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

Milk protein content represents a key economic trait in dairy production, yet the genetic architecture underlying this trait remains unexplored in Romanian dual-purpose cattle breeds. This study conducted a genome-wide association analysis for milk protein content in 313 Romanian Simmental (n = 271) and Romanian Brown (n = 42) cows belonging to the Research and Development Station for Bovine Arad, Romania. Following quality control, 33,531 SNPs were tested for association with protein percentage adjusted for other effects (breed, days in milk, season, year, parity) using linear regression with the first five principal components as covariates to control population stratification. Although no SNP reached genome-wide significance (p < 5 × 10^-8), one SNP achieved significance (p < 2.98 × 10^-5) and seven additional SNPs exceeded the nominal threshold (p < 1 × 10^-4) across six chromosomes. The strongest association (p = 9.56 × 10^-6) mapped to chromosome 25 near C7orf61. Biologically relevant candidate genes included KLF6 on chromosome 13, previously associated with milk traits in Chinese Holstein, and AHCYL1 on chromosome 3, involved in calcium homeostasis. These findings provide initial insights into genomic regions influencing milk protein content in Romanian dual-purpose cattle, though validation in larger cohorts needs to be carried out.