Experimental infection of cows during pregnancy has also been found to result in seropositive calves at birth, indicating that calves had been infected (56). 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 contamination in dairy herds. culture (1). The etiological agent of EBL is usually bovine leukemia virus (BLV), an oncogenic retrovirus member of the genus (family or during delivery. infections under field conditions have been exhibited by testing newborn calves before colostrum feeding, and proved to be between 4 and 18% (51C55). This natural BLV infection has been found to be independent of the breed (52, 53), dam age, dam parity, and time of BLV contamination in the dam (42), but has been associated with maternal lymphocytosis (54, 55), malignant lymphoma (54), and maternal viral loads (52). Experimental contamination of cows during pregnancy has also been found to result in seropositive calves at birth, indicating that calves had been infected (56). Recently, Sajiki et al. (57) reported the direct evidence of Cholic acid intrauterine contamination in two pregnant dams with a high proviral load (PVL). These authors detected BLV DNA in both of the newborns delivered via cesarean section by nested PCR, and found that the amplified BLV-gene sequences from the dams and the newborns were completely identical. These authors also detected BLV provirus in placental and cord blood, but not in amniotic fluid, suggesting that placental and cord blood might be routes of vertical BLV transmission. (52) investigated the frequency of perinatal BLV contamination in field conditions in Japan and observed that 10 out of 129 (7.7%) calves born from BLV-infected cows were infected in the birth canal, and 14 (10.8%) were infected transmission is significantly correlated with the maternal viral load. Therefore, selecting breeding cows according to their viral loads could reduce the Cholic acid number of intrauterine infections. In addition, considering that BLV can also be transmitted Cholic acid through the birth canal, cesarean section in dams with high PVL should be aseptically conducted to minimize the risk of BLV transmission to newborn calves. Ideally, heifers should be separated from adult cows with high rates of infection before the calving process and newborn calves should be removed from their dams at birth and placed in a clean dry area to be fed good-quality colostrum during their first 12 h of life. Additionally, calves born infected should be identified as soon as possible and segregated from the herd. Some of these management practices are included in control programmes based on test and segregate, and have been useful to decrease prevalence or even achieve eradication of the disease (33, 47, 71). Preventive strategies when feeding calves with colostrum and milk Colostrum is the main source of nutrients and maternal immunoglobulins for the newborn calf. The timely feeding of high-quality and adequate Cholic acid volumes of uncontaminated colostrum is usually a key factor, essential to the health and survival of neonatal dairy calves (72). Since the incidence of BLV contamination in dairy CSF2RB herds is usually high, natural suckling from dams should be avoided and replaced by artificial feeding with either a high-quality colostrum bank or colostrum replacer. The high-quality colostrum bank could be obtained as pooled colostrum from BLV-negative dams. However, in dairy herds with high rates of infection, this would be almost impossible to conceive. In this case, a.