鸡坏死性肠炎生物性防控研究进展

鸡坏死性肠炎(necrotic enteritis,NE)是现代化肉鸡集约养殖生产中最为突出的肠道疾病之一,给家禽产业带来了巨大的经济损失。随着世界范围内的立法限制、禁用抗生素生长促进剂,鸡坏死性肠炎的发病率在全球范围内呈上升趋势,这对家禽的生产和健康产生严重威胁。因此,迫切需要新的技术和新的产品代替抗生素来预防和控制鸡坏死性肠炎。作者着眼于NE的危害和疫苗、噬菌体、卵黄抗体、植物提取物、酸化剂、益生菌、低聚糖与微生物多糖等生物性防控进展,综述了目前有效预防和控制鸡坏死性肠炎的生物性措施的最新研究情况,既为鸡坏死性肠炎生物性防控提供技术参考,也为其深入研究提供了理论思考。     

Necrotic enteritis-producing strains of Clostridium perfringens displace non-necrotic enteritis strains from the gut of chicks

We inoculated broiler chicks with mixtures of Clostridium perfringens strains to investigate the single strain dominance observed in natural cases of necrotic enteritis (NE) [Nauerby, B., Pedersen, K., Madsen, M., 2003. Analysis by pulsed-field gel electrophoresis of the genetic diversity among Clostridium perfringens isolates from chickens. Vet. Microbiol. 94, 257-266]. Pre-inoculation bacteriologic culture of chick intestines yielded up to six pulsed-field gel electrophoresis (PFGE) types of C. perfringens. Birds developed typical NE lesions in response to administration (2x per day for 4 days) of a combined inoculum comprising one NE strain (JGS4143, PFGE pattern 8) and four non-NE strains (from piglet necrotizing enteritis, chicken normal flora, human gas gangrene, and bovine neonatal enteritis). After inoculation commenced, only the NE strain was recovered through the first post-inoculation day, in spite of intense efforts to recover pre-challenge flora strains and the other challenge strains. Thereafter, pre-inoculation and previously undetected PFGE types were found, and JGS4143 became undetectable. Birds inoculated simultaneously with five NE strains (from disease in chickens or turkeys, and including JGS4143) also developed lesions, but again only JGS4143 was recovered through the 1st day post-challenge. At that time, birds began to be repopulated with pre-challenge PFGE types. Two NE strains (JGS4143 and JGS4064) produced bacteriocins, which inhibited each other and normal flora strains (n=17), while normal flora strains inhibited neither NE strains nor each other. Thus, it appears that naturally occurring dominance of the gut by NE strains can be reproduced experimentally. Bacteriocins directed against normal flora could possibly provide the necessary advantage, although inhibition of one NE strain by another suggests that other factors may be partially or completely responsible for the dominance.     

Dietary supplementation of essential oils and lysozyme reduces mortality and improves intestinal integrity of broiler chickens with necrotic enteritis

The objective of this study was to investigate the individual and combined effects of essential oils (EO; comprised of thymol and carvacrol) and lysozyme on experimental NE in broiler chickens. A total of 320 1-day-old chicks were randomly assigned to five treatment groups: no-challenge control (NC), NC + C. perfringens challenge (CC), CC + 120 mg/kg of EO, CC + 100 mg/kg of lysozyme, and CC + 120 mg/kg of EO + 100 mg/kg of lysozyme. The results showed that EO or lysozyme decreased the mortality, alleviated the gut lesions, inhibited the liver Enterobacteriaceae carriage, and increased the villus height of the ileum compared with CC (p < .05), although the proliferation of C. perfringens in the ileum was not inhibited (p > .05). Moreover, EO or lysozyme was found to decrease the ileal concentration of sialic acid and the Mucin2 mRNA expression (p < .05). However, the blend of EO and lysozyme did not display significant effect on the NE-associated mortality or gut damage in contrast with CC (p > .05). In conclusion, these findings suggest the similar protective effects of EO and lysozyme in NE-associated mortality and intestinal impairment, but their blend did not exhibit ameliorative effect.     

鸡梭菌性肠炎研究概论

从病原学、流行病学、症状及病变、致病机理、诊断、治疗及预防、免疫进展等方面对鸡梭菌性肠炎进行介绍,并对该病未来研究热点进行了展望,为开展鸡梭菌性肠炎的基础研究、疾病预防控制提供参考。     

A framework for assessing the efficacy of antimicrobials in the control of necrotic enteritis in broiler chickens

This review presents a framework for assessing the efficacy of antimicrobials used to control necrotic enteritis (NE) caused byClostridium perfringens (CP) in the context of susceptibility testing and clinical efficacy, and their potential interactions with the intestinal microbiota of poultry. Practitioners have traditionally based their choice of antimicrobial agent on antimicrobial susceptibility testing, but there appears to be a lack of correlation with clinical efficacy for in-feed antimicrobials (particularly bacitracin and virginiamycin). Resistance patterns of CP and antimicrobials have been monitored using epidemiological cutoffs for minimal inhibitory concentration (MIC), which are not intended to guide therapy. Also, most data have been determined using CP isolates from healthy birds (i.e., potentially from commensal strains not known to be clinically relevant). It is believed that NE is caused by specific virulent CP strains (and potentially other bacteria) that proliferate and displace these commensals. The presence of resistant commensals is not necessarily detrimental (and may even be beneficial) if they inhibit the single CP strain dominance effect observed in acute NE. The choice of antimicrobial therapy in a clinical setting should thus be based on a variety of factors, including an accurate diagnosis, results of efficacy studies, prior experience at the premises in question, and interpretation of MIC data, recognizing that it is not necessarily well correlated with clinical efficacy.     

Research Progress on Prevention and Treatment of Necrotic Enteritis in Livestock

Necrotic enteritis is an acute gastrointestinal infectious disease with high morbidity and mortality which caused by Clostridium perfringens. The disease not only harms the livestock health and animal welfare,but also has been an emerging threat for breeding industry and human health. Antibacterial drugs played a positive role on preventing this disease,however,drug-resistant strains were increasing with irrational use of antibiotics,the incidence of necrotic enteritis has drastically increased, prevention and treatment of it faced severe challenges. The author reviewed the characteristics of necrotic enteritis include the etiology,physicochemical properties, epidemiology and clinical signs,at the same time, the control measures and common drugs were summarized,and the new development trend and direction for prevention and treatment necrotic enteritis was objective analyzed, aiming to establish a comprehensive understanding of the disease,provide references for prevention and treatment of the disease.     

畜禽坏死性肠炎防制研究进展

畜禽坏死性肠炎主要是由产气荚膜梭菌引起的一种急性消化道传染病,具有较高的发病率和死亡率。该病不仅损害畜禽健康,影响动物福利,而且对养殖业发展及人类健康造成了严重威胁。抗菌药的出现对该病起到了积极限制的作用,然而随着抗菌药的不合理使用,耐药菌株不断增加,坏死性肠炎的发病率呈现升高的趋势,防制坏死性肠炎面临严峻挑战。作者从坏死性肠炎的特征入手,综述了坏死性肠炎的病原学、理化特性、流行病学、临床症状等,与此同时对坏死性肠炎的防制措施及目前常用药物进行了总结,客观分析了防制坏死性肠炎的趋势与发展方向,旨在健全对该病的认识,为坏死性肠炎的防制研究提供参考。     

Use of Bacitracin and Roxarsone to Reduce Salmonella Heidelberg Shedding Following a Necrotic Enteritis Challenge Model

This study was performed to determine if the enteric disease necrotic enteritis results in higher shedding of Salmonella. Fifty percent of the chicks per pen were challenged with a naladixic acid-resistant Salmonella Heidelberg. A necrotic enteritis challenge model using a coccidia vaccine to induce intestinal epithelium damage was used to demonstrate that neither the disease necrotic enteritis nor the control of that disease with the antibiotic bacitracin methylene disalycilate had an effect on the incidence of Salmonella Heidelberg. However, the feed additive 3-nitro-4-hydroxyphenylarsonic acid, which controls the cecal coccidia Eimeria tenella, significantly reduced the amount of Salmonella Heidelberg in the environment of the chick as measured by dragswabs and also reduced the number of ceca positive in the contact chicks.     

Potential of a mixture of eugenol and garlic tincture to improve performance and intestinal health in broilers under necrotic enteritis challenge

Plant extracts(PE)are gaining increased attention as potential alternatives to in-feed antimicrobials(AM)due to their known antimicrobial activities.This study was conducted to examine the potential of PE,a microencapsulated product composed of eugenol and garlic tincture as an alternative to AM-agent on performance and intestinal health in broilers under necrotic enteritis(NE)challenge.A total of 960 dayold mixed-sex Cobb 500 chicks were randomly distributed to 48-floor pens with 6 treatments replicated 8 times with 20 birds each.The 6 treatments were as follows:UC,unchallenged control;CC,challenged control;PE,challenged group plus PE;AM,challenged group plus AM;FAP,challenged group plus a full dose of AM with PE;HAP,challenged group plus a half dose of AM with PE in starter,grower and finisher phases.Birds in the challenged groups were inoculated with Eimeria spp.on d 9 and Clostridium perfringens on d 14.The body weight gain(BWG),feed intake(FI),feed conversion ratio(FCR),and livability of birds were compromised,and intestinal lesions and mortality were increased(P<0.05)by NE challenge,illustrating a successful clinical NE challenge.Birds fed AM had higher BWG and FI,and lower FCR,mortality,and intestinal lesions compared to the CC group(P<0.05).Birds fed PE had improved FCR(P<0.05)and livability(5.8%)in an overall period compared to the CC group.On d 16,PE supplementation reduced ileal lesion scores in only male birds(P<0.05).Birds fed PE had decreased Eimeria maxima and Eimeria acervulina oocyst counts in caecal content(P<0.05).Birds fed PE had decreased Eimeria brunetti and total oocyst counts in caecal content,and E.acervulina oocyst counts in ileal content in only female birds(P<0.05).On d 35,PE supplementation reduced variation of BW in both male and female birds and increased yellowness(b*value,14.4%)in the thigh.These findings suggest the potential of PE supplementation in diets to improve the performance and intestinal health of birds under clinical NE as indicated by improved FCR,livability,uniformity,reduced ileal lesions,oocyst counts and increased skin yellowness.However,the protective effect of PE may not be apparent in the presence of AM in the feed.     

鸡坏死性肠炎模型构建和发病机理研究进展

当前由于抗生素生长促进剂的限制和禁用,世界范围内鸡坏死性肠炎(Necrotic enteritis,NE)的发生率大幅上升,威胁着家禽产业及公众健康。了解NE的模型构建和发病机理对鸡NE的有效防控起着积极作用。文章综述了产气荚膜梭菌及其毒素、NE感染的组织生物学变化、NE诱导因素及试验模型建立方法和评价等的最新研究进展。     

Effect of Spray-Dried Plasma Form and Duration of Feeding on Broiler Performance During Natural Necrotic Enteritis Exposure

The effect of duration of feeding (continuous or discontinued after d 14) and form (granular vs. powder) of spray-dried plasma (SDP) on performance and mortality of broilers using used litter was evaluated with 240 Ross × Ross 308 male broilers (6 broilers per pen, 8 pens per treatment). Dietary treatments were control (no SDP) or SDP as powder or granular included in the pellet and fed continuously (d 0 to 35) or discontinued after d 14. During the experiment, broilers developed necrotic enteritis, and tissue cultures were positive for Escherichia coli and Salmonella, resulting in 50% mortality on control broilers. Addition of SDP to the feed improved (P < 0.05) average daily gain, feed intake, and feed efficiency for each period of the study (d 0 to 14, 15 to 28, 29 to 35, and 0 to 35). Continuous feeding of SDP improved (P < 0.05) average daily gain, feed intake, and feed efficiency from d 15 to 35 compared with broilers fed SDP to d 14. Liveability was improved (P < 0.05) in broilers consuming SDP either for 14 d or continuously throughout the experiment compared with control broilers. Spray-dried granular plasma was more effective than spray-dried powder plasma from d 0 to 14. The results of this experiment confirmed that SDP improved broiler growth rate, feed intake, feed efficiency, and minimized enteric challenge associated with necrotic enteritis with maximal protection afforded by continuous feeding. The response to SDP was independent of age of the broiler.     

Emerging Technologies in Microbial Ecology Aid in Understanding the Effect of Monensin in the Diets of Broilers in Regard to the Complex Disease Necrotic Enteritis

Necrotic enteritis is a complex disease condition of broiler chickens, commercial layer pullets, and turkeys and requires the presence of a toxigenic strain of Clostridium perfringens, alteration of bird diets, and damage to the intestinal epithelium. All of these alone, but especially in combination, result in significant alterations of the intestinal microflora. The intestinal microflora is part of a complex ecosystem that is involved in augmenting intestinal development, immune surveillance, and competitive exclusion against pathogenic organisms. However, when the microflora fails to protect the mucosa from pathogens, antimicrobials are used to reduce the numbers of pathogenic organisms or to prevent their colonization of the intestine. We were interested in studying the effects of monensin on the bacterial community within the ileum of chickens because ionophore antimicrobials are commonly used to prevent Eimeria infections in broilers. We used two 16S ribosomal DNA community analysis protocols, terminal restriction fragment length polymorphism analysis combined with 16S rDNA clone libraries. These methods showed that monensin caused significant alterations in the microbial community structure of the ileum. Whereas the ileal bacterial community of control birds primarily consisted of lactobacilli, monensin-treated birds had communities rich in clostridia. None of the birds exhibited signs of intestinal disease or mucosal lesions, which suggested that the clostridia were avirulent. Although the therapeutic benefits of monensin may largely result from its anticoccidial effects, its ability to foster a competitively exclusive bacterial community may contribute to the intestinal health of birds, thus preventing the development of necrotic enteritis.     

Dietary inclusion of arabinoxylo-oligosaccharides in response to broilers challenged with subclinical necrotic enteritis

1. This study investigated the prebiotic properties of arabinoxylo-oligosaccharides (AXOS) produced both in situ and in vitro for their activity against the onset of necrotic enteritis in broiler chickens.

2. A 2 × 3 factorial arrangement was applied, including necrotic enteritis challenge (challenged/unchallenged) and three dietary treatments from d 10 to 21. A wheat–soy commercial-type basal-grower diet was fed with 2% of the wheat proportion replaced by the same amount of either arabinoxylan (AX), AXOS produced from hydrolysing AX with 16 000 BXU (birch xylanase unit) xylanase in vitro or AX fed with 16 000 BXU xylanase (AX + E). Necrotic enteritis (NE) challenge was induced by orally infecting birds with a vaccine strain of Eimeria oocysts at d 9 of age followed by oral gavage of a freshly prepared Clostridium perfringens broth at d 14.

3. The challenge depressed growth performance, induced gross lesions and reduced ileal viscosity at d 10–21. Birds fed on the AXOS diet had numerically less severe gross lesions, improved feed conversion at d 0–16 and lower ileal viscosity at d 16 compared to birds fed on AX. Weight gain of the unchallenged birds ranked as follows in terms of the diets: AXOS > AX + E > AX. AX + E produced a lower ileal viscosity compared to the AX treatment but only led to marginal improvements in performance and intestinal lesion scores.

4. Caecal short-chain fatty acid (SCFA) concentration was higher in birds fed on AXOS and AX + E compared to those fed on AX and was higher in the challenged birds compared to the unchallenged birds. Gizzard pH was lower in birds fed on AX + E compared to those fed on AXOS at d 16. Challenged birds had lower ileum pH compared to the unchallenged birds at d 16 and 21.

5. Results of this study suggest that AXOS appeared to be efficacious prebiotics, as highlighted by improvements in feed conversion ratio and increased SCFA production. Future studies are warranted to elucidate the types of AXOS that are most active against NE and the mechanisms by which different levels of AXOS enhance bird performance.