Abstract :
Genetic diversity studies in domestic animals aim at evaluating genetic variation within
and across breeds mainly for conservation purposes. In Sicily, dairy sheep production represents
an important resource for hilly and mountain areas economy. Their milk is used for
the production of traditional raw milk cheeses, sometimes protected designation of origin
(PDO) cheeses. In some cases, the quality of these products is linked to a specific breed,
i.e. mono-breed labelled cheeses and it is therefore important to be able to distinguish
the milk of a breed from that of others, in order to guarantee both the consumer and the
breed itself. In order to investigate the genetic structure and to perform an assignment
test, a total of 331 individuals (Barbaresca, BAR n = 57, Comisana, COM n = 65, Pinzirita, PIN
n = 75, Sarda, SAR n = 64, and Valle del Belice, VDB n = 70) were analysed using a panel of
20 microsatellite markers. A total of 259 alleles were observed with average polymorphic
information content equal to 0.76, showing that the microsatellites panel used was highly
informative. Estimates of observed heterozygosity ranged from 0.65 in the BAR breed to
0.75 in the COM breed. The low value of genetic differentiation among breeds (Fst = 0.049)
may indicate that these breeds are little differentiated probably due to common history and
breeding practices. The low Fis and Fit values indicated low level of inbreeding within and
among breeds. The unrooted neighbor-joining dendrogram obtained from the Reynold’s
genetic distances, and factorial correspondence analysis revealed a separation between
BAR and the other sheep breeds. Recent migration rates were estimated, showing that four
out of the five breeds have not received a significant proportion of migrants. Only for the PIN
breed a recent introgression rate from the VDB breed (7.2%) was observed. The Bayesian
assignment test showed that BAR and SAR breeds had a more definite genetic structure
(proportion of assignment of 92% and 86.6%, respectively), whereas the lowest assignment
value was found in the PIN breed (67.1%). Our results indicated high genetic variability,
low inbreeding and low genetic differentiation, except for BAR breed, and were in accordance
with geographical location, history, and breeding practices. The low robustness of
the assignment test makes it unfeasible for traceability purposes, due to the high level of
admixture, in particular for COM, PIN and VDB.
