Field investigation of bovine leukemia virus: env-based PCR detection and hematologic predictors in Korean dairy herds with productivity issues

초록

Importance: Enzootic bovine leukosis, caused by bovine leukemia virus (BLV), is associated with persistent lymphocytosis, lymphosarcoma development, and reduced herd productivity. In Korea, nationwide BLV prevalence data are limited, and its contribution to dairy herd problems remains unclear. Objective: To investigate prevalence of BLV and its association with hematological alterations in targeted dairy farms experiencing productivity issues in Korea. Methods: This study investigated five dairy farms reporting decreased milk yield, recurrent mastitis, poor conception rates, and delayed postpartum recovery. Eighty lactating cows underwent physical examination, body condition scoring, hematological and biochemical analyses, and polymerase chain reaction testing for BLV. Results: Overall BLV detection rate among these herds was 70% (56/80), with intra-herd positivity ranging from 57.1 to 90.0%. Lymphocytosis was observed in 31% of the cows. Multivariable generalized estimating equations analysis confirmed that higher lymphocyte counts were the strongest independent predictor of BLV status (adjusted odds ratio, 2.70; p = 0.005), demonstrating a robust association between hematological alterations and BLV positivity. Conclusions and Relevance: BLV infection is highly prevalent in the investigated Korean dairy farms with productivity problems. While these results may not represent the nationwide average due to selection bias, they emphasize the need for nationwide BLV surveillance and implementation of control measures in Korea.

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