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The aim of this study was to compare the genetic structure and genetic diversity of two Bulgarian sheep breeds. A total of 41 individuals from a modern Bulgarian sheep population (Rhodopean Tsigai, RT) and 46 representatives of a local Bulgarian sheep population (Middle Rhodopean Sheep, MRS) were investigated based on 12 STR (short tandem repeat, also known as microsatellite) markers. In total, 121 alleles were found in the two populations using 12 microsatellite loci. The mean number of alleles, the effective number of alleles, and the polymorphism information content (PIC) values per loci were 10.08, 4.96, and 0.73, respectively. When comparing the allelic diversity across the populations, the highest Na was observed in the MRS breed (10.58 ± 0.87), while the value of this parameter in the RT breed was 9.58 ± 0.71. The largest genetic diversity was found at locus INRA005 with 14.5 alleles and the smallest polymorphism was noted for locus ETH152 with 5.5 alleles. The level of observed heterozygosity was in the range of 0.60 to 0.860. The expected heterozygosity level range was 0.62 to 0.87. When 12 microsatellite loci were compared, the INRA005 locus showed the highest level of genetic variability. Using Nei’s standard genetic distance, the observed genetic distance between the RT and MRS breeds was 0.103. Both sheep breeds demonstrated mixed genetic profiles based on the studied microsatellite markers. The clustering obtained by STRUCTURE analysis showed that the MRS breed is a more homogenous population, whereas the RT breed is more heterogenous.

The uniqueness of ruminant milk lipids is based on their high concentration of CLA. The purpose of our research was to find the CLA content in sheep milk and milk products manufactured from sheep milk. Proceeding from ancient Bulgarian traditions of developing mountain sheep breeding, milk from two groups of sheep for combined use during the pasture period (May-July) and three types of traditional milk products were studied. The CLA content in individual samples of sheep milk varied from 17.8 to 56.5 mg/g fat. We found that the milk of the Tsigay crosses contained a higher CLA content than the milk of the Karakachan crosses. A higher content of biologically important cis 9, trans 11 CLA isomer was found in the milk fat of the Tsigay crosses than in the Karakachan crosses (25.1 vs. 22.3 mg/g fat, respectively). The highest CLA concentrations in the milk products were found in white brined cheese (35.6 mg/g), followed by yoghurt (29.5 mg/g), and the lowest in yellow cheese (21.8 mg/g). In conclusion, the effect of individual and breeds' differences as well as that of the season on the CLA content in the sheep milk fat was found out.