Hokkaido Higashi Agriculture Mutual Aid Association, 14-37-3 Tawarabashi, Nakashibetsu 086-1137, Japan; Veterinary Epidemiology Unit, Graduate School of Veterinary Medicine, Rakuno Gakuen University, 582 Bunkyodai Midorimachi, Ebetsu 069-8501, Japan.
Veterinary Epidemiology Unit, Graduate School of Veterinary Medicine, Rakuno Gakuen University, 582 Bunkyodai Midorimachi, Ebetsu 069-8501, Japan.
J Dairy Sci. 2023 Jan;106(1):576-588. doi: 10.3168/jds.2021-21722. Epub 2022 Nov 21.
Bovine leukemia virus (BLV), which causes enzootic bovine leukosis and immunosuppression, is widely prevalent on Japanese dairy farms. However, in the absence of a national eradication scheme with compensation programs, it is important to estimate BLV-associated economic losses to raise farmers' awareness. Mastitis (includes both clinical and subclinical) is a common disease in the dairy industry and the most common reason for culling. We hypothesized that immunosuppression due to BLV predisposes subclinical mastitis. A retrospective cohort study was conducted to trace Holstein cows at 9 commercial dairy farms in the Nemuro and Kushiro regions of Hokkaido Prefecture, Japan, where monitoring of BLV proviral load is routine. Information regarding Dairy Herd Improvement data, parity number, and delivery day was collected at each farm. Cows with no confirmed infection with BLV during lactation were defined as non-infected. Low-proviral-load and high-proviral-load (H-PVL) cows were defined as those in which proviral load was below and over 2,465 copies/50 ng of DNA, respectively, or 56,765 copies/10 cells, respectively, throughout the lactation period. Survival analysis was performed using the frailty model to estimate the hazard ratio of subclinical mastitis for BLV infection status using data from 1,034 dairy cows after adjusting for parity number and delivery season as confounding factors. Kaplan-Meier survivor curves demonstrated that half of the H-PVL cows developed subclinical mastitis within 52 d after calving. The hazard ratio of subclinical mastitis for H-PVL cows was 2.61 times higher than that of non-infected cows. In 2017, there were 264,443 clinical mastitis cases in Hokkaido. Using field and published data, annual economic losses were estimated using Monte Carlo simulation. The economic loss due to mastitis associated with BLV infection per H-PVL cow was $418.59 (¥43,952), with the annual economic loss in Hokkaido Prefecture due to mastitis caused by BLV infection estimated at $6,097,225 (¥640,208,633). In summary, H-PVL cows were more susceptible to subclinical mastitis than non-infected and low-proviral-load cows, and mastitis due to BLV infection was projected to cause significant economic losses.
牛白血病病毒（BLV）可引起地方性牛白血病和免疫抑制，在日本奶牛场广泛流行。然而，由于没有国家根除计划和补偿计划，估计 BLV 相关的经济损失对于提高农民的认识非常重要。乳腺炎（包括临床和亚临床）是奶牛业中常见的疾病，也是淘汰的最常见原因。我们假设 BLV 引起的免疫抑制使亚临床乳腺炎易于发生。对日本北海道根室和钏路地区的 9 个商业奶牛场的荷斯坦奶牛进行了回顾性队列研究，这些地区常规监测 BLV 前病毒载量。在每个农场收集了关于奶牛群改良数据、胎次数和分娩日的信息。哺乳期未确诊 BLV 感染的奶牛被定义为未感染。低前病毒载量和高前病毒载量（H-PVL）奶牛分别定义为整个泌乳期前病毒载量低于 2465 拷贝/50ngDNA 或高于 56765 拷贝/10 个细胞的奶牛。使用 frailty 模型进行生存分析，以估计 BLV 感染状态对亚临床乳腺炎的风险比，调整胎次数和分娩季节作为混杂因素后，使用 1034 头奶牛的数据进行分析。Kaplan-Meier 生存曲线表明，一半的 H-PVL 奶牛在产后 52d 内发生亚临床乳腺炎。H-PVL 奶牛发生亚临床乳腺炎的风险比未感染奶牛高 2.61 倍。2017 年，北海道有 264443 例临床乳腺炎病例。使用现场和已发表的数据，通过蒙特卡罗模拟估计年度经济损失。每头 H-PVL 奶牛因 BLV 感染引起的乳腺炎相关经济损失为 418.59 美元（¥43952），北海道因 BLV 感染引起的乳腺炎的年度经济损失估计为 609.7225 万美元（¥640208633）。综上所述，H-PVL 奶牛比未感染和低前病毒载量奶牛更容易发生亚临床乳腺炎，BLV 感染引起的乳腺炎预计会造成重大经济损失。
