Saskatoon Colostrum Company Ltd. (SCCL), Mesa, AZ 85206.
Department of Animal Science, Michigan State University, East Lansing 48824.
J Dairy Sci. 2020 Dec;103(12):11723-11735. doi: 10.3168/jds.2019-18044. Epub 2020 Oct 23.
The primary objective of this randomized field study was to assess the effect of antibiotic therapy on health and growth of preweaned dairy calves diagnosed with naturally occurring respiratory disease, using respiratory scoring and portable lung ultrasound. A secondary objective was to determine whether treatment response depended on clinical presentation at the time of diagnosis. Holstein calves (n = 357) were enrolled at 3 to 6 d of age and followed until 52 d on 2 commercial dairies. Calves were examined twice weekly by blinded members of the research team. Clinical respiratory and ultrasonographic lung scores were assigned at each exam and used to classify the first detected respiratory disease event (BRD1) into upper respiratory tract disease (clinical, no significant consolidation); subclinical lobular pneumonia (not clinical, patchy consolidation ≥1 cm); clinical lobular pneumonia (clinical, patchy consolidation ≥1 cm); subclinical lobar pneumonia (not clinical, ≥1 lobe consolidated); and clinical lobar pneumonia (clinical, ≥1 lobe consolidated). At BRD1, calves were blocked by their respiratory disease status and randomized to receive an antibiotic (tulathromycin, 2.5 mg/kg subcutaneous) or placebo (sterile saline, equal volume subcutaneous). Multivariable linear and logistic regression analyses were used to model response to therapy. At BRD1 (n = 289), the distribution of diagnoses was 29% (upper respiratory tract disease), 43% (subclinical lobular pneumonia), 13% (clinical lobular pneumonia), 8% (subclinical lobar pneumonia), and 7% (clinical lobar pneumonia). Early antibiotic therapy limited progression of lung consolidation immediately following treatment, reduced the likelihood of requiring treatment within 7 d of BRD1, and improved growth and mortality before weaning. Despite receiving multiple doses of antibiotics after BRD1, calves treated with either antibiotic or placebo were equally likely to enter the weaning phase with pneumonia. Clinical presentation was associated with response to treatment for worsening of consolidation, early treatment failure, days to retreatment, and average daily gain. Overall, treatment was associated with short-term benefits, but more research is needed to develop treatment protocols that more effectively treat pneumonia and ensure that calves enter the weaning period with ultrasonographically clean lungs.
本随机现场研究的主要目的是使用呼吸评分和便携式肺部超声评估抗生素治疗对自然发生呼吸道疾病的未断奶奶牛犊牛的健康和生长的影响。次要目的是确定治疗反应是否取决于诊断时的临床表现。3 至 6 日龄的荷斯坦奶牛（n = 357）在 2 个商业奶牛场入组，并在 52 日龄前进行随访。研究团队的盲员成员每周对奶牛进行两次检查。每次检查时都会进行临床呼吸和超声肺部评分，并用于将首次发现的呼吸道疾病事件（BRD1）分类为上呼吸道疾病（临床，无明显实变）；亚临床小叶性肺炎（非临床，局灶性实变≥1cm）；临床小叶性肺炎（临床，局灶性实变≥1cm）；亚临床肺叶性肺炎（非临床，≥1 个肺叶实变）；和临床肺叶性肺炎（临床，≥1 个肺叶实变）。在 BRD1 时，根据呼吸疾病状态将牛分组，并随机接受抗生素（替米考星，2.5mg/kg 皮下注射）或安慰剂（等量无菌生理盐水，皮下注射）。使用多变量线性和逻辑回归分析来建立对治疗的反应模型。在 BRD1（n = 289）时，诊断的分布为 29%（上呼吸道疾病），43%（亚临床小叶性肺炎），13%（临床小叶性肺炎），8%（亚临床肺叶性肺炎）和 7%（临床肺叶性肺炎）。早期抗生素治疗可限制治疗后肺部实变的进展，降低 BRD1 后 7 天内需要治疗的可能性，并改善断奶前的生长和死亡率。尽管在 BRD1 后接受了多次抗生素治疗，但接受抗生素或安慰剂治疗的牛在进入断奶阶段时同样可能患有肺炎。临床表现在治疗反应方面与肺部实变的恶化、早期治疗失败、重新治疗的天数和平均日增重有关。总体而言，治疗具有短期益处，但需要更多的研究来制定更有效地治疗肺炎并确保牛在断奶期肺部超声干净的治疗方案。
