Comparative analysis of κ-casein expressions and dairy herd improvement indices in Chinese Holstein cows of diverse κ-casein genotypes and transcripts

κ-casein (κ-CN, CSN3) variants affect milk composition, processing, milk protein content and milk yield. Whether the CSN3 mutation affects the expression of its own genes, which in turn affects the casein content and milk production, is unknown. To address this question, we conducted an experiment on the effects of κ-CN genotypes and transcripts on κ-CN expression and DHI indices. Through PCR sequencing, PCR-RFLP, western blot and PCA analysis, the expression of κ-CN in the κ-CN BB genotype was significantly greater than that in AA genotype and AB genotype (P < 0.05). For the heterozygous κ-CN AB genotype, there was no significant difference in the expression level of κ-CN between transcript A and transcript B (P > 0.05). The κ-CN transcripts were more suitable than the κ-CN genotypes as classification indicators associated with dairy herd improvement (DHI) indices such as milk protein content and milk production. Therefore, κ-CN variants do affect the content of κ-CN in milk, but it cannot be confirmed that the content of the κ-CN B variant is definitely higher than the κ-CN A variant, nor can the difference law in milk protein content be confirmed. This phenomenon may be related to regulatory changes caused by in the non-coding region of κ-CN.