Smith Billy I, Fox Larry K, Aceto Helen W
Department of Clinical Studies - New Bolton Center, University of Pennsylvania, School of Veterinary Medicine, 382 West Street Road, Kennett Square, PA, 19348, USA.
Department of Veterinary Clinical Sciences, Washington State University College of Veterinary Medicine, PO Box 646610, Pullman, WA, 99164-6610, USA.
BMC Vet Res. 2025 Apr 7;21(1):251. doi: 10.1186/s12917-025-04699-8.
Mycoplasma bovis probably enters dairy herds when carrier animals are introduced. Comingled calves that become subclinical M. bovis carriers could promote cross-dairy transmission. A prospective cohort study in Holstein heifers from two unrelated herds (Farms A and B previously M. bovis positive and negative, respectively) comingled at a facility raising only their calves assessed: 1). prevalence of asymptomatic M. bovis infection; 2). associations between four anatomic sites (nares, eyes, ear canal, vagina; M. bovis culture with PCR confirmation). Fifteen calves per farm were enrolled every 4 months. Swabbing solutions were first collected at parent farms, thereafter monthly for 6 months, then quarterly to 21 months.
Three heifers from each dairy were lost after enrollment leaving 144 heifers (72 per farm) in the analysis. On day 1, a Farm A calf vaginal sample was the single M. bovis positive. While comingled, positives increased dramatically. Days of age to first positive were not different between farms (Farm A median = 109, range 42-561 days; Farm B median = 110, range 33-404 days; P = 0.96). Overall, 125/144 heifers yielded 634 positive samples, intranasal (46.7%), ocular (25.7%), vaginal (17.8%), ear canal (9.8%). The most common combinations were eye/nose (55/634, 43.3%) and nose/vagina (21/634, 16.5%). Intranasal positives increased exponentially at 2-3 months of age, plateauing over 4-10 months, and were more frequent than non-nose (Incidence Rate Ratio 1.44, 95% CI 1.41-1.47; P < 0.001). Positive combinations involving the nose temporally lagged the intranasal alone positives, but eventually reached similar frequencies. After returning to the parent farms, frequency of intranasal positives declined more rapidly than did non-nose.
M. bovis was cultured from all sites, but the nose appears most critical for transmission. Once intranasal carriage escalated, virtually all calves were subsequently positive at least once at one or more sites, indicating how readily asymptomatic M. bovis can disseminate in a population of animals and potentially manifest as clinical disease later in life.
当引入携带支原体的动物时，牛支原体可能会进入奶牛群。混养的犊牛若成为牛支原体亚临床携带者，可能会促进跨奶牛群传播。一项前瞻性队列研究对来自两个不相关牛群（A农场和B农场，此前分别为牛支原体阳性和阴性）的荷斯坦小母牛进行了研究，这些小母牛在一个仅饲养犊牛的设施中混养，评估了：1）无症状牛支原体感染的患病率；2）四个解剖部位（鼻孔、眼睛、耳道、阴道；通过PCR确认的牛支原体培养）之间的关联。每个农场每4个月招募15头犊牛。拭子样本首先在原农场采集，此后每月采集一次，持续6个月，然后每季度采集一次，直至21个月。
入组后，每个奶牛场有3头小母牛丢失，分析中留下144头小母牛（每个农场72头）。在第1天，A农场一头犊牛的阴道样本是唯一呈牛支原体阳性的样本。混养后，阳性样本数量急剧增加。各农场首次出现阳性的日龄无差异（A农场中位数 = 109天，范围42 - 561天；B农场中位数 = 110天，范围33 - 404天；P = 0.96）。总体而言，125/144头小母牛共产生634份阳性样本，其中鼻腔（46.7%）、眼部（25.7%）、阴道（17.8%）、耳道（9.8%）。最常见的组合是眼/鼻（55/634，43.3%）和鼻/阴道（21/634，16.5%）。鼻腔阳性在2 - 3月龄时呈指数增长，在4 - 10月龄时趋于平稳，且比非鼻腔部位更频繁（发病率比1.44，95%可信区间1.41 - 1.47；P < 0.001）。涉及鼻腔的阳性组合在时间上滞后于单纯鼻腔阳性，但最终频率相似。回到原农场后，鼻腔阳性的频率下降速度比非鼻腔部位更快。
在所有部位均培养出牛支原体，但鼻腔似乎对传播最为关键。一旦鼻腔携带率上升，几乎所有犊牛随后至少在一个或多个部位呈阳性一次，这表明无症状牛支原体在动物群体中传播得多么容易，并且可能在后期表现为临床疾病。
