Mitochondrial DNA D-loop A/G Transition at Position 869 as a Reproductive Performance Indicator in Gir Cattle

Reproduction is a critical aspect of livestock production, with mitochondria playing a pivotal role in providing the necessary energy for this high-demanding process. Maternally inherited mitochondria are known to influence various cellular functions, including ATP production and apoptotic regulation, and possess their own genome, including the Displacement loop (D-loop). This study aims to explore the mitochondrial DNA (mtDNA) D-loop SNPs and their potential association with reproductive traits in Gir cattle, an indigenous breed. Two groups of animals were categorized based on their reproductive performance, with good performers demonstrating shorter calving intervals, gestation lengths, days open, and fewer services per conception. Total DNA was isolated from blood samples, and mtDNA D-loop sequences were obtained through Sanger sequencing, resulting in 29 haplotypes. Comparative analysis revealed that animals with poor reproductive performance exhibited a higher number of polymorphic sites, transition/transversion biases, and occurrences of insertions/deletions (INDELs) compared to the good performers. Specifically, good performers showed higher A/G and G/A substitutions, while poor performers exhibited higher T/A, C/A, A/T, G/T, and G/C substitutions. The A/G transition at Position 869 was significantly associated with poor reproductive performance, impacting secondary structure stability and likely affecting energy efficiency. Validation of these findings in a larger Gir cattle population and exploring mtDNA polymorphisms in coding regions may establish a maternal lineage-based biomarker for assessing reproductive efficiency in this indigenous breed. This study sheds light on the significance of mitochondrial genetic factors in shaping reproductive traits and offers insights into sustainable livestock production.