<b>Supplementary Materials: </b><b>The Effects of Feeding a Simulated Waste Milk on Growth, Health, Fecal Microbiota, and Antibiotic Resistance in Dairy Heifer Calves.</b>

Feeding waste milk, a common practice in dairy farming, exposes calves to sub-therapeutic levels of antimicrobials, potentially contributing to antibiotic resistance—a growing concern globally. Many dairy farmers, including those in Ireland, continue this practice, feeding waste milk from antibiotic-treated cows to calves. While previous studies have linked waste milk feeding to changes in calf growth and health during the pre-weaning period, its effects post-weaning remain unclear.This study examined how the duration of antimicrobial exposure at levels equivalent to those found in waste milk influences health and growth outcomes of dairy heifer calves both pre- and post-weaning. It also assessed the prevalence of extended-spectrum β-lactamase (ESBL) resistant <i>Escherichia coli</i> in feces and changes in the fecal microbiota over time. To mimic waste milk, as derived from a cow treated with an intramammary suspension of antibiotics, a simulated waste milk (SWM) was prepared by adding amoxicillin (1.68 mg/L) and neomycin (2.28 mg/L) to a conventional milk replacer (MR).The study employed a randomized block design with 87 dairy heifer calves assigned to one of three treatments: (i) Long-term antibiotic (LTA), with calves fed SWM until weaning at 12 weeks; (ii) Short-term antibiotic (STA), with SWM fed from three to five weeks; and (iii) Control (CONT), with calves fed antibiotic-free MR. Calves were weighed weekly, and health scores, including fecal scores (tail and hindquarters cleanliness as diarrhea indicator), were recorded twice per week. Fecal and blood samples were collected to analyze microbiome changes, and the shedding of antimicrobial resistance, and. Blood samples were taken to measure systemic inflammation, using serum amyloid A as a biomarker.Results indicated that SWM feeding did not affect average daily gains pre- or post-weaning. However, higher fecal scores were observed in the LTA group during weaning and post-weaning in the STA group. Antibiotic-resistant isolates were present in all groups, with the highest prevalence in LTA. Fecal microbiota analysis revealed treatment-specific microbial community variations, with increased resistance genes in the bacteria <i>Enterococcus faecium</i> to macrolide, aminoglycoside, and tetracycline antibiotics in LTA and STA compared to CONT. In summary, SWM feeding did not significantly affect growth or overall health, it was associated with increased fecal shedding of resistant bacteria and some changes in the microbiota, indicating potential long-term implications for antimicrobial resistance in dairy herds.

饲喂废弃牛乳是奶牛养殖业中的常见操作，但该操作会使犊牛暴露于亚治疗剂量的抗菌药物中，可能加剧抗生素耐药性问题——这一问题已成为全球日益严峻的公共健康关切。包括爱尔兰在内的诸多奶牛养殖户仍在沿用该操作，将经抗生素治疗的母牛所产的废弃牛乳饲喂给犊牛。尽管既往研究已证实，饲喂废弃牛乳会改变犊牛断奶前的生长与健康状态，但该操作对犊牛断奶后的影响仍不明朗。本研究旨在探究与废弃牛乳中抗菌药物浓度相当的抗菌暴露时长，如何影响奶牛后备犊牛在断奶前后的健康与生长结局；同时还评估了粪便中超广谱β-内酰胺酶（extended-spectrum β-lactamase, ESBL）耐药性大肠杆菌（Escherichia coli）的携带率，以及粪便微生物群随时间的变化情况。为模拟经抗生素乳房内给药的母牛所产废弃牛乳，本研究在常规代乳粉（milk replacer, MR）中添加阿莫西林（1.68 mg/L）与新霉素（2.28 mg/L），制备得到模拟废弃牛乳（simulated waste milk, SWM）。本研究采用随机区组设计，将87头奶牛后备犊牛随机分为3组：① 长期抗菌暴露组（Long-term antibiotic, LTA）：犊牛全程饲喂SWM至12周龄断奶；② 短期抗菌暴露组（Short-term antibiotic, STA）：犊牛于3至5周龄期间饲喂SWM；③ 对照组（Control, CONT）：犊牛饲喂无抗生素代乳粉。研究人员每周对犊牛进行称重，每周两次记录犊牛健康评分，其中粪便评分以尾部与后躯清洁度作为腹泻严重程度的评判指标。采集粪便与血液样本以分析微生物组变化、抗菌耐药菌的排菌情况；同时以血清淀粉样蛋白A（serum amyloid A）作为生物标志物，检测血液样本以评估犊牛的全身炎症状态。研究结果显示，饲喂SWM对犊牛断奶前与断奶后的平均日增重均无显著影响。但长期抗菌暴露组在断奶期间的粪便评分更高，短期抗菌暴露组则在断奶后出现粪便评分升高的情况。所有组别均分离得到耐药菌株，其中长期抗菌暴露组的耐药菌株检出率最高。粪便微生物组分析结果显示，不同处理组的微生物群落结构存在组特异性差异：与对照组相比，长期与短期抗菌暴露组的粪肠球菌（Enterococcus faecium）中，大环内酯类、氨基糖苷类与四环素类抗生素的耐药基因丰度显著升高。综上，饲喂模拟废弃牛乳并未对犊牛的生长与整体健康状态造成显著影响，但该操作与耐药菌粪便排菌量升高及微生物组的部分改变相关，提示其可能对奶牛养殖群体的抗菌耐药性产生潜在的长期影响。

搜集汇总

背景与挑战

背景概述

该数据集提供了一项关于饲喂模拟废奶对奶牛犊影响的补充材料，研究了抗生素暴露对犊牛生长、健康、粪便微生物群和抗生素耐药性的影响。实验通过添加阿莫西林和新霉素模拟废奶，对比长期、短期饲喂组与对照组，发现生长未显著变化，但耐药细菌增加和微生物群发生特异性变化，揭示了潜在长期抗生素耐药风险。