Use of specifically formulated probiotics for early gastrointestinal tract development in neonatal chicks is a promising area that can have an effect on commercial poultry performance.
By ROSS E. WOLFENDEN and BILLY M. HARGIS*
*Dr. Ross Wolfenden is vice president of research and development at Pacific Vet Group-USA. Dr. Billy Hargis is a professor, director of the JKS Poultry Health Laboratory and the Tyson endowed chair for sustainable poultry health in the University of Arkansas-Fayetteville department of poultry science.
THE concept of beneficial enteric microflora is ages old, with fermented foods being used for their medicinal properties by the ancient Egyptians.
The practice of consuming fermented foods has continued to this day in virtually all regions of the world. This concept first achieved notoriety in western countries from the work of Nobel laureate Elie Metchnikoff in the early 1900s with the health and longevity of human populations within Bulgaria that consumed a particular variety of yogurt fermented with a lactic acid bacterium that he labeled Lactobacillus bulgaricus.
While intentional inoculation of ruminant animals with normal rumen contents has been practiced for centuries for various causes of ruminosis or ruminal dysbacteriosis, it was not until the work of Finnish researchers Nurmi and Rantala in the early 1970s (Nurmi and Rantala, 1973; Rantala and Nurmi, 1973) that the idea of early colonization by normal and beneficial bacteria gained traction for monogastric animals.
In these studies, using fecal transplants from normal adult chickens to neonatal chicks, the researchers demonstrated that chicks treated near-hatch with normal adult microflora were much more resistant to infection with salmonella. The magnitude of resistance of chicks to enteropathogens following exposure to mature normal mixed microflora was startling.
This led to a variety of segments within the worldwide poultry industry creating "autogenous" starter cultures from mature poultry sources that they hoped were healthy. The terminology used to describe this phenomenon was "competitive exclusion" (CE).
In several of these early experiments, it was found that starter cultures from different agricultural species did not perform as well as the host-derived cultures, foreshadowing the now understood host-adaptation for many (but not all) commensal enteric organisms. This was the seminal demonstration of lack of cross-species utility of undefined probiotic bacterial cultures.
Over time, this approach gained considerable traction among segments of the poultry industry in western countries. Because the microflora were from "donors," this meant that these types of non-defined cultures could contain non-beneficial organisms, beneficial organisms and incredible variability in the constitutive microflora within the would-be CE product. Inconsistent observations of modest to robust benefits of such cultures were widely observed, which allowed for the development of more-refined and somewhat safer commercial, but still undefined, CE products.
In 1998, the U.S. Food & Drug Administration approved the first "defined" CE product with a claimed 29 different species/biotypes of bacteria produced under continuous flow culture (Corrier et al., 1994b; Corrier et al., 1993; Hollister et al., 1999; Hume et al., 1996; Hume et al., 1998).
This technology was a step forward from the more traditional CE cultures in terms of consistency and documentation of positive effects but had major disadvantages due to poor stability — the product had to be stored at -70 degrees C and had a relatively short shelf life — and a high cost of production (Corrier et al., 1993; Hume et al., 1996).
Additionally, there was some suggestion that the effective dose was much lower than the labeled dosage. The ability to produce from identical seedstocks through the more expensive continuous flow fermentation convinced authorities that there was less risk of introduction of harmful bacteria, which was a definite risk factor of unknown magnitude with undefined cultures.
Undefined CE cultures were regulated out of the U.S. market — as well as the markets of most other developed countries — in the early 2000s, thus largely ending the era of undefined cultures.
Since that time, a number of generally recognized as safe lactic acid bacteria (LAB)-based and bacillus-based products have entered the market. Almost uniformly, these products are less expensive and more convenient to store, handle and administer than the early CE cultures.
While many of the products that have entered the market during the last 15 years have largely been untested with any scientific rigor, several products have been shown to have marked efficacy for improving growth, feed efficiency and even resistance to enteric infections with salmonellae and other pathogens (Flint and Garner, 2009; Higgins et al., 2005; Higgins et al., 2007; Higgins et al., 2011; Hong et al., 2005; Layton et al., 2013; Tellez et al., 2012; Torres-Rodriguez et al., 2007; Vicente et al., 2007).
Although the mechanisms of action of such products are not fully understood, many still consider the principles of CE first demonstrated by Nurmi and further defined by Mead and colleagues (Mead, 2000; Mead et al., 1996; Mead et al., 1989) as the primary mode of action. CE is thought to work by competition for nutrients and attachment sites and/or production of unfavorable metabolites targeted against pathogenic organisms.
Some strains have also been shown to produce carbohydrases, proteases, lipases and other enzymes that reduce viscosity of the ingesta and improve the ration's nutrient availability to the host (unpublished data from Pacific Vet Group-USA).
Interestingly, one well-characterized culture that has been widely used in poultry (FloraMax) was shown, through microarray analysis, to reduce inflammation of the intestine in as little as six hours post-administration in salmonella-challenged chicks, with simultaneous marked reductions in salmonella infections also observed (Higgins et al., 2011). This later observation may be of special interest in that it suggests that some effective LAB cultures actually have the ability to directly affect the chicken, presumably through innate toll-like receptors that line the intestinal tract.
This may be of particular interest in light of currently circulating (and published) hypotheses tha effective antibiotic growth promoters may actually work by direct anti-inflammatory action on the chicken rather than through true antimicrobial effects (Isolauri et al., 2002; Menard et al., 2004; Niewold, 2007).
While the current generation of probiotics is superior in terms of stability, cost and defined bacterial composition to past generations, these products still often suffer from expectations of performance that differ from their capabilities.
The message is that a single probiotic formulation works well across application methodologies (water applied, feed applied, daily administration, episodic administration), for multiple benefits (animal performance, control of foodborne pathogens, ammonia and disease, yogurt production, etc.) and in multiple species (poultry, swine, cattle and aquaculture).
Essentially, a one-size-fits-all approach has been taken, in many cases. However, while one probiotic isolate or combination of isolates may have multiple benefits, a single strain or culture is unlikely to work in all circumstances.
For example, strains of LAB used in dairy production have been selected for optimal growth at 50 degrees C or greater. With normal body temperatures of 37-40 degrees C for most poultry and livestock and water temperatures of 10-20 degrees C for most aquaculture applications, it is easy to see how a single bacterium or culture would not be optimal across all of these disparate applications since most bacteria grow best under relatively narrow temperature ranges.
Another example would be the suitability of probiotic bacteria for application in pelleted feeds. Most vegetative bacteria, such as LAB, are sensitive to temperatures in excess of 50 degrees C. since pellet mills generally operate at 80-85 degrees C (Cutlip et al., 2006; Furuta et al., 1980), vegetative cells will not survive steam pelleting in high numbers (Furuta et al., 1980).
As such, LAB is not well suited for application in diets prior to pelleting. The heat-resistant spore formed by some strains of bacillus can withstand temperatures of 100 degrees C for brief periods (Nicholson, 2002; Nicholson et al., 2000; Setlow, 2006), making them better suited for applications into pelleted feeds.
As probiotics have matured as a technology, forward-thinking researchers have shifted from developing probiotics as a catchall, one-size-fits-all treatment for all production problems in all species to more targeted applications to specific problems in specific species.
Recent research indicates that effective, scientifically formulated probiotics may have various positive effects in commercial poultry (Flint and Garner, 2009; Higgins et al., 2005; Higgins et al., 2007; Higgins et al., 2011; Hong et al., 2005; Layton et al., 2013; Tellez et al., 2012; Torres-Rodriguez et al., 2007; Vicente et al., 2007). These effects include maintenance of gut barrier function and reductions in lameness and necrotic enteritis, to name a few.
The probiotic field is just now beginning to deliver on its promise because it is now focused on identifying and developing tools to address specific problems in the poultry industry. One of the more exciting opportunities may actually be the pioneer colorization and stimulation of the neonatal gastrointestinal tract of commercial poultry.
During the last several years, the general interest in enteric microflora and their association with health, performance and disease has gained increasing attention in the poultry industry. This is particularly true in light of increasing feed costs and pressures associated with reduced usage of antibiotic growth promoters for several political and societal reasons.
One striking area of research has been on the effect of early colonization of the intestinal tract by beneficial versus harmful bacteria during the early neonatal development.
In humans, aseptic cesarean delivery of infants is associated with a variety of illnesses that may persist through life, including conditions such as allergies and asthma. It is now widely accepted and documented that human infants receive a healthy dose of beneficial microflora from their mothers during the birthing process as the child passes through the vaginal canal (Fooladi et al., 2013; Maynard et al., 2012).
Notably, these vaginally derived beneficial microflora are frequently LAB and are believed to be tremendously important for normal infant development, even though there is no evidence that these organisms persist in a more mature intestinal tract.
Along these lines, studies with animals that have been raised in sterile conditions and given sterile feed and air do not undergo normal intestinal development or function (Baba et al., 1991; Fukata et al., 1987). Regardless of animal species, from mice to chicks, animals raised under these conditions fail to develop normal villi, which are responsible for absorption of nutrients; they grow much more slowly and utilize feed approximately one-third less efficiently.
Indeed, the enteric-associated immune system is incredibly extensive, and immunologists have often referred to the gut as the largest immune organ in the body. Phenomenally, it's the interaction with early colonizers of beneficial microflora that is directly responsible for intestinal absorptive and immune capacity, and the effects of this colonization can last a lifetime (Rhee et al., 2004).
As previously mentioned, the bacterial species that are most beneficial and most effective for this early colonization, increased disease resistance and development of nutrient absorption capacity of the intestinal tract may not be the most effective colonizers of more mature intestinal systems. Similar to cesarean-delivered infants, commercial poultry do not get exposed to appropriate complex microflora either (Figure 1).
In commercial poultry, the timing and composition of microflora are essential for early performance during the first two weeks of life. Early performance has been clearly linked to final production efficiency and rate by researchers and poultry husbandry experts alike (Henderson et al., 2008; Wahlstrom, 2013).
The microbiological niches within the neonatal gastrointestinal tract are remarkably different from those of more mature intestinal tracts. Even in poultry raised under commercial or nearly commercial conditions, early seeding of the gut with a specifically formulated probiotic (FloraStart) resulted in improved seven-day weights, uniformity and increased early villus development (Figures 2-4).
While some very minor differences may be noted among neonatal humans, rodents and poultry, it is interesting that the effects on the permanent phenotype of each animal species can be altered by both the timing and composition of early intestinal bacterial colonization. Those probiotic bacteria that are most beneficial to growing animals may not be the most suitable for the unique space of the neonatal intestinal tract.
Given the importance of early performance to the final outcome of poultry flocks in terms of growth rate, feed efficiency, uniformity and mortality, it may be surprising that little attention has been given to selecting the most appropriate beneficial organisms for probiotic treatment of newly hatched chicks.
The use of probiotics is an ancient human practice, but the use of probiotics in poultry production is much more recent. During the last 40 years, the use of probiotics has progressed from the transplantation of feces from "healthy" adult hens into neonatal chicks as a way to decrease colonization by salmonella to a more mature technology focused on developing probiotic formulations to address specific, wide-ranging issues relevant to today's modern poultry industry.
While the specific modes of action by which these formulations work has not been fully defined, our understanding has increased exponentially from the early days. The development of probiotics specifically formulated for stimulation of early gastrointestinal tract development in neonatal chicks and/or poults is one promising area where scientifically formulated probiotics can have a substantial effect on the performance of commercial poultry.
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