Lack of evidence for association between the leptin/Sau3AI gene and milk yield traits in Holstein Friesian dairy cattle.

This study aimed to investigate the effect of leptin gene polymorphism and some environmental factors on milk production traits. Blood samples from 212 Holstein Friesian dairy cattle reared on a private farm were used. The intron 2 region of the leptin gene was digested with Sau3AI restriction enzyme using the PCR-RFLP method. A and B alleles and AA, AB, and BB genotype frequencies for the Sau3AI polymorphism were determined as 0.8821 and 0.1179, and 0.764, 0.236 and 0.000, respectively. Chi-square analysis revealed that the leptin gene polymorphism followed the Hardy-Weinberg equilibrium, including the absence of animals with the BB genotype. The effect of leptin gene polymorphism on all milk production traits was insignificant. For milk production traits, direct heritability (h_a²) varied between 0.03 ± 0.283 (for the dry period) and 0.50 ± 0.183 (for milk conductivity). Regarding the milking time (MT), the estimated breeding values (EBVs) of cattle with the AA genotype were higher than the AB genotype (P < 0.05). As a result of this study, in the selection program, allele or genotype could not be suggested as a marker for milk yield characteristics except for the possible exception of milking time and its relationship to mastitis incidence.