PPBP and periventricular leukomalacia: The secretion of chemotactic protein NAP-2/CXCL7 in cows of the healthy group, the L-PVL group, and the H-PVL group was measured with the NAP2/CXCL7 ELISA kit to investigate the effect of different BLV PVL on the chemotactic function of PMN in cows (Figure 2A).