Background: Mastitis is a common infectious disease of the mammary gland and a major problem in the dairy industry. When cows affect mastitis, the number of somatic cells in their milk increases. It was reported that forebrain embryonic zinc finger-like (FEZL) encoding a stretch of 12 glycines (p.Gly105[12]) instead of 13 glycines (p.Gly105[13]) is associated with a lower somatic cell count, implicating the correlation between FEZL and mastitis resistance. Findings: To evaluate the impact of FEZL on mastitis incidence, a family with FEZL p.Gly105(12_13) polymorphism was generated via an embryo-transfer procedure. First embryos were recovered from cows inseminated with bulls homozygous for p.Gly105[12] and determined their sex. Based on transferring female embryos into recipient cows, 7 cows carrying the homozygous p.Gly105[12] and 5 cows carrying p.Gly105[12] and p.Gly105[13] were produced. These 12 cows with 15 cows of the same age and carrying the homozygous p.Gly105[13] were raised in the same station. After their deliveries via artificial insemination, milk yield and clinical mastitis were recorded during their first lactation period. Incidence of clinical mastitis was observed among cows carrying p.Gly105[12] significantly less than cows carrying the homozygous p.Gly105[13]. Moreover, affected cows carrying the homozygous p.Gly105[13] produced less milk with higher conductance than affected cows carrying p.Gly105[12], suggesting that cows carrying the homozygous p.Gly105[13] might suffer severer infection than cows carrying p.Gly105[12] because of their impaired immune response. Conclusions: The impact of FEZL on mastitis resistance was confirmed in a family with FEZL p.Gly105(12_13) polymorphism generated via an embryo-transfer procedure. Selection of cows carrying p.Gly105[12] could be beneficial in the dairy industry by reducing the incidence of mastitis.