Abstract :
Italy has a long history of sheep breeding and, despite a dramatic number contraction
occurred in the last century, still counts several local sheep breeds that may represent a
unique source of genetic diversity. Here we present the results from the genetic characterization
of seven Italian dairy sheep breeds by 19 STR markers. High levels of polymorphism
were generally detected, with 16.2 average alleles per locus and an average gene diversity
of 0.79. The within-breed analysis highlighted, in six out of the seven breeds, a remarkable
proportion of loci displaying significant heterozygote deficit. Moreover, within-breed
percentages of locus pairs with significant genotypic disequilibrium were, for all breeds,
markedly higher than expected by chance thus suggesting the presence of population stratification.
The subdivision was particularly evident for the Leccese sheep breed and was
confirmed by the STRUCTURE analysis. On the contrary, results generally highlighted Sarda
as the most homogeneous, but less inbred, population, consistently with its large census size
and longstanding effective genetic management practices. Both STRUCTURE analysis and
measures of genetic distance, with the exception of those based on allele sharing, suggested
the presence of a phylogeographic gradient, with Sarda as the most differentiated breed
and continental breeds from the same region tending to group closer to each other.Taken
together, the results highlighted that all the Italian breeds display a genetic variability
content comparable to other European breeds, thus demonstrating their importance as
genetic reservoir for future selection options. However, management actions should be
more effectively implemented in local endangered breeds in order to reduce inbreeding
and within-breed sub-structuring.
