Abstract Irrational usage of antibiotic feed additives in livestock industry, especially as growth promoters, has become a global challenge due to the unintended zoonotic impact through resistance transfer. Herbal plant extracts or their secondary metabolites with antimicrobial properties may possess similar effects of various antibiotic feed additives in impeding the pathogenic microbial growth and enhancing the health, growth, and production performance. Majority of the calf-plant extract associated research works were primarily geared towards phenolic compounds and essential oils, with a few related to terpenes, saponins, tannins, flavonoids, organic acids, complex carbohydrates, and non-protein amino acids. The plant secondary metabolites possess diverse antimicrobial mechanisms, including cell membrane disruption, enzyme inhibition, substrate deprivation, and prevention of bacterial colonization, to name a few. Further, the unification of different levels and types of plant metabolites before supplementing to calves renders synergistic effects, which aids in several beneficial responses such as increased bioavailability, improved efficiency, and reduced undesirable effects and effective dosage. Nevertheless, the employment of herbal extracts or plant metabolites as antimicrobial feed additives to calves retain many challenges regarding the dosages, levels, adaptation lengths, herbal or herb-drug interactions, analytical methods, and public health safety. The present review focuses on assembling existing data on the plant-based antimicrobial components, individual secondary plant metabolites or plant extracts, which are already in use or having the efficacy in benefitting calves on supplementation.

中文翻译：

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植物次生代谢物作为犊牛饲料添加剂用于抗菌管理

摘要 抗生素饲料添加剂在畜牧业中的不合理使用，特别是作为生长促进剂，由于耐药性转移产生的意外人畜共患病影响已成为全球性挑战。具有抗菌特性的草本植物提取物或其次生代谢物在阻止病原微生物生长和提高健康、生长和生产性能方面可能具有与各种抗生素饲料添加剂相似的作用。大多数与小牛植物提取物相关的研究工作主要针对酚类化合物和精油，少数涉及萜烯、皂苷、单宁、黄酮类化合物、有机酸、复合碳水化合物和非蛋白质氨基酸。植物次生代谢产物具有多种抗菌机制，包括细胞膜破坏、酶抑制、基质剥夺和防止细菌定植，仅举几例。此外，在补充给小牛之前统一不同水平和类型的植物代谢物会产生协同效应，这有助于一些有益的反应，例如增加生物利用度、提高效率、减少不良影响和有效剂量。然而，将草药提取物或植物代谢物用作小牛的抗菌饲料添加剂在剂量、水平、适应时间、草药或草药-药物相互作用、分析方法和公共卫生安全方面仍存在许多挑战。本综述的重点是收集关于基于植物的抗菌成分、个别次生植物代谢物或植物提取物的现有数据，