CAST gene is a candidate marker that influences the intensity of growth and meat quality. The aim of this study was to investigate the genetic variability of CAST gene in five Bulgarian sheep breeds – two merino, two local and one for milk. A total of 150 ewes, belonging to these breeds were investigated for polymorphisms of CAST gene by using PCR-RFLP method. A 622 bp fragment of Ovis aries CAST gene was amplified using PCR. After restriction with endonuclease MspI two alleles were observed in Ascanian, Caucasian, Breznik and Pleven Blackhead breeds. One allele (M) and one genotype (MM) were detected in Cooper-Red Shumen breed. The highest frequency of the allele N was established in the Ascanian merino breed (0.27) followed by Caucasian merino (0.13), Breznik (0.12) and Pleven Blackhead (0.07). Two genotypes - MM and MN, were observed in Caucasian, Breznik and Pleven Blackhead breeds. The three possible genotypes were found only in Ascanian merino ewes - MM, MN and NN. The lowest frequency of the homozygous genotype MM (0.50) and the highest frequency of the heterozygous genotype MN was established in the Ascanian merino breed (0.47). The obtained results confirm that the PCR-RFLP method can be used to identify different genotypic variation of CAST gene in Bulgarian sheep breeds. The established genetic diversity in the calpastatin gene indicates that, after further associative studies, this gene may be included in the breeding programs of certain sheep breeds.

Karnobat sheep plays an important role in the development of sheep breeding in Southeastern region of Bulgaria. They are valuable source of genetic material. The aim of present experiment was to determine the allele variation of CAST gene in Local Karnobat and Karnobat Merino sheep breeds. A total of 60 blood samples were collected – 30 per breed. DNA was extracted and genotypes of all animals were identified by means of PCR-RFLP technique. The restriction reactions were accomplished by specific enzyme MspI. As expected both breeds were characterized with low level of genetic diversity due to the fact that mostly maintaining selection has been implemented. In Local Karnobat sheep breed was identified only one heterozygous individual from all 30. In Karnobat merino were identified allele M with frequency 0,97 and allele N with frequency 0,03. Genotypes MM and MN were revealed with frequencies 0,93 and 0,07, respectively. According to the statistical analysis both breeds were in HWE equilibrium.

This study aimed to investigate the genetic polymorphisms in Agouti signaling protein (ASIP) and melanocortin 1 receptor (MC1R) genes and their association with coat color in native Bulgarian sheep breeds. A total of 247 individuals belonging to 7 native sheep breeds from 38 herds were genotyped for the ASIP and MC1R genes. Five single nucleotide polymorphisms (SNPs) were de-tected in the MC1R gene and three haplotypes representing MC1R ED and E+ alleles were identified among the studied sheep breeds. It was found that the dominant ED allele of MC1R is absent in the breeds - Patch-faced Maritza and Dubenska. The most common haplotype (h3) of the domi-nant ED allele was associated with either black or brown coat color in native Karnobatska, Kara-kachanska and Cupper-red Shumenska breeds, respectively. We can infer that haplotype 3 alleles could be a possible result that could interpret the mechanisms of black wool colour manifestation in the native Karnobatska sheep breed, which has formed the genetic pool of this sheep breed.