Determination of the effects of PPARGC1 and OPN gene variants on milk yield in holstein cattle breed rai̇sed in Çukurova University

This thesis investigated the effects of polymorphisms in the PPARGC1A and OPN genes, which may affect milk yield and its components in the Holstein cattle population. The study aimed to identify genetic markers that could be used in genetic improvement programs by determining the relationships between SNPs in these genes and milk yield traits. Within the scope of this study, SNPs located at specific positions in the PPARGC1A and OPN genes were examined in the Holstein population. Two different genotypes (CC and CT) were detected at the 9th İntronikic 693636C>T position of the PPARGC1A gene. At the 5th İntron 5254G>T position of the OPN gene, two genotypes (GG and GT) were determined. The frequencies of genotypes and alleles were calculated, and the Hardy-Weinberg equilibrium was checked with the Chi-square test. Additionally, the 305-day total and daily milk yields were compared among genotypes. The frequency of the CC genotype in the PPARGC1A gene was 65% (0,65), and the frequency of the CT genotype was 35% (0,35). The C allele was found at 83% (0,83), and the T allele was found at a frequency of 17% (0,17). The Chi-square test result was calculated as 3,297, indicating that the population is in Hardy-Weinberg equilibrium. Statistical analyses showed that animals with the CC genotype had a higher 305-day total milk yield and daily milk yield than the CT genotype (p<0,05). In the OPN gene, the frequency of the GG genotype was 80% (0,80), and the frequency of the GT genotype was 20% (0,20). The G allele was found at a frequency of 90% (0,90), and the T allele was found at 10% (0,10). The Chi-square test result was calculated as 0,92, indicating that the population is in Hardy-Weinberg equilibrium. Regarding daily milk yield, animals with the GT genotype were found to have a higher milk yield than those with the GG genotype (p<0,05). These results revealed the significant effects of the polymorphisms detected in the PPARGC1A and OPN genes on milk yield. Positive effects of the C allele and CC genotype in the PPARGC1A gene on milk yield were observed. In the OPN gene, the positive effects of the G allele and GT genotype on daily milk yield were determined. These findings suggest that the use of PPARGC1A and OPN genotypes in genetic improvement programs could provide the potential for increasing milk yield.