Measurement of proviral load associated with the development of lymphocytosis in bovine leukaemia virus‐infected Holstein cattle at a dairy farm in Japan

Abstract

AbstractWe monitored the bovine leukaemia virus (BLV) proviral load (PVL) in peripheral blood lymphocytes (PBLs) and the PBL counts in BLV‐infected cattle on a dairy farm in Japan to determine the changes in PVL with the progression of lymphocytosis. A total of 25 BLV‐infected Holstein cattle at a dairy farm were followed up from May 2015 (0 month) to April 2016 (11 months). PBL counts and PVL were measured three times in 25 cattle. Based on their PBL counts, five cattle with normal PBL (≤7500 cells/µL) at 0 month but high PBL (>7500 cells/µL) at 11 months were classified as the increased group. All cattle in the increased group showed increased PVL compared to asymptomatic aleukaemic carriers at 11 months. This study revealed increases in PVL with the progression of lymphocytosis, suggesting that cattle with progression of lymphocytosis should be segregated from BLV‐negative cattle as soon as possible.