An 8-year longitudinal sero-epidemiological study of bovine leukaemia virus (BLV) infection in dairy cattle in Turkey and analysis of risk factors associated with BLV seropositivity

Enzootic bovine leukosis (EBL) which is caused by bovine leukaemia virus (BLV) has an important economic impact on dairy herds due to reduced milk production and restrictions on livestock exports. This study was conducted to determine the BLV infection status in Central Anatolia Region of Turkey, an important milk production centre, and to examine the risk factors such as purchasing cattle, increasing cattle age, cattle breed and herd size associated with transmission of BLV infection. To estimate the rate of BLV infection, a survey for specific antibodies in 28,982 serum samples from animals belonging to 1116 different herds situated in Central Anatolia Region of Turkey were tested from January 2006 to December 2013. A generalized mixed linear model was used to evaluate the risk factors that influenced BLV seroprevalence. Antibodies against BLV were detected in 431 (2.28 %) of 18,822 Holstein and 29 (0.28 %) of 10,160 Brown Swiss cows. Among 1116 herds, 132 herds (11.82 %) had one or more positive animals. Also results of our study show that the prevalence of BLV infection increased from 2006 to 2011, and it tends to reduce with BLV control programme. Furthermore, we found positive associations between percentage of seropositive animal and increasing cattle age, herd size, cattle breed and purchased cattle. Age-specific prevalence showed that BLV prevalence increased with age. These factors should be taken into consideration for control of BLV infection.