Investigating the genetic component of fatty acid content in sheep milk

The fatty acid (FA) profile of milk fat may affect the nutritional and market value of sheep dairy products. In this study we present repeatability estimates and results of quantitative trait loci (QTL) detection analyses for FA profile of sheep milk obtained by a genome scan approach applied to an experimental Sardinian×Lacaune back-cross population. The experimental flock was constituted by 967 daughters of 10 F1 sires corresponding to a classical daughter design for QTL detection. Fatty acid contents were determined twice in the middle of 2nd (847 records) and 3rd lactation (795 records) by gas chromatography. Means, standard deviations as well as raw correlations were calculated for the 17 most abundant fatty acids, their sums and ratios, based on 1454 records from 727 ewes with two samplings. A repeated measurement model including, as a fixed effect, the year of production by management group interaction and the random effects of sire and animal within sire was applied to all the analysed variables. For each trait R2 statistics associated with the fixed part of the model, the sire and the animal within sire components of the total variation were estimated. The genotypes at 146 microsatellite markers spanning the 26 ovine autosomes were available. The individual solutions for the 727 ewes with two records were used as phenotypes for QTL analyses. An across-family single trait QTL analysis was carried out by within-family linear regression. Chromosome locations significant at least at the 5% chromosome-wise level were retained. The overall pattern of raw correlations showed that FA profile is a very complex system resulting from numerous inter-relationships between basic FA. The portion of variation absorbed by the fixed part of the model differed markedly across variables, as showed by R2 statistics which ranged from 11.3% to 78.3%. FA showed large variability in terms of repeatability estimates, which ranged between 14.1% for C18:3 and 57.3% for C4. The most repeatable FA were C4, C14:1 and C17. For almost all the analysed variables, significant genome locations were found. Only for C4 was no genome region affecting the trait variability identified. The highest number of significant locations was found for C14_1 and its ratio with C14. The most significant QTL were detected for C14 and C16 on OAR 11 and for monounsaturated FA (MUFA) on OAR 6. A total of 82 locations significant at least at the 5% chromosome-wise threshold were detected. The present study suggests that for fatty acid profile of sheep milk both classical quantitative genetic approach and genomic information based selection approaches will be realistic options in the future.