Lacombe Research and Development Centre, Agriculture and Agri-Food Canada, Lacombe, AB, Canada.
Faculty of Veterinary Medicine, University of Calgary, Calgary, AB, Canada; Feedlot Health Management Services, Okotoks, AB, Canada.
Vet Microbiol. 2018 Feb;214:140-147. doi: 10.1016/j.vetmic.2017.12.015. Epub 2017 Dec 22.
Beef cattle in North America that are deemed to be at high risk of developing bovine respiratory disease (BRD) are frequently administered a metaphylactic antibiotic injection to control the disease. Cattle may also receive in-feed antimicrobials to prevent specific diseases and ionophores to improve growth and feed efficiency. Presently, attempts to evaluate the effects that these medications have on antibiotic resistance in the bovine nasopharyngeal microbiota have been focused on culturable bacteria that are associated with BRD. Therefore, we assessed the effects of injectable antibiotics on the nasopharyngeal microbiota of commercial feedlot cattle in Alberta, Canada, through the first 60 d on feed. Although all cattle in the study were also receiving in-feed chlortetracycline and monensin, the administration of a single injection of either oxytetracycline or tulathromycin at feedlot placement altered the nasopharyngeal microbiota in comparison with the cattle receiving only in-feed antibiotics. Oxytetracycline significantly (P < 0.05) reduced the relative abundance of Mannheimia spp. from feedlot entry to exit (≥60 d) and both oxytetracycline and tulathromycin treated cattle had a significantly lower relative abundance of Mycoplasma spp. at feedlot exit compared with the in-feed antibiotic only group. The proportion of the tetracycline resistance gene tet(H) was significantly increased following oxytetracycline injection (P < 0.05). Oxytetracycline also reduced both the number of OTUs and the Shannon diversity index in the nasopharyngeal microbiota (P < 0.05). These results demonstrate that in feedlot cattle receiving subtherapeutic in-feed antimicrobials, the administration of a single injection of either oxytetracycline or tulathromycin resulted in measurable changes to the nasopharyngeal microbiota during the first 60 d following feedlot placement.
在北美的肉牛中，如果被认为有发生牛呼吸道疾病（BRD）的高风险，则通常会注射一种治疗性抗生素来控制疾病。牛也可能接受饲料中的抗生素以预防特定疾病和离子载体以提高生长和饲料效率。目前，评估这些药物对牛鼻咽喉微生物群中抗生素耐药性的影响的尝试集中在与 BRD 相关的可培养细菌上。因此，我们通过在饲料中最初的 60 天评估了注射用抗生素对加拿大艾伯塔省商业育肥场牛的鼻咽喉微生物群的影响。尽管研究中的所有牛也都在接受饲料中的金霉素和莫能菌素，但在育肥场安置时单次注射土霉素或替米考星与仅接受饲料中抗生素的牛相比，改变了鼻咽喉微生物群。土霉素显著（P<0.05）降低了从进入育肥场到离开（≥60 天）的曼海姆菌属的相对丰度，与仅接受饲料中抗生素的牛相比，土霉素和替米考星处理的牛在离开育肥场时的支原体属的相对丰度明显较低。在注射土霉素后，四环素耐药基因 tet(H)的比例显著增加（P<0.05）。土霉素还降低了鼻咽喉微生物群中的 OTU 数量和香农多样性指数（P<0.05）。这些结果表明，在接受亚治疗性饲料中抗生素的育肥牛中，在进入育肥场后的最初 60 天内，单次注射土霉素或替米考星都会导致鼻咽喉微生物群发生可测量的变化。
