Population structure and genetic diversity of Swiss sheep breeds

The year 2010 was declared by the United Nations as the International year of biodiversity. During that year, the Swiss Sheep Breeding Association made herd book data of its four largest breeds available for genetic diversity analyses. Those were Brown Headed Meat Sheep (OX; n=10 858), Black Brown Mountain Sheep (BNP; n=10 964), Valais Black Nose Sheep (NN; n=14 371) and White Alpine Sheep (BA; n=32 169). The analyses included pedigree data from herd book animals born between 1996 and 2008. Ancestors were considered as far back as year of birth 1970. All data was analysed with common population genetic software tools. Within the studied time span the largest increase in mean inbreeding coefficient was found for the NN breed (5,9 → 9,3 %), followed by the OX breed (2,4 → 4,3 %), the BNP breed (2,4 → 3,8 %) and the BA breed (1,4 → 2,5 %). Although the rate of inbreeding within the mentioned period from 1996 to2008 fluctuated to some extent, all four breeds showed a general upward trend. This is accompanied by a general downward trend in effective population size. The White Alpine breed revealed the largest number of founder equivalents, effective ancestors and founder genome equivalents. Over the course of the years, all four breeds showed a downward trend for these three parameters, but the decline in the BA breed was found much more pronounced compared to the others. A further indicator of a declining genetic diversity is the marginal contribution of the most important ancestor. This parameter increased in all four breeds (NN 11,05 → 19,79 %; OX 7,67 → 11,27 %; BNP 4,45 → 5,19 %; BA 2,84 → 4,69 %) during the studied time span from 1996 to 2008. Our results suggest that, for the short term, targeted population management should be envisaged for the NN breed only. However, genetic diversity analyses on a regular basis are recommended for all breeds.