136 Utilisation and conservation of farm animal genetic resources
Jörn Bennewitz, Herwin Eding, John Ruane and Henner Simianer
Ruane 2000 suggested a framework for prioritising breeds for conservation on the national level and applied this to 45 Norwegian breeds covering 17 species. He scored
breeds for the following criteria: degree of endangerment mainly determined by the current population size plus some additional factors, traits of current economic value,
special landscape value, traits of current scientiic value, cultural and historical value and genetic uniqueness. He suggested to use the scoring list for the selection of breeds
for conservation. He did not propose a general algorithm for combining scores for the diferent criteria, arguing that this would depend on country-speciic conditions and
priorities. He suggested nevertheless that the degree of endangerment should be the most important criterion.
5. Is the maximum-diversity-strategy efficient for the selection of breeds?
Using the maximum-diversity-strategy, a breed is selected for conservation that contributes signiicantly to the genetic diversity. he prerequisite for this approach is that
an appropriate diversity measure is used that relects the objective of the conservation program. In chapter ive diferent diversity measures were described, that difer from
their conceptual point of view as well as in the weighing of the between- and within- breed diversity. In the following it will be shown how diversity measures can be used for
selection of breeds for conservation. For the relative importance of the between- and within-breed diversity, and hence the choice of the appropriate diversity measure for
the selection of breed, see Box 6.2.
Following the maximum-diversity-strategy, breeds can be ranked according to their contribution either to the actual or to the expected future diversity. he drawback of
ranking breeds according to their contribution to the actual diversity is that the loss
Table 6.2. Risk categories based on inbreeding rate ∆F used by the EAAP 1998.
Risk category ∆F over 50 years
Critically endangered 40
Endangered 26 – 40
Modestly endangered 16 – 25
Possibly endangered 5 – 15
Not endangered 5
Note: he following additional elements are used to adjust the risk category by one category: proportion of registration in the herd book, change in the number of breeding animals, percentage of pure breeding and
immigration and number of herds.
Utilisation and conservation of farm animal genetic resources 137
Chapter 6. Selection of breeds for conservation
of between breed and within breed diversity over time due to extinction of breeds and genetic drit is not accounted for. Hence, it seems to be better to rank the breeds according
to their contribution to the expected future diversity, as it will be shown next.
Assume that there are a number of N breeds included in the analysis and for each breed
the probability is known that it will go extinct within a deined future time horizon t
e.g. 50 years, the extinction probability z. At the end of the deined time horizon there
are 2
N
diferent possibilities of present and extinct breed combinations possible, i.e. there
Box 6.2: Relative importance of between and within breed genetic diversity. In chapter 3 it was shown how diversity can be partitioned into between-breed diversity
D
B
and within-breed diversity
D
w
. he question is, which component is more relevant for conservation and hence for the selection of breeds for a conservation plan. Fabuel
et al. 2004 investigated the impact of a diferent weighing factor λ in the combination of the two components, i.e. λ
D
w
+ D
B
, and obtained diferent breed conservation priorities, depending on λ. Following this, the determination of the relative importance of these two components is crucial and it determines the
choice of the diversity measure chapter 5 that has to be used in the maximum-diversity strategy for the selection of breeds. For instance, if only the between-breed diversity shall be considered
λ = 0, the Weitzman diversity measure might be appropriate. However, if both between- and within-breed diversity shall be taken into account, the core set diversities maybe used. he
Maximum-Variance-Total core set diversity measure maximises the variance of a hypothetical quantitative trait and gives more weight to the between-breed diversity λ = 0.5, as pointed out
by Toro
et al. 2006 than the Maximum-Variance-Ofspring λ = 1 does. A stronger weighing of the between-breed diversity might be appropriate when conserved breeds
are considered to be used in a crossbreeding plan, because both heterosis and complementarity are a function of this type of diversity Fabuel
et al. 2004. Additionally, as argued by Piyasatian and Kinghorn 2003 and Bennewitz
et al. 2006, the between-breed diversity is more accessible, because of the speciic gene and allele combination that can be found in diferent breeds. his
allows a faster adaptation of commercial breeds to changes in the production environment or in market needs by introducing genetics from a conserved breed. However, a too strong weighing of
between-breed diversity results in ignoring most of the total diversity. he within-breed diversity might be important for the creation of a new synthetic breed that copes with a challenging
environment. On the other hand, an over-emphasis on within-breed diversity will favour large breeds, which are not endangered. Additionally, the better accessibility of the between-breed
diversity is not accounted for. In summary, it seems that a diversity measure should be used that considers both components of
diversity with a weight that is not arbitrarily chosen by the researcher but is given by the deinition of the appropriate diversity measure and chosen according to a well deined conservation
objective.
