The immunosuppressive nature of bovine leukaemia
virus (BLV) infection is well documented and associated
production losses make it one of the most important
diseases of cattle, particularly in dairy cows. Any
management interventions should be informed by an
understanding of the herd-level and within-herd infection
prevalence and of risk factors for spread of infection. Costs
associated with blood tests have been a prohibitive factor in
routine monitoring in domestic herds.
A regional cross-sectional study was undertaken to estimate
herd-level prevalence of BLV infection in commercial dairy
herds and identify associated risk factors. Bulk tank milk
(BTM) from 185 dairy herds randomly selected from Limpopo,
North West, Mpumalanga, Gauteng and Free State provinces
was tested for BLV infection using an indirect enzyme-linked
immunosorbent assay (ELISA). A questionnaire was used
to collect data regarding management practices and herdspecific
factors. Logistic regression was used to assess factors
associated with herd seropositivity. Multiple linear regression was used to identify factors associated with the quantitative
outcome of the BTM ELISA (E quant), as a proxy for within-herd
prevalence of BLV infection.
Estimated herd-level prevalence was 96% (149/155; 95%CI
92-99%); it differed between provinces (P=0.001): 77%
(17/22) in Mpumalanga, 97% (34/35) in Gauteng and 100%
in North West (n=65), Free State (n=26) and Limpopo (n=3).
Questionnaire data were obtained from 125 herds. No
factors were significantly associated with herd BLV infection,
likely due to the small number of negative herds. Use of
communal calving camps, reuse of rectal gloves without
disinfection and use of artificial insemination in cows were
associated with higher E quant. Regular treatment against flies
was associated with lower E quant.
Infection with BLV is widespread amongst commercial dairy
herds in the northern part of South Africa. Various aspects of
herd management have been identified where interventions
can be made to control of the disease.
Poster presented at the University of Pretoria, Faculty of Veterinary Science Faculty Day, September 07, 2017, Pretoria, South Africa.