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BackgroundBovine Leukemia Virus (BLV) produces disorders on the immune system in naturally infected animals, which may counteract the development of immunity after vaccination. The aim of this study was to investigate whether healthy and BLV infected cattle elicited similar humoral responses after foot and mouth disease (FMD) immunization. In a field study, 35 Holstein heifers were selected based on their BLV serological status and immunized with a single dose of a commercial bivalent oil-based FMD vaccine. Serum samples were collected at 0, 15, 60, 165 and 300 days post vaccination (dpv).ResultsTotal anti-A24/Cruzeiro antibodies, IgM, IgG1, IgG2 titers and avidity index of specific antibodies were determined by ELISA. Although only marginally significant differences were found between groups in terms of total antibodies, anti-FMD IgM and IgG1 titers were significantly lower in heifers infected with BLV at the 15 dpv (p < 0.01). Animals that became infected during the study did not show differences to the BLV negative group.ConclusionsCattle infected with BLV at the time of immunization may elicit a low-magnitude serological response to a commercial Foot-and-mouth disease vaccine.

BLV causes one of the most relevant viral diseases of dairy cattle although the most of the infected animals are asymptomatic. There are controversies regarding reproductive losses on infected herds. Our purpose was to evaluate the horizontal transmission of the virus in a group of Holstein heifers confined in a rearing system and to determine the impact of infection on reproductive performance. Three hundred eighty-nine animals were sampled and seroconversion was determined by ELISA. The occurrence of estrous behavior, number of services/pregnancy, conception rate, percentage of pregnant animals by artificial insemination and by bull service during two breeding periods (June-July and November-December 2012) were recorded. Herd BLV initial seroprevalence was 45% and annual conception rate was 39.8% (CI 30.5%-49%). During the 18 month time course two seroconversion peaks were detected. The first one happened during the admission period, most likely due to quarantine and intensive health management of the animals. The second peak occurred during the first gestational period. At the end of the study, 73.6% of the heifers were BLV seropositive and there was reduction of 27% in the herd conception rate in the second breeding period (p=0.005). In conclusion, BLV infection and reproductive performance were negatively associated and high seroconversion was observed during the gestational period.

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