Evaluation of total white blood cell count as a marker for proviral load of bovine leukemiavirus in dairy cattle from herds with a high seroprevalence of antibodies against bovine leukemia virus

Abstract

Objective: To determine the normal reference interval for white blood cell (WBC) counts in dairy Holstein cows in Argentina and to analyze the correlation of total WBC counts and blood proviral load (PVL) in Bovine leukemia virus (BLV)-infected animals, with the final purpose to identify a hematological marker that can estimate the level of in vivo infection. Animals ? A total of 307 lactating cows from 16 dairy herds with high BLV seroprevalence. Procedure ? Blood samples were used for manual determination of WBC count, BLV p24 antibodies by ELISA, and PVL by real-time PCR. Results ? The normal reference interval of WBC for BLV-negative dairy cows was stated as 2153-11493 cells/ul. In the herd used to analyze the correlation between WBC count and PVL, 73% of the animals showed normal values of WBC counts. Of them, only 19.6% showed high PVL. Most of the animals with high WBC counts (35/39) showed high PVL. The mean WBC count was significantly higher among the animals with high PVL than among those with low or undetectable PVL (P<0.0001). A significant correlation was found between WBC counts and PVL (rho = 0.71; P<0.0001). Conclusions and Clinical Relevance ? This work updates the reference interval for WBC counts in Holstein cows from highly BLV-infected herds. It also represents the first study that shows that the WBC count is correlated with PVL in dairy cattle under natural conditions. The WBC count could thus be a potential tool to select and monitor the BLV level of infection towards the rational control of transmission.