Dietary Bacteriophage on Growth Performance, Fecal microbiome, Diarrhea incidence, Nutrient Digestibility in Weaning Pigs = 이유자돈의 성장성적, 분변 내 미생물총, 영양소 소화율에 대한 사료 내 박테리오파지의 역할

다국어 초록 (Multilingual Abstract)

Lay summary
Weaning is a stressful stage for young pigs and is often associated with digestive problems such as diarrhea, which can impair growth and feed efficiency. These issues are commonly linked to harmful gut bacteria, including Escherichia coli, Salmonella, and Clostridium perfringens. Meanwhile, increasing restrictions on antibiotic use in many countries, including South Korea, have highlighted the need for safe and effective alternatives. This study examined whether dietary supplementation with a bacteriophage—viruses that specifically target harmful bacteria—could improve growth, digestion, and gut health in weaning pigs under normal conditions. A total of 160 weaning pigs were fed diets containing different levels of bacteriophages for five weeks. Pigs receiving bacteriophages showed improved growth, particularly during the later weaning period. Feed efficiency improved early after weaning without increased feed intake, indicating more efficient feed utilization. Nutrient digestibility tended to improve, and fecal moisture content decreased, suggesting firmer stools and a lower risk of diarrhea. While overall gut bacterial diversity remained unchanged, the microbial community structure shifted over time, with reductions in bacteria associated with gut imbalance and increases in beneficial bacteria at higher bacteriophage levels.
Overall, these findings indicate that dietary bacteriophages can support healthy growth and gut function in weaning pigs and represent a promising antibiotic-free strategy to help manage weaning-related digestive challenges.

Abstract
Weaning is one of the most challenging events in a pig’s life and is often associated with disturbances in intestinal integrity and immune function, which impair health status, growth performance, and feed intake (Campbell et al., 2013). During this period, weaning pigs commonly suffer from post-weaning diarrhea syndrome (PWD), a multifactorial condition characterized by impaired intestinal function (van Beers‐Schreurs, 1992; Gao et al., 2019; Eriksen et al., 2021).
The occurrence of PWD has been largely attributed to the presence and proliferation of enterotoxigenic Escherichia coli (ETEC), which is considered a primary causative agent (Eriksen et al., 2021; Rhouma et al., 2017; Luppi, 2017). In addition to ETEC, other microbial agents have been implicated in the onset and severity of PWD. Along with ETEC, Salmonella spp. are recognized as important pathogens affecting the health of weaning pigs and are associated with diarrheal disorders during the post-weaning period (Song et al., 2025). Furthermore, Clostridium perfringens, although a commensal member of the porcine gut microbiota, may contribute to intestinal disturbances and diarrhea under certain conditions.
Antibiotics have historically been employed in the livestock industry to control such pathogenic microorganisms. In particular, antibiotic growth promoters (AGPs), which involve the continuous inclusion of low-dose antibiotics in feed to improve growth performance, feed efficiency, and diarrhea incidence, have been widely used in swine production. However, prolonged antibiotic use has raised concerns regarding environmental contamination, antibiotic residues in livestock products, and the emergence of antimicrobial resistance (Zaheer et al., 2013; Saraiva et al., 2022). Consequently, the European Union initiated restrictions on AGPs with the ban of avoparcin in 1997 and implemented a complete prohibition on the use of antibiotics in animal feed by 2006, while South Korea banned the use of AGPs in 2011. Therefore, there is a need to develop alternative to antibiotics, which support growth performance in the absence of antibiotics.
Among various antibiotic alternatives, bacteriophages—viruses that infect and lyse bacteria—have gained increasing attention. In studies involving animals challenged with pathogenic infections, bacteriophage supplementation has been shown to exert therapeutic effects by reducing pathogen load and alleviating disease symptoms (Wall et al., 2010; Jamalludeen et al., 2009; Atterbury et al., 2009). In addition, Kim (2014) reported improved growth performance in unchallenged barrows supplemented with bacteriophages.
Nevertheless, despite these findings, the effects of bacteriophage supplementation under normal, unchallenged conditions remain unclear. For example, Han et al. (2016) reported that fecal concentrations of E. coli K99 did not differ significantly between phage-treated and untreated pigs throughout the sampling period (1, 3, and 7 d post-challenge; P > 0.05). These inconsistent results suggest that responses to bacteriophage supplementation may depend on animal health status and microbial pressure.
Therefore, the present study was conducted to evaluate the effects of dietary bacteriophage supplementation on growth performance and fecal microbiome in unchallenged pigs.

국문 초록 (Abstract)

이유자돈기는 돼지가 극심한 스트레스를 겪는 시기로, 설사와 같은 소화기 문제를 동반하는 경우가 많아 성장성적과 사료 효율이 저하될 수 있다. 이러한 문제는 Escherichia coli, Salmonella, Clostridium perfringens 등 유해한 장내 세균과 밀접한 관련이 있는데, 대한민국을 포함한 여러 국가에서 항생제 사용에 대한 규제가 강화되면서, 해당 균주를 효과적으로 억제할 수 있는 안전하고 효과적인 항생제 대체제 개발의 필요성이 커지고 있다.
본 연구에서는 전기 2주, 후기 3주, 총 5주에 걸쳐 전체 160두의 이유자돈을 대상으로 이유자돈 사료 내 박테리오파지의 수준별 첨가가 성장, 소화능력 및 장 건강에 미치는 영향을 평가하였다. 자돈들은 4개 처리구, 5반복, 반복당 8두씩 완전임의배치 되었으며, 처리구별 박테리오파지 수준은 각각 0%, 0.05%, 0.1%, 0.15% 였다.
그 결과, 사료내 박테리오파지의 수준이 증가함에 따라 이유 초기 사료효율이 개선되고 이유 후기 일당 증체량과 최종 체중이 향상되었다. 또한 건물의 소화율이 개선되고, 분변내 수분 함량이 감소하는 경향을 보였는데, 이는 박테리오파지가 이유자돈의 설사를 개선할 수 있음을 시사한다. 분변 내 미생물의 전체적인 다양성은 모든 처리구에서 유지되었으나, 미생물 군집은 시간 경과에 따라 변화하였으며, 박테리오파지 0.15% 처리구에서 장내 불균형과 관련된 세균은 감소하고 유익균은 증가하였다.
종합하면, 박테리오파지의 사료 내 첨가는 이유자돈의 성장과 장 기능을 개선하는 데 기여할 수 있으며, 이유자돈기 소화 장애를 관리하기 위한 유망한 항생제 대체제로 활용될 가능성을 시사한다.

목차 (Table of Contents)

• 1. Post-weaning diarrhea syndrome (PWD) 3
• 1.1. Physiology of weaning pigs 3
• 1.2. Major pathogens involved in PWD 4
• 1.2.1. Escherichia coli 4
• 1.2.2. Salmonella spp. . 5
• 1.2.3. Clostridium perfringens. 6
• 2. History of antibiotics use in a livestock industry 6
• 2.1. Antibiotic growth promoters (AGPs) 7
• 2.2. Emergence of antimicrobial resistance and regulatory bans 7
• 3. Alternatives to antibiotics 9
• 3.1. Probiotics 9
• 3.2. Antimicrobial peptides (AMPs) 9
• 3.3. Organic acids 10
• 3.4. Overview and limitations of antibiotic alternatives 10
• 4. Bacteriophage as alternatives to antibiotics 11
• 4.1. Life cycle of bacteriophage 13
• 4.1.1. The lysogenic cycle of bacteriophage 13
• 4.1.1. The lytic cycle of bacteriophage 13
• 4.2. Effects of dietary bacteriophage supplementation 14
• 4.2.1. Effects on growth performance 14
• 4.2.2. Effects on gut microbiome and nutrient digestibility 15
• 4.3. Bacterioiphage resistance mechanisms of bacteria 16
• III. Effects of varying levels of dietary bacteriophage on growth performance, nutrient digestibility, fecal microbiome, diarrhea incidence in weaning pigs
• Abstract 18
• Introduction 20
• Materials and Methods 22
• Results 26
• Discussion 28
• Conclusion 32
• IV. Literature Cited 43
• V. Summary in Korean 49