Essential Oils as an Alternative to Antibiotics to Reduce the Incidence and Severity of Necrotic Enteritis in Broiler Chickens: A Short Review

Due to the removal of antibiotic growth promoters (AGPs) and consumer pressure for antibiotic-free (ABF) or no antibiotics ever (NAE) poultry production, there is a need for sustainable alternatives to prevent disease in commercial poultry operations. Without AGPs, there has been a rise in diseases that were traditionally controlled by subtherapeutic levels of antibiotics in the diet. This has impacted the health of commercial poultry and has been a significant cost to poultry producers. To mitigate this, the industry has started to investigate alternatives to antibiotics to treat these forthcoming health issues, such as necrotic enteritis (NE). NE is an enteric disease caused by an over proliferation of toxigenic Clostridium perfringens (CP) in the gastrointestinal tract. Although CP is a commensal in the avian intestinal tract, dysbiosis caused by inflammation and impaired intestinal integrity facilitates uncontrolled replication of CP. Infectious agents, such as Eimeria maxima, appear to be a predominant predisposing factor that promotes NE. However, non-infectious stressors, including dietary changes, have also been associated with NE to some degree. As a result of increased pressure to restrict the use of antibiotics, there is a need for research evaluating the efficacy of alternatives, such as plant-derived essential oils, as potential tools to mitigate NE in commercial poultry flocks. The aim of this study is to review the effects of essential oils as an alternative to antibiotics to reduce the incidence and severity of necrotic enteritis in broiler chickens.

Strategies to Reduce Antibiotic Use in Rabbit Production

Possible ways to reduce antibiotic use in rabbit production are discussed, based on a literature survey. Several management strategies have been proven to successfully reduce disease pressure in rabbit production. The primary way of reducing risk of disease is ＂all-in all-out＂ management, as it allows thorough cleaning and disinfection. A second tool is choosing reproduction stock with a minimal disease level. Animals with a near Specific-Pathogen-Free （SPF） status, or even entirely disease-free animals, lead to high-health-status farms where antibiotics are rarely used. To reduce the risk of enteritis, quantitative aspects in the early fattening stage are important, apart from some ,qualitative feed characteristics （especially the carbohydrate complex）. Finally, despite discussions about their effectiveness, pro/prebiotics and some other additives have shown some potential in reducing enteric problems. Alternatives to antibiotics are only useful, however, if the whole chain （reproduction stock producers, breeders, feed companies, slaughterhouses and even veterinarians） is convinced and forced into a globally consistent strategy. In the absence of such a consistent approach, both preventive and curative use of antibiotics remains the easiest and most inexpensive way to control disease in rabbit production.

The Bioprospecting of Microbial-Derived Antimicrobial Peptides for Sustainable Agriculture

Strategies aimed at defining,discovering,and developing alternatives to traditional antibiotics will underlie the development of sustainable agricultural systems.Among such strategies,antimicrobial peptides(AMPs)with broad-spectrum antimicrobial activity and multifaceted mechanisms of action are recognized as ideal alternatives in the post-antibiotic era.In particular,AMPs derived from microbes with active metabolisms that can adapt to a variety of extreme environments have long been sought after.Consequently,this review summarizes information on naturally occurring AMPs,including their biological activity,antimicrobial mechanisms,and the preparation of microbial-derived AMPs;it also outlines their applications and the challenges presented by their use in the agroindustry.By dissecting the research results on microbial-derived AMPs of previous generations,this study contributes valuable knowledge on the exploration and realization of the applications of AMPs in sustainable agriculture.

A comprehensive review on natural phenolic compounds as alternatives to in-feed antibiotics

Intensive livestock and poultry farming in China largely relied on the use of in-feed antibiotics until July 2020.The consequences of antibiotic overuse in animal feed include accumulation in animal products and the development of bacterial antibiotic resistance,both of which threaten food safety and human health.China has now completely banned the circulation of commercial feed containing growth-promoting drug additives(except Chinese herbal medicine).Therefore,alternatives to in-feed antibiotics in animal production are greatly needed.Natural phenolic compounds(NPCs)exist widely in plants and are non-toxic,nonpolluting,highly reproducible,and leave little residue.Many natural flavonoids,phenolic acids,lignans,and stilbenes have polyphenol chemical structures and exhibit great potential as alternatives to antibiotics.In this review we delineate the characteristics of plant-derived NPCs and summarize their current applications as alternatives to in-feed antibiotics,aiming to provide new strategies for antibiotic-free feeding and promote the development of more sustainable animal husbandry practices.

Butyrate in combination with forskolin alleviates necrotic enteritis,increases feed efficiency,and improves carcass composition of broilers

Background:The emergence of antimicrobial resistance has necessitated the development of effective alternatives to antibiotics for livestock and poultry production.This study investigated a possible synergy between butyrate and forskolin(a natural labdane diterpene)in enhancing innate host defense,barrier function,disease resistance,growth performance,and meat quality of broilers.Methods:The expressions of representative genes involved in host defense(AvBD9 and AvBD10),barrier function(MUC2,CLDN1,and TJP1),and inflammation(IL-1β)were measured in chicken HD11 macrophages in response to butyrate and forskolin in the presence or absence of bacterial lipopolysaccharides(LPS).Intestinal lesions and the Clostridium perfringens titers were also assessed in C.perfringens-challenged chickens fed butyrate and forskolincontaining Coleus forskohlii(CF)extract individually or in combination.Furthermore,growth performance and carcass characteristics were evaluated in broilers supplemented with butyrate and the CF extract for 42 d.Results:Butyrate and forskolin synergistically induced the expressions of AvBD9,AvBD10,and MUC2 in chicken HD11 cells(P<0.05)and the synergy was maintained in the presence of LPS.Butyrate and forskolin also suppressed LPS-induced IL-1βgene expression in HD11 cells in a synergistic manner(P<0.05).The two compounds significantly reduced the intestinal lesions of C.perfringens-challenged chickens when combined(P<0.05),but not individually.Furthermore,butyrate in combination with forskolin-containing CF extract had no influence on weight gain,but significantly reduced feed intake(P<0.05)with a strong tendency to improve feed efficiency(P=0.07)in a 42-d feeding trial.Desirably,the butyrate/forskolin combination significantly decreased abdominal fat deposition(P=0.01)with no impact on the carcass yield,breast meat color,drip loss,or pH of d-42 broilers.Conclusions:Butyrate and forskolin has potential to be developed as novel antibiotic alternatives to improve disease resistance,feed efficiency,and carcass composition of broilers.

Discovery of natural products capable of inducing porcine host defense peptide gene expression using cell-based high throughput screening

Background:In-feed antibiotics are being phased out in livestock production worldwide.Alternatives to antibiotics are urgently needed to maintain animal health and production performance.Host defense peptides(HDPs)are known for their broad-spectrum antimicrobial and immunomodulatory capabilities.Enhancing the synthesis of endogenous HDPs represents a promising antibiotic alternative strategy to disease control and prevention.Methods:To identify natural products with an ability to stimulate the synthesis of endogenous HDPs,we performed a high-throughput screening of 1261 natural products using a newly-established stable luciferase reporter cell line known as IPEC-J2/pBD3-luc.The ability of the hit compounds to induce HDP genes in porcine IPEC-J2 intestinal epithelial cells,3D4/31 macrophages,and jejunal explants were verified using RT-qPCR.Augmentation of the antibacterial activity of porcine 3D4/31 macrophages against a Gram-negative bacterium(enterotoxigenic E.coli)and a Gram-positive bacterium(Staphylococcus aureus)were further confirmed with four selected HDP-inducing compounds.Results:A total of 48 natural products with a minimum Z-score of 2.0 were identified after high-throughput screening,with 21 compounds giving at least 2-fold increase in luciferase activity in a follow-up dose-response experiment.Xanthohumol and deoxyshikonin were further found to be the most potent in inducing pBD3 mRNA expression,showing a minimum 10-fold increase in IPEC-J2,3D4/31 cells,and jejunal explants.Other compounds such as isorhapontigenin and calycosin also enhanced pBD3 mRNA expression by at least 10-fold in both IPEC-J2 cells and jejunal explants,but not 3D4/31 cells.In addition to pBD3,other porcine HDP genes such as pBD2,PG1-5,and pEP2C were induced to different magnitudes by xanthohumol,deoxyshikonin,isorhapontigenin,and calycosin,although clear gene-and cell type-specific patterns of regulation were observed.Desirably,these four compounds had a minimum effect on the expression of several representative inflammatory cytokine genes.Furthermore,when used at HDP-inducing concentrations,these compounds showed no obvious direct antibacterial activity,but significantly augmented the antibacterial activity of 3D4/31 macrophages(P<0.05)against both Gram-negative and Gram-positive bacteria.Conclusions:Our results indicate that these newly-identified natural HDP-inducing compounds have the potential to be developed as novel alternatives to antibiotics for prophylactic and therapeutic treatment of infectious diseases in livestock production.

Development and evaluation of a herbal formulation with antipathogenic activities and probiotics stimulatory effects

Searching alternative feed antibiotics is always a study hotspot in the field of animal production. In this study, the antipathogenic activities and probiotics stimulatory effects of 30 kinds of herbs were screened through Oxford cup method and Hungate roll method. 15 herbs showed significantly antibacterial activities（P〈0.05） against Escherichia coli, Salmonella enteritidis, Salmonella typhimurium and Staphylococcus aureus. Seven herbs showed greatly stimulatory promoting effects on Lactobacillus acidophilus and Bifidobacterium longum. Finally, five herbs were combined for the developed formulation with selective antibacterial properties and they were Mume Fructus（35%）, Isatidis Folium（25%）, Moslae Herba（20%）, Chrysanthemi Indici Flos（13%） and Bupleuri Radix（7%）. The herbal formulation showed significantly antibacterial abilities against four pathogens and stimulatory promoting abilities on two probiotics in vitro and the equivalent activities in broiler chickens in vivo against E. coli and L. acidophilus. The toxicity study showed it had no toxicity, which indicated that it would be a kind of preferred candidate for an alternative antibiotic in future animal production.

Porcine intestinal antimicrobial peptide as an in-feed antibiotic alternative improves intestinal digestion and immunity by shaping the gut microbiota in weaned piglets

Antibiotic resistance of pathogens,which is caused by the abuse of in-feed antibiotics,threatens the sustainable development of livestock production.The present study aimed to investigate the efficiency of porcine intestinal antimicrobial peptide(PIAP)as an alternative to in-feed antibiotics in terms of growth performance,intestinal morphology,digestive enzymes and immunity,and microbiota community of the post-weaning piglets.A total of 204 piglets(Duroc×Landrace×Yorkshire,weaned at 28 d age)with a similar body weight of 7.97±1.04 kg were randomly allocated to 4 groups(51 piglets per group):(1)control group:basal diet;(2)AB group:antibiotic,basal diet+chlortetracycline(1000 mg/kg from d 1 to24;500 mg/kg from d 25 to 37);(3)P1 group:basal diet+a relatively low dose of PIAP(400 mg/kg from d 1 to 24;300 mg/kg from d 25 to 37);(4)P2 group,basal diet+a relatively high dose of PIAP(600 mg/kg from d 1 to 24;500 mg/kg from d 25 to 37).The results showed that serum indicators of hepatocyte damage and relative organ weight were not affected by these treatments(P>0.05).Compared with the AB treatment,the P1 treatment remarkably decreased jejunal crypt depth and increased jejunal and ileal villus height:crypt depth ratio(P<0.05).The values of jejunal maltase,lactase,sucrase,intestinal alkaline phosphatase,and secretory immunoglobulin A(SIg A)in the P1 group were sharply increased compared with those in the control and P2 groups(P<0.05).Compared with the control group,the P1 group decreased serum concentrations of D-lactate,diamine oxidase,and endotoxin(P<0.05),and increased the abundance of Lactobacillus reuteri(P<0.05)in the colonic feces.Furthermore,there was a positive correlation between the abundance of L.reuteri and the concentrations of maltase,lactase,sucrase,and SIg A(P<0.05).Collectively,dietary supplementation with a relatively low dose of PIAP(400 mg/kg from d 1 to 24;300 mg/kg from d 25 to 37)demonstrates beneficial effects on intestinal morphology,digestive enzymes,immunity,and permeability by shaping the gut microbiota composition in weaned piglets.This study will provide a valuable reference for using PIAP as an in-feed antibiotic alternative in swine production.

Dietary modulation of endogenous host defense peptide synthesis as an alternative approach to in-feed antibiotics

Traditionally, antibiotics are included in animal feed at subtherapeutic levels for growth promotion and disease prevention.However, recent links between in-feed antibiotics and a rise in antibiotic-resistant pathogens have led to a ban of all antibiotics in livestock production by the European Union in January 2006 and a removal of medically important antibiotics in animal feeds in the United States in January 2017.An urgent need arises for antibiotic alternatives capable of maintaining animal health and productivity without triggering antimicrobial resistance.Host defense peptides(HDP) are a critical component of the animal innate immune system with direct antimicrobial and immunomodulatory activities.While in-feed supplementation of recombinant or synthetic HDP appears to be effective in maintaining animal performance and alleviating clinical symptoms in the context of disease, dietary modulation of the synthesis of endogenous host defense peptides has emerged as a cost-effective,antibiotic-alternative approach to disease control and prevention.Several different classes of smallmolecule compounds have been found capable of promoting HDP synthesis.Among the most efficacious compounds are butyrate and vitamin D.Moreover, butyrate and vitamin D synergize with each other in enhancing HDP synthesis.This review will focus on the regulation of HDP synthesis by butyrate and vitamin D in humans, chickens, pigs, and cattle and argue for potential application of HDP-inducing compounds in antibiotic-free livestock production.

Implications of butyrate and its derivatives for gut health and animal production

Butyrate is produced by microbial fermentation in the large intestine of humans and animals.It serves as not only a primary nutrient that provides energy to colonocytes, but also a cellular mediator regulating multiple functions of gut cells and beyond, including gene expression, cell differentiation, gut tissue development, immune modulation, oxidative stress reduction, and diarrhea control.Although there are a large number of studies in human medicine using butyrate to treat intestinal disease, the importance of butyrate in maintaining gut health has also attracted significant research attention to its application for animal production, particularly as an alternative to in-feed antibiotics.Due to the difficulties of using butyrate in practice(i.e., offensive odor and absorption in the upper gut), different forms of butyrate,such as sodium butyrate and butyrate glycerides, have been developed and examined for their effects on gut health and growth performance across different species.Butyrate and its derivatives generally demonstrate positive effects on animal production, including enhancement of gut development, control of enteric pathogens, reduction of inflammation, improvement of growth performance(including carcass composition), and modulation of gut microbiota.These benefits are more evident in young animals, and variations in the results have been reported.The present article has critically reviewed recent findings in animal research on butyrate and its derivatives in regard to their effects and mechanisms behind and discussed the implications of these findings for improving animal gut health and production.In addition, significant findings of medical research in humans that are relevant to animal production have been cited.

Potential of blended organic acids to improve performance and health of broilers infected with necrotic enteritis

Organic acids(OA)and their blends have been shown to positively affect performance and health of broilers.However,the data in the literature are not consistent.This study examined the potential of blended short-chain fatty acids(SCFA)with medium-chain fatty acids(MCFA)as alternatives to antibiotic growth promoters(AGP)on performance,health and welfare of broilers infected with necrotic enteritis(NE).The additives used were:A)a blend of SCFA,MCFA,and a phenolic compound(SMP);B)a blend of free and buffered SCFA with MCFA(SMF);C)a blend of free and buffered SCFA with a high concentration of MCFA(SHM).A total of 1,404 Ross 308 one-day-old male parental chicks were randomly distributed into 78-floor pens with 13 replicates of 18 birds each.Six treatments were the following:T1,unchal-lenged control(UCC);T2,challenged control(CHC);T3,challenged group plus zinc bacitracin(BAC);T4,challenged group plus additive SMP;T5,challenged group plus additive SMF;T6,challenged group plus additive SHM.Challenged birds were gavaged with Eimeria spp.on d 9 and Clostridium perfringens EHE-NE18 on d 14.Post NE challenge and cumulatively,BWG,FCR,and nutrient digestibility of birds were compromised(P<0.05)by NE challenge indicating a successful induction of sub-clinical NE.Additive SHM had higher BWG compared to CHC and BAC groups(P=0.001;d 10 to 24)but not different from SMP and SMF groups(P>0.05).All the 3 additive groups had lower FCR compared to CHC(P=0.001;d 0 to 35),and exhibited similar jejunal lesions(d 16)compared to BAC and apparent ileal protein di-gestibility(d 21)compared to UCC and BAC groups(P>0.05).Birds in additive SHM group had a higher concentration of serum IgA compared to all groups(P=0.001)except additive SMF(P>0.05;d 21).All the additive groups had lower footpad dermatitis and hock burns compared to CHC(P<0.05).The findings suggest the potential of blended OA as alternatives to BAC to protect broilers from NE indicated by improved FCR,immunity,digestibility,and bird welfare.

Organic acid blends improve intestinal integrity,modulate short-chain fatty acids profiles and alter microbiota of broilers under necrotic enteritis challenge

Controlling enteric diseases of broilers is crucial.Among many additives,organic acids(OA)and their blends are gaining attention to combat diseases in the post-antibiotic era.The current study evaluated the potentials of short-chain fatty acids(SCFA)and medium-chain fatty acids(MCFA)blends and/or phenolic compounds on intestinal integrity,intestinal pH,caecal microbiota,and caecal SCFA profiles of broilers under necrotic enteritis(NE)challenge.The additives used were:(A)a blend of SCFA,MCFA,and a phenolic compound(SMP),(B)a blend of free and buffered SCFA with MCFA(SMF),and(C)a blend of free and buffered SCFA with a high concentration of MCFA(SHM).A total of 1,404 male parental chicks of Ross 308 broilers were randomly allocated to 78 floor pens on hatching day with 6 treatments replicated 13 times with 18 birds per pen.The treatments were:UCC,unchallenged control;CHC,challenged control;BAC,challenged group plus zinc bacitracin;SMP,challenged group plus additive SMP;SMF,challenged group plus additive SMF;SHM,challenged group plus additive SHM.Birds were challenged with field-strain Eimeria spp.on d 9 and Clostridium perfringens on d 14.Birds challenged with NE increased fluorescein isothiocyanate dextran(FITC-d)concentration in serum,reduced acetate and butyrate concentrations,and increased Bacteroides and C.perfringens load in the caeca(P<0.05).Birds fed additives decreased FITC-d from gut to serum,reduced Bacteroides(d 16,P<0.05)and numerically reduced C.perfringens load compared to CHC group.Birds fed additive SHM had higher concentrations of acetate and butyrate(d 21,P<0.05)than CHC group but were not different from SMP and SMF groups.All the additives exhibited similar intestinal protection against NE compared to the BAC group indicated by FITC-d concentration in serum,acetate,propionate and butyrate concentrations in the caeca,and caecal bacterial loads except for the C.perfringens(P>0.05).The SMP group had a higher load compared to BAC(P<0.05).These findings suggest the promising effects of OA blends as alternatives to BAC to ameliorate the impact of NE challenge of broilers as indicated by improved intestinal health.