Three novel single-nucleotide polymorphisms of MBL1 gene in Chinese native cattle and their associations with milk performance traits

Mannan-binding lectin (MBL), a pattern recognizing serum protein, participates in the innate immune system of mammals as an opsonin. In humans, single-nucleotide polymorphisms (SNPs) in MBL2 gene were found to cause various innate immune dysfunctions. In the present study, we discovered three single-nucleotide polymorphisms of the MBL1 gene in Chinese native cattle and analyzed their associations with milk traits. By screening the genetic variation of MBL1 in 1053 individuals of three Chinese native cattle breeds including China Holstein, Luxi Yellow and Bohai Black using created restriction site–polymerase chain reaction (CRS–PCR), PCR–restriction fragment length polymorphism (PCR–RFLP) and DNA sequencing techniques, three new SNPs, g.855G>A, g.2651G>A and g.2686T>C, were found to have allele frequencies of 0–12.65%, 24.07–42.39% and 56.95–73.68%, respectively. While SNP g.855G>A is located within intron І, the other two SNPs reside in the exon II region with one mutation being non-synonymous (GTT (Val) > ATT (Ile)) and the other synonymous (GCT (Ala) > GCC (Ala)). Among the 596 Chinese Holstein cattle with at least 3 lactation Dairy Herd Improvement (DHI) records, eight different haplotypes and 19 genotype combinations were detected. Statistical analyses revealed no correlation between either g.855G>A or g.2686T>C and somatic cell score (SCS), however significant association was found between g.2651G>A and SCS, suggesting a possible role of this SNP in the host response against mastitis. Our data also suggested that the combined genotypes of GGC/AAC with the lowest SCS, AAT/AAT with the highest protein content and AGC/AGC with the highest 305-d milk yield were favorable combinations for mastitis resistance and milk production traits. Therefore, GGC/AAC, AAT/AAT and AGC/AGC can be used as possible candidates for marker-assisted selection in the dairy cattle breeding program.