Abstract
Bovine leukemia virus (BLV) is the causative agent of enzootic bovine leukosis (EBL). Although efficient eradication programs have been successfully implemented in most European countries and Oceania, BLV infection rates are still high worldwide. BLV naturally infects cattle, inducing a persistent infection with diverse clinical outcomes. The virus infects lymphocytes and integrates a DNA intermediate as a provirus into the genome of the cells. Therefore, exposure to biological fluids contaminated with infected lymphocytes potentially spreads the virus. Vertical transmission may occur in utero or during delivery, and about 10% of calves born to BLV-infected dams are already infected at birth. Most frequently, transmission from dams to their offspring occurs through the ingestion of infected colostrum or milk. Therefore, although EBL is not a disease specific to the neonatal period, during this period the calves are at special risk of becoming infected, especially in dairy farms, where they ingest colostrum and/or raw milk either naturally or artificially. Calves infected during the first week of life could play an active role in early propagation of BLV to susceptible animals. This review discusses the main factors that contribute to neonatal BLV infection in dairy herds, as well as different approaches and management practices that could be implemented to reduce the risk of BLV transmission during this period, aiming to decrease BLV infection in dairy herds.
Highlights
This review discusses the main factors that contribute to neonatal Bovine leukemia virus (BLV) infection in dairy herds, as well as different approaches and management practices that could be implemented to reduce the risk of BLV transmission during this period, aiming to decrease BLV infection in dairy herds
Our studies have shown that the colostrum of individual cows shows different provirus/antibody profiles, and that consumption of colostrum with infected cells and a poor content of antibodies could play a critical role in BLV propagation during young age [59, 60]
enzootic bovine leukosis (EBL) is not considered an infectious disease causing abortions or neonatal mortality, special attention should be given to neonatal calves in dairy herds, especially in those with high prevalence of BLV infection
Summary
Enzootic bovine leukosis (EBL), called bovine lymphosarcoma or bovine leukemia, is an infectious disease naturally occurring in cattle. When analyzing the relationship between the level of BLV antibodies and the PVL in blood and milk of lactating cows under natural conditions, we found a negative correlation, suggesting that the consumption of raw milk containing provirus or free virus particles and low levels of antibodies could favor BLV transmission to calves [58]. All these findings suggest that the feeding management of young calves could greatly influence the risk of milk-borne transmission
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