Data_Sheet_1_Dairy Cows Experimentally Infected With Bovine Leukemia Virus Showed an Increased Milk Production in Lactation Numbers 3–4: A 4-Year Longitudinal Study.docx

Bovine leukemia virus (BLV) is widespread in global cattle populations, but the effects of its infection on milk quantity and quality have not been clearly elucidated in animal models. In this study, 30 healthy first-lactation cows were selected from ≈2,988 cows in a BLV-free farm with the same criteria of parity, age, lactation number, as well as milk yield, SCS, and composition (fat, protein, and lactose). Subsequently, these cows were randomly assigned to the intervention (n = 15) or control (n = 15) group, and reared in different cowsheds. Cows in the intervention group were inoculated with 1 × phosphate-buffered solution (PBS) resuspended in peripheral blood mononuclear cells (PBMC) from a BLV-positive cow, while the controls were inoculated with the inactivated PBMC from the same individual. From June 2016 to July 2021, milk weight (kg) was automatically recorded by milk sensors, and milk SCS and composition were originated from monthly performed dairy herd improvement (DHI) testing. Fluorescence resonance energy transfer (FRET)–qPCR and ELISA showed that cows in the intervention group were successfully infected with BLV, while cows in the control group were free of BLV for the entire period. At 45 days post-inoculation (DPI), the numbers of whole blood cells (WBCs) (P = 0.010), lymphocytes (LYMs) (P = 0.002), and monocytes (MNCs) (P = 0.001) and the expression levels of IFN-γ (P = 0.013), IL-10 (P = 0.031), and IL-12p70 (P = 0.008) increased significantly in the BLV infected cows compared to the non-infected. In lactation numbers 2–4, the intervention group had significantly higher overall milk yield (P < 0.001), fat (P = 0.031), and protein (P = 0.050) than the control group, while milk SCS (P = 0.038) and lactose (P = 0.036) decreased significantly. Further analysis indicated that BLV infection was associated with increased milk yield at each lactation stage in lactation numbers 3–4 (P = 0.021 or P < 0.001), but not with SCS and milk composition. Together, this 4-year longitudinal study revealed that artificial inoculation of BLV increased the milk yield in cows in this BLV challenge model.

牛白血病病毒（Bovine leukemia virus, BLV）在全球牛群中广泛传播，但其感染对奶牛产奶量与奶品质的影响尚未在动物模型中得到明确阐明。本研究从约2988头无BLV感染的牛场奶牛中，按照胎次、年龄、泌乳次数、产奶量、体细胞评分（Somatic Cell Score, SCS）以及乳成分（脂肪、蛋白质和乳糖）的一致标准，筛选出30头健康初产奶牛。随后，将这些奶牛随机分为干预组（n=15）与对照组（n=15），并分置于不同牛舍饲养。干预组奶牛接种经1×磷酸盐缓冲液（phosphate-buffered solution, PBS）重悬的BLV阳性奶牛外周血单个核细胞（peripheral blood mononuclear cells, PBMC），对照组则接种来自同一供体的灭活PBMC。2016年6月至2021年7月期间，通过奶传感器自动记录奶牛的奶重（kg），并通过每月开展的奶牛群改良（Dairy Herd Improvement, DHI）检测获取乳体细胞评分与乳成分数据。荧光共振能量转移-定量PCR（fluorescence resonance energy transfer-qPCR, FRET-qPCR）与ELISA检测结果显示，干预组奶牛成功感染BLV，而对照组奶牛在整个试验周期内均未感染BLV。接种后45天（days post-inoculation, DPI），与未感染组相比，BLV感染组奶牛的全血细胞（whole blood cells, WBCs）数量（P=0.010）、淋巴细胞（lymphocytes, LYMs）数量（P=0.002）、单核细胞（monocytes, MNCs）数量（P=0.001）以及IFN-γ（P=0.013）、IL-10（P=0.031）与IL-12p70（P=0.008）的表达水平均显著升高。在第2至4泌乳期，干预组的总产奶量（P<0.001）、乳脂肪（P=0.031）与乳蛋白（P=0.050）均显著高于对照组，而乳体细胞评分（P=0.038）与乳糖含量（P=0.036）则显著降低。进一步分析表明，在第3至4泌乳期，BLV感染与各泌乳阶段的产奶量升高相关（P=0.021或P<0.001），但与体细胞评分及乳成分无显著关联。综上，这项为期4年的纵向研究证实，在本BLV攻毒模型中，人工接种BLV可提升奶牛的产奶量。