Genome-Wide Association Study for Milk Protein Content in Romanian Dual-Purpose Cattle

Milk protein levels significantly influence the economic value of dairy products and industrial processing efficiency for cheese manufacturing. Prior research has shown that genetic selection for specific milk components relies on conducting a milk protein content Genome-Wide Association Study (GWAS) to identify robust molecular markers across diverse bovine breeds. While major international dairy populations like Holstein have undergone extensive genomic mapping, local dual-purpose populations often lack detailed genetic characterization. These regional animals provide unique genetic reservoirs that might harbor distinct alleles for nutritional quality and environmental adaptation. Dual-purpose breeds like the Romanian Simmental are valued for providing both high-quality meat and nutrient-dense milk to local markets. Understanding the hereditary basis of protein synthesis in these specific animals is essential for modernizing regional breeding programs. This absence of evidence motivated the current investigation into the genomic architecture of Romanian cattle.

This investigation sought to identify Single Nucleotide Polymorphisms (SNPs) associated with protein percentage in Romanian Simmental and Romanian Brown populations. Researchers aimed to map specific loci that contribute to the phenotypic variation of this key economic trait within the Arad region. The study focused on characterizing the genetic landscape of dual-purpose animals maintained at the Research and Development Station for Bovine Arad. By analyzing these specific cohorts, the team intended to uncover candidate genes involved in bovine lactation and protein metabolism. The work also addressed the need for breed-specific genomic data to enhance local selection indices for dual-purpose performance. Scientists targeted the identification of markers that could differentiate high-protein producers from the rest of the herd. Establishing these associations provides a foundation for future marker-assisted selection strategies in Romanian livestock management.

The experimental cohort comprised 271 Romanian Simmental and 42 Romanian Brown cows selected for phenotypic consistency. Genomic analysis utilized 33,531 Single Nucleotide Polymorphisms (SNPs) after applying rigorous quality control filters to the raw genotype data. A linear regression model adjusted the protein percentage for confounding factors including breed, days in milk (DIM), season, year, and parity. To account for population stratification, the researchers incorporated the first five principal components as covariates in the statistical framework. The team established a genome-wide significance threshold of p < 5 × 10⁻⁸ and a nominal threshold of p < 1 × 10⁻⁴ for all associations. Quality control steps ensured that only high-quality genetic variants were included in the final association testing phase. Mapping of significant variants identified proximal candidate genes across six different bovine chromosomes to pinpoint functional regions.

The analysis revealed one SNP achieving a significance level of p < 2.98 × 10⁻⁵, alongside seven other variants exceeding the nominal threshold. Although no markers reached the strict genome-wide significance cutoff of 5 × 10⁻⁸, the strongest association appeared on chromosome 25. This primary signal (p = 9.56 × 10⁻⁶) was located near the C7orf61 gene, suggesting a potential regulatory role. On chromosome 13, the researchers identified KLF6, a gene previously linked to milk traits in Chinese Holstein populations. Another relevant candidate, AHCYL1, was mapped to chromosome 3 and is known for its role in calcium homeostasis during lactation. The seven nominal SNPs were distributed across six chromosomes, highlighting the complex genetic control of milk composition. These identified loci indicate a complex polygenic architecture for the protein trait in these specific Romanian breeds.

These findings offer preliminary insights into the genomic regions that regulate milk protein content in Romanian dual-purpose cattle. The identification of KLF6 and AHCYL1 suggests that certain conserved genetic mechanisms influence lactation across different bovine breeds. However, the authors emphasize that these initial associations require validation in larger independent cohorts to confirm their utility for selection. Future research should explore the functional impact of the C7orf61 region on protein synthesis pathways in mammary tissue. Integrating these markers into local breeding programs could eventually improve the nutritional profile of Romanian dairy products. Preservation of the unique genetic diversity found in dual-purpose breeds remains a priority for sustainable agricultural development. This study establishes a vital genomic baseline for the conservation and improvement of regional dual-purpose cattle populations.