Holstein steers (n = 40; initial BW = 84.9 ± 7.1 kg) were used to study the genesis of liver abscesses (LA) using an acidotic diet challenge with or without intraruminal bacterial inoculation. Steers were housed in individual pens inside a barn and randomly assigned to 1 of 3 treatments: 1) low-starch control diet comprised primarily of dry-rolled corn and wet corn gluten feed (CON); 2) high-starch acidotic diet with steam-flaked corn (AD); or 3) acidotic diet plus intraruminal inoculation with Fusobacterium necrophorum subsp. necrophorum (9.8 x 108 CFU/mL), Trueperella pyogenes (3.91 x 109CFU/mL), and Salmonella enterica serovar Lubbock (3.07 x 108CFU/mL), previously isolated from liver abscesses (ADB). Steers in AD and ADB were fed the acidotic diet for 3 d followed by 2 d of the CON diet, and this cycle was repeated four times. On d 23, ADB steers were intraruminally inoculated with the bacteria. At necropsy, gross pathology of livers, lungs, rumens, and colons was noted. Continuous data were analyzed via mixed models as repeated measures over time with individual steer as the experimental unit. Mixed models were also used to determine difference in prevalence of necropsy scores among treatments. Ruminal pH decreased in AD and ADB steers during each acidotic diet cycle (P ≤ 0.05). Liver abscess prevalence was 42.9% (6 of 14) in ADB vs. 0% in AD or CON treatments (P < 0.01). Ruminal damage was 51.1% greater in ADB than in AD (P ≤ 0.04). Culture of LA determined that 100% of the abscesses contained F. necrophorum subsp. necrophorum, 0% contained T. pyogenes, 50% contained Salmonella, and 50% contained a combination of F. necrophorum subsp. necrophorum and Salmonella. The F. necrophorum subsp. necrophorum was clonally identical to the strain used for the bacterial inoculation based on phylogenetic analysis of the whole genome. This experimental model successfully induced rumenitis and LA in Holstein steers and confirms the central dogma of LA pathogenesis that acidosis and rumenitis lead to the entry of F. necrophorum into the liver to cause abscesses. Our findings suggest that an acidotic diet, in conjunction with intraruminal bacterial inoculation, is a viable model to induce LA. Further research is needed to determine the repeatability of this model, and a major application of the model will be in evaluations of novel interventions to prevent LA.

中文翻译：

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使用酸中毒饮食挑战和细菌接种诱导荷斯坦牛肝脓肿实验模型的开发

荷斯坦公牛（n = 40；初始体重 = 84.9 ± 7.1 kg）用于通过酸中毒饮食挑战（有或没有瘤腔内细菌接种）来研究肝脓肿 (LA) 的起源。将小公牛圈养在谷仓内的各个围栏中，并随机分配到 3 种处理中的一种：1) 低淀粉对照饮食，主要由干玉米和湿玉米麸质饲料 (CON) 组成；2）含蒸汽压片玉米的高淀粉酸中毒饮食（AD）；或3)酸中毒饮食加上腔内接种坏死梭杆菌亚种。necrophorum (9.8 x 108 CFU/mL)、Trueperella pyogenes (3.91 x 109CFU/mL) 和沙门氏菌拉伯克血清型 (3.07 x 108CFU/mL)，先前从肝脓肿 (ADB) 中分离出来。AD 和 ADB 的公牛饲喂酸中毒饮食 3 天，然后饲喂 CON 饮食 2 天，这个循环重复四次。第 23 天，ADB 公牛瘤胃内接种细菌。尸检时，记录了肝脏、肺、瘤胃和结肠的大体病理学。通过混合模型分析连续数据，以个体转向为实验单位，随着时间的推移重复测量。混合模型也用于确定治疗之间尸检评分患病率的差异。在每个酸中毒饮食周期中，AD 和 ADB 阉牛的瘤胃 pH 值均下降 (P ≤ 0.05)。ADB 治疗组的肝脓肿患病率为 42.9%（14 例中的 6 例），而 AD 或 CON 治疗组的肝脓肿患病率为 0%（P < 0.01）。ADB 中的瘤胃损​​伤比 AD 中高 51.1% (P ≤ 0.04)。LA 培养确定 100% 的脓肿含有 F. necrophorum subsp.。其中，0% 含有化脓性密螺旋体，50% 含有沙门氏菌，50% 含有坏死球菌亚种的组合。necrophorum 和沙门氏菌。F. necrophorum subsp. 根据全基因组的系统发育分析，necrophorum 与用于细菌接种的菌株在克隆上相同。该实验模型成功诱导荷斯坦牛瘤胃炎和LA，证实了酸中毒和瘤胃炎导致坏死镰刀菌进入肝脏引起脓肿的LA发病机制的中心法则。我们的研究结果表明，酸中毒饮食与腔内细菌接种相结合是诱导 LA 的可行模型。需要进一步的研究来确定该模型的可重复性，该模型的主要应用将是评估预防 LA 的新型干预措施。