Feed efficiency is an economically important trait in sheep farming, directly influencing productivity and profitability. As a complex quantitative trait, FE is regulated by multiple genes, including the mechanistic target of the rapamycin MTOR gene, which plays a key role in skeletal muscle development, metabolism, and body weight regulation.

This study aimed to investigate the relationship between MTOR gene expression levels and SNP genotypes in sheep with different FE values raised in Latvia. Blood samples were collected from 76 lambs at approximately 81 days of age and 92 lambs at around 150 days, across two intensive fattening groups. About 60% of the lambs represented the Latvian Dark-Head breed. Expression of the MTOR gene and 14 SNPs within the gene were analysed using comparative and correlation analyses.

The results showed that MTOR gene expression increased significantly after the fattening period, suggesting a rising demand for MTOR protein as muscle and body mass increase. In seven SNPs, significant differences in gene expression were observed between genotype groups. Additionally, eight SNPs showed potential associations with increased gene expression during intensive fattening. Statistically significant correlations were found between pre-fattening MTOR expression and the Kleiber ratio at 60 days, as well as between post-fattening expression and relative growth rate.

These findings suggest that MTOR gene expression and its associated SNP variants could serve as promising molecular markers in genetic selection for improved feed efficiency. This study provides new insights into the genetic regulation of growth and metabolism in Latvian sheep populations.

Acknowledgements: This research was supported by the Latvian Council of Science, Latvia, under projects LZP-2021/1-0489 and LZP-2024/1-0092.