Evaluating nursery pig responses to in-feed sub-therapeutic antibiotics

Antibiotics have been used for over 60 years by the swine industry to improve growth performance and feed efficiency. With rising concerns over antimicrobial resistance and government restrictions such as the Veterinary Feed Directive on usage of in-feed antibiotics, alternatives to feeding antibiotic growth promoters (AGPs) to nursery pigs are needed. However, the mechanism of action by which AGPs work is poorly understood. Thus, the objective of this study was to investigate the mechanisms of action by which AGPs increase nursery pig performance. Over two replicates, 24 weaned pigs (6.75 ± 0.75 kg body weight) were randomly allotted to either control (CON, n = 12) or sub-therapeutic antibiotic (sCTC, n = 12) treatments and housed individually. A 2-phase corn-soybean-based nursery diet was fed, with the sCTC diets containing 40 ppm feed-grade chlortetracycline. Individual pig average daily gain (ADG), average daily feed intake (ADFI), and gain to feed ratio (G:F) were calculated weekly for 5 weeks. Thereafter, all pigs were euthanized and necropsied for tissue collection. The overall performance data indicated that sCTC pigs had increased ADG (0.43 vs. 0.32 kg/d, P = 0.001) and ADFI (0.51 vs. 0.37 kg/d, P = 0.002) compared with CON pigs; however, G:F was not different as a result of dietary treatment (0.85 vs. 0.88, P = 0.617). Intestinal barrier permeability, ileal active nutrient transport, and cecal short chain fatty acid concentrations did not differ (P > 0.10) due to dietary treatment, however changes in several ileum mRNA transcripts suggest that inflammation may be reduced in sCTC pigs. Further, the changes observed in the proteomes of the ileum, colon, skeletal muscle, and liver suggest that the sub-therapeutic mode of action of AGPs may include post-absorptive changes and warrants further investigation.

养猪行业已使用抗生素超过60年，用以提升生长性能与饲料利用率。随着人们对抗菌素耐药性的担忧日益加剧，加之《兽用饲料指令》（Veterinary Feed Directive）等法规对饲用抗生素使用的限制，开发仔猪饲用抗生素生长促进剂（AGPs）的替代方案已迫在眉睫。然而，目前人们对AGPs的作用机制仍知之甚少。因此，本研究旨在探究AGPs提升保育猪生长性能的作用机制。
本研究设置2次重复试验，将24头初始体重为6.75±0.75 kg的断奶仔猪随机分为对照组（CON，n=12）与亚治疗剂量抗生素组（sCTC，n=12），并单栏饲养。试验采用两阶段玉米-大豆基础保育日粮，sCTC组日粮添加40 ppm饲用级金霉素。每周记录并计算仔猪的平均日增重（ADG）、平均日采食量（ADFI）及料重比（G:F），试验周期共5周。试验结束后，对所有仔猪实施安乐死并进行剖检，采集组织样本。
整体生长性能数据显示，与CON组仔猪相比，sCTC组仔猪的ADG（0.43 vs 0.32 kg/d，P=0.001）与ADFI（0.51 vs 0.37 kg/d，P=0.002）均显著提升，但日粮处理对料重比无显著影响（0.85 vs 0.88，P=0.617）。日粮处理对肠道屏障通透性、回肠主动营养转运及盲肠短链脂肪酸浓度均无显著影响（P>0.10）；但回肠部分mRNA转录本的表达变化提示，sCTC组仔猪的炎症反应可能有所缓解。此外，回肠、结肠、骨骼肌及肝脏的蛋白质组学分析结果显示，AGPs的亚治疗剂量作用机制可能涉及吸收后层面的生理变化，该结论有待进一步研究验证。