Effect of Bovine Leukemia Virus Infection and Proviral Load on Health of Dairy Heifers through the Transition Period

The aim of the study was to evaluate the impact of Bovine Leukemia Virus (BLV) on the hematological, biochemical, and acute phase proteins in naturally infected dairy heifers through the transition period. Pregnant Holstein and Jersey heifers (n=24) were distributed into 2 experimental groups: (BLV+) and (BLV-), and BLV+ group was divided into two subgroups presenting high and low proviral load. Animals were assessed at weeks -3, -2, -1, parturition (0), +1, +2, +3 weeks. Blood samples were harvested for RBC, WBC, biochemical exams, including acute phase proteins biomarkers. Herd prevalence of serum positive animals for BLV was 57.25%, and 38.7% in pregnant heifers group. BLV has effect on hematological parameter, in addition to the increase of AST and high concentration of fibrinogen. Also, BLV+ heifers had high risk of inflammation according to the HP cut-off ≥ 2.0 mg/dL (OR= 4.959). Leukocyte counts from animals with high viral load were higher in the high viral load group (P=0.018), especially by lymphocytosis (P=0.036). This is the first publication presenting the impact of BLV on the health of dairy heifers through transition period, reporting a high risk of inflammation. Viral load can impact leukocyte counts, especially by predisposing lymphocytosis.