Is the risk-strategy efficient for the selection of breeds?

Utilisation and conservation of farm animal genetic resources 139

Chapter 6. Selection of breeds for conservation

only to proportionality Bennewitz et al., 2006. When, in addition, the loss of within breed diversity will be considered, estimates of the efective population size are required for the quantiication of the expected drit. It should be noted that the breeds selected for conservation based on their conservation potentials are not necessarily the most endangered breeds, making the results of the maximum-diversity-strategy diferent from the risk-strategy. For example, the correlation between the extinction probabilities and conservation potentials was only around 0.4 in the study of Bennewitz et al. 2006, involving 44 North Eurasian cattle breeds. In Box 6.4 an example of the results of the maximum-diversity-strategy is presented. Box 6.3. he extinction probabilities of breeds. he extinction probability of a breed is deined as the probability that a breed will go extinct at some point within a deined future time horizon e.g. 25 or 50 years. he problem in modelling, and consequently in estimating these probabilities, is that extinction of a breed is a rare event and therefore any model validation and formal model comparison is almost impossible. A semi-quantitative method was applied to a set of 49 African breeds by Reist-Marti et al. 2003. hese authors scored the breeds for four variables related to the population population size and its change over time, distribution of the breed and risk of discriminate crossing, four related to the environment organisation among farmers, existence of a conservation scheme, political situation and reliability of the information and two related to the value of the breeds presence of special traits and cultural value. he extinction probabilities of the breeds were calculated as the sum of the 10 variables and were re-scaled to a value between 0.1 and 0.9 in order to prevent extreme probabilities. Probabilities of zero and one were not allowed, because the future cannot be foreseen. his approach is appealing, because of its comprehensiveness. Simianer 2005b argued that the extinction probability of a breed is directly related to the rate of inbreeding. Following this, he obtained extinction probabilities as 12 N e and multiplied them by a constant to obtain reasonable values. herefore these probabilities can be interpreted as relative rather than absolute probabilities. he same holds true for the estimates obtained from the Reist- Marti method. he problem of these two methods is that they do not produce any standard errors or conidence intervals of the extinction probabilities. A quantitative method adapted from conservation biologists was used by Bennewitz and Meuwissen 2005. his method is based on a time series approach and involves a random process to predict likely future population size based on recent census data. On the one hand, the method produces absolute rather than relative extinction probabilities and also conidence intervals for the probabilities. However, the extinction probabilities were either close to zero or close to one and the conidence intervals covered almost the whole parameter space. he reason may be, that this method is tailored to wildlife populations, which show much greater amplitudes in population size over time. 140 Utilisation and conservation of farm animal genetic resources Jörn Bennewitz, Herwin Eding, John Ruane and Henner Simianer Although conservation potentials are very useful for prioritising, they do not tell us anything about the optimal allocation of the budget with respect to maximising the conserved diversity. For the optimal allocation of the budget, the analysis has to involve a cost function for the reduction of extinction probabilities of the breeds Weitzman, 1993; Simianer, 2002; Simianer et al., 2003. More precisely, this method assumes that marginal costs and marginal returns in diversity of conservation activities can be speciied for each breed. he total budget available for conservation is then allocated over the selected breeds using an iterative algorithm in order to maximise the conserved diversity. See Box 6.5 for further details of the optimum allocation approach. An alternative to the use of conservation potentials is the so-called ‘safe set+1’ approach as used by haon d’Arnoldi et al. 1998 and Eding et al. 2002. Following this, a safe Box 6.4. Example of the application of the maximum-diversity-strategy. Bennewitz and Meuwissen 2006 used a small data set consisting of nine Dutch cattle breeds genotyped for a number of microsatellite markers to demonstrate the maximum-diversity-strategy. hey used the Maximum-Variance-Total core set diversity measure chapter 5. he marginal diversities md considered the expected loss of between breed diversity due to extinction of breeds and the expected loss of within breed diversity due to drit. he prioritising of breeds for conservation could be done accordingly to the conservation potentials CP. Breed Efective population size 1 Extinction probability md i 2 CP i 3 Belgian Blue 370 0.027 11.14 0.301 Dutch Red Pied 68 0.147 34.17 5.023 Dutch Black Belted 154 0.065 32.22 2.094 Limousine 400 0.025 154.74 3.869 Holstein Friesian 1000 0.001 23.61 0.024 Galloway 23 0.435 190.48 82.859 Dutch Friesian 294 0.034 5.82 0.198 Improved Red Pied 111 0.090 41.77 3.759 Blonde d’Aquitaine 217 0.046 8.31 0.382 1 he efective population sizes were taken from the database of the EAAP. 2 md describes how much the expected future diversity would change with respect to a small reduction in a breed’s extinction probability. 3 CP describes how much the expected future diversity would change if a breed was made completely safe, i.e. CP = md × extinction probability.