Optimizing Intestinal Health in birds raised without antibiotics

A 2012 survey of the US broiler industry to determine and rank production challenges indicated that gut health management was paramount in the minds of those involved with live production (23). This is not surprising since intestinal integrity determines feed efficiency, the most important economic driver of the meat industry. Since then, some significant changes in the industry have sharpened the focus on managing intestinal health.

The Poultry industry is experiencing a particularly profitable period. Over the last twelve months, a nationwide shortage of pork, beef and chicken has induced a significant strengthening in the price of meat and this has coincided with a fall in the price of corn, the primary ingredient in US animal diets (35). While this would normally ease focus on the intensity of intestinal health management, this has not been the case because the status quo of traditional bacterial and protozoal enteropathy control strategies have been concomitantly been shattered by three occurrences. Firstly, the inference that the prevalence of gangrenous dermatitis is associated with the use of ionophores (46), secondly, the voluntary removal of 3-nitro from broiler feed in 2012 and thirdly, a recent statement of intent by a leading fast food chain to only sell chicken meat raised without in-feed antimicrobials within the next five years (5).

 

Although poultry meat production systems are all-in-all-out in nature, they are, from a gut flora perspective, a continuous system. Members of the gut microbial community surviving in the house environment are carried over from one cycle to the next and thus serve as the “seed stock” for the gut flora of the next placement (33). While in-feed antibiotics can alter the gut flora within a couple of weeks, it takes several grow-out cycles to change the house (litter) flora (3, 29, 33, 48, 49). This is by no means a new concept, both rotation and shuttle programs have been used for decades to avoid the lack of response to in-feed antibiotics following their persistent use.

The realization that even minor changes in intestinal microbial community composition can affect long term productivity through incremental displacement and replacement of the house flora has highlighted the significance of microbial community management (40). Attention to detail is more critical than ever. The efficiency of nutrient assimilation hinges on the early establishment and maintenance of a favorable gut lumen environment. In a drug free production system the emphasis shifts from fighting the unfavorable organisms with antibiotics to nurturing the favorable organisms; working with nature to ensure a favorable and stable intestinal ecology. In its simplest format this involves: seeding the gut with favorable intestinal microbiota, feeding these organisms to ensure that they rapidly dominate the intestinal microbiota and weeding out the unfavorable organisms.

 

The first organisms to colonize the gut direct the evolution and composition of the climax flora by creating the microenvironment necessary for complex microbial community development (27). Colonization of the gut with pioneer bacteria species, that are able to modulate expression of genes in the gut epithelia to optimize nutrient assimilation and create favorable conditions for establishment of a stable and beneficial climax flora, should be the starting point of any gut health management program (21, 27). In addition, competitive exclusion has long been recognized as a means of preventing pathogen colonization of the intestinal tract and probiotics have recently been shown to suppress colonization of the intestine with Brachyspira pilosicoli (34), Clostridium perfringens (42), Campylobacter jejuni (45), and Salmonella enteritidis (55). Since the first organisms to gain access to the hatchling gut originate from the parent, steps to control gut health should start at the parent flock level. Vertical transmission of gut inhabitants (from parent to offspring) can be transovarial (inside the egg) or as a result of contamination during oviposition (28, 30, 41)

In the artificially clean hatchery environment, even low doses of beneficial bacteria can significantly improve resistance to pathogen colonization, and artificial seeding of the gut at an early age has been shown to be beneficial (6, 15-17, 19, 24-26, 32, 36, 38).

 

In addition to seeding the gut with the correct pioneer species, it is crucial to enhance their ability to proliferate, compete and colonize, so as to avoid pathogen proliferation. Weak organic acids can be used to change gut flora community structure (39, 43). As weak proton donors, they are able to escape inactivation in the upper intestinal tract (proventriculus and gizzard), while their presence in the small intestine modifies microbial community composition (44). Endogenous short chain fatty acids have a microbiota stabilizing effect and butyrate in particular has been shown to stimulate the production of host defence peptides (β-Defensins and Cathelicidins) (54). By providing a competitive advantage to the acid tolerant organisms such as the Lactobacilli and a competitive disadvantage to the acid intolerant organisms like the Clostridia, it is possible to guide the development microbiota composition (13, 44). Such manipulation of the microbiota has both short and long term implications.

Unfavorable organisms are in general much more competitive in the environment of the lower intestinal tract and their replication is normally kept in check by intense competition for a limited source of nutrients (58). Any factor that reduces digestion efficiency in the upper gastrointestinal tract, or increases nitrogen turnover in chickens, could potentially alter cecal ecology. Urine (uric acid) and feed (undigested protein) nitrogen are used by cecal flora to synthesize microbial protein (4), a process that unfortunately yields toxic metabolites and causes dysbacteriosis (12, 14, 22). In contrast, volatile fatty acids (VFA) formed during carbohydrate degradation, have antibacterial activity which has a stabilizing effect on the cecal ecology (2, 7, 8, 13, 53, 56, 57). Since cecal ecology is adversely affected by protein maldigestion, exogenous enzymes designed for protein ingredients can be used to help stabilize cecal flora communities. The amount of protein nitrogen reaching the ceca can be further reduced if nutrient credit allocation permits a reduction in dietary protein (47).

 

The traditional approach to weeding out unfavorable organisms has been through the addition of a low level of antibiotic to the diet. The consumer has, rightly or wrongly, made the link between the emergence of antibiotic resistant strains of human pathogens and antibiotic use in animal agriculture. This approach to intestinal microbiota management is rapidly falling from grace. While antimicrobial substitutes such as essential oils and in-feed bacillus probiotics have become popular, the long term sustainability/future of these products may come into question; they are after all antibiotics by a different name. Alternatives that utilize a different mechanism of action which avoids the negative aspects of low dose antimicrobial use is, from most perspectives, a more suitable solution.

As colonization proceeds, organisms attach to one another and the epithelium by a series of fibrils, to form a tightly adherent mat over the gut surface (20). Pathogens are thereby precluded access to the epithelial surface and their ability to colonize is compromised by a process of competitive exclusion (37). Microbe attachment to host cell docking sites on the intestinal epithelium is dependent on surface molecule structure and is the pivotal first step in the colonisation and infection of the gut (20, 31, 50, 52) . Since several gut pathogens recognise and attach to specific gut epithelia glycoproteins, products that mimic these docking sites are also useful in preventing attachment and reducing the risk of pathogen colonization (1, 18, 20, 51).

Pathogen induced inflammation of the gut lining stimulates mucus secretion, increased paracellular permeability, and accelerated feed passage (peristalsis) (10, 11). The cascade of events that follows is self-perpetuating. Increased permeability enhances toxin and agent penetration, which in turn stimulates inflammation, and the resulting increase in mucus production attracts mucolytic species such as Clostridium perfringens, which produce tissue damaging cytotoxins (9, 10); a vicious cycle ensues.

 

Strategies to improve gut health in commercial operations need to be cost effective, sustainable, farm specific and holistic. Intervention / product selection needs to be science based but practical and each intervention must address the specific objective for its inclusion. Efforts to nurture and stabilize a favorable intestinal microbiota with alternative approaches have shown promise in addressing the negative impact of in-feed antibiotic removal and use. While there are several opportunities and product options to achieve this, there are three simple interventions that have demonstrated particular promise. By seeding the hatchling gut with favorable organisms, feeding these organisms with an appropriate organic acid, and weeding out the unfavorable competitors with a type-1 fimbriae blocker, it is possible to improve performance by accelerating the evolution of, and maintain the stability of, a favorable intestinal microbiota.

 

 

 

 

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