PPP4R2 and mastitis: Among all the genes located in the candidate regions for mastitis resistance identified in the present study, several (DAB2, IDH1, NDUFS1, MRPL42, FYB, SOCS2, OSMR, RGMB, PPP4R2, EGFLAM and NUDT4) were highly expressed in both mammary gland and various immune cell lines as shown in Additional file 11: Figure S4.