For intramammary 25(OH)D3 treatments, 100 μg of 25(OH)D3 was diluted in 10 mL of sterile PBS (Dulbecco’s PBS without calcium or magnesium; Hyclone, Logan, UT) supplemented with 10% fetal bovine serum as a carrier for 25(OH)D3 (characterized serum; Hyclone).