In the present study, although no significant differences (p > 0.05) were observed in the estimated Day 1 SAA and SAA slopes between cows with and without follicular cysts, the G allele of the FOXP3 variant may affect the function of T-reg cells, thereby affecting the different inflammation statuses between cows with and without follicular cysts and possibly with mastitis and days of open periods. This evidence concerns the gene FOXP3 and mastitis.