2005 Poultry Science Association, Inc.
Alternatives to Antibiotics for Organic Poultry Production J. P. Griggs and J. P. Jacob1 Department of Animal Science, 1364 Eckles Ave., University of Minnesota, St. Paul, Minnesota 55108
Primary Audience: Producers, Nutritionists SUMMARY There is a variety of potentially useful ingredients that could be added to the feed or drinking water of a poultry flock to improve production or to reduce the spread of disease. Some of these potential ingredients have been tested in live poultry flocks; others have only been tested in a laboratory without the use of live birds. Most of the potential ingredients need to be more thoroughly tested in live birds and in real production flocks before they are be completely embraced by poultry producers. With current consumer preferences tending toward purchasing products from livestock grown without antibiotics, the ingredients presented in this paper should be studied more thoroughly for the beneficial applications they may have in poultry production. Key words: antibiotic, alternative, organic 2005 J. Appl. Poult. Res. 14:750–756
DESCRIPTION OF PROBLEM Organic livestock producers in the United States face unique challenges because of the limitations placed on them by the national regulations that define organic livestock production. These regulations prohibit the use of antibiotics for any reason [1]. It is important to note, however, that the regulations do require that animals raised in an organic system be treated with antibiotics if they become infected with a disease for which a nonantibiotic treatment is not available or has not been effective. Unfortunately, birds treated with antibiotics can no longer be marketed as organic. Because of this, there has been a big push to find alternative treatment methods for common poultry ailments. Much of this research has focused on reducing the prevalence of certain bacteria in experimentally challenged animals that are not necessarily 1
showing symptoms of a disease. Parameters studied include reductions in pathogenic bacteria; bird performance as measured by weight gain, egg production, feed conversion; and foodborne pathogens. Some of the products that have been tested to try to achieve these goals include probiotics, prebiotics, organic acids, and plant extracts.
PROBIOTICS A probiotic is a culture of a single bacteria strain, or mixture of different strains, that can be fed to an animal to improve some aspect of its health. Probiotics are also referred to as direct fed microbials (DFM). A variety of different types of bacteria, and in some cases even undefined cultures, have been tested as probiotics in poultry. The aim of many studies involving DFM has been to exclude the colonization of pathogens in the gastrointestinal tract of poultry.
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GRIGGS AND JACOB: ALTERNATIVES TO ANTIBIOTICS La Ragione et al. [2] showed that oral inoculation of Bacillus subtilis spores could reduce intestinal colonization of Escherichia coli O78:K80 in chickens. These results were observed only when the challenge occurred 24 h after the oral inoculation of B. subtilis. They did not observe any inhibition of E. coli O79:K80 when the challenge occurred 5 d after spore inoculation. The inability of B. subtilis spores to protect against the E. coli O79:K80 challenge when it occurred 5 d after the spores were introduced may be due to the observation that the number of spores present in the intestine gradually declined over time and may have only been present at high enough levels to be protective in the initial day or so following inoculation. In a study looking at the effects of B. subtilis on Salmonella Enteritidis and Clostridium perfringens in young chickens, La Ragione and Woodward [3] showed that B. subtilis spores reduced colonization of the pathogens when the spores were administered 24 h prior to challenge with each of the pathogens. Based on the protective effect observed when the challenge followed 24 h after the inoculation of the spores and the inability of the B. subtilis spores to maintain protection, La Ragione et al. [2] concluded the next step would be to test the efficacy of delivering the spores continuously in the drinking water of young chickens. Administration of the spores via drinking water would be a feasible method of delivery to use in commercial poultry production because the spores could be easily distributed across the entire flock and would be very likely to be ingested by all the birds in the flock on a daily basis. Other, nonspore-forming types of bacteria have also been examined as probiotics for poultry. One commonly studied genus is Lactobacillus. Jin et al. [4] screened 46 Lactobacillis isolates from chickens for their ability to attach to chicken ileal epithelial cells in vitro and found 12 that had at least a moderate ability to do so. Ehrmann et al. [5] demonstrated an in vitro method by which they could screen potential probiotic organisms and found 2 Lactobacillus strains that could colonize the ceca of ducks for 22 d. The findings reported in these studies [4, 5] are important because the ability to colonize the gastrointestinal tract is thought to be crucial for a probiotic to be successful.
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Salmonella and Campylobacter are the 2 most common bacterial causes of foodborne illness, and a few studies have shown that probiotics may be able to reduce the amount of these bacteria that are carried by chickens. Jin et al. [6] tested 12 Lactobacillus isolates described previously [5] for inhibition of 5 strains of Salmonella. This group found that all 12 Lactobacillus isolates inhibited the growth of the 5 strains of Salmonella. Morishita et al. [7] orally administered a mixture of L. acidophilus and Streptococcus faecium to chickens for the first 3 d of life. Six hours following the first treatment they orally challenged them with Campylobacter jejuni. They found that the chickens that received the treatment were colonized significantly less with C. jejuni than the chickens in the control group. In vitro growth inhibition of C. jejuni by bacteria isolated from chickens was demonstrated by Chaveerach et al. [8]. They discovered a Lactobacillus isolate with bactericidal activity against all the Campylobacter isolates they tested. Chang and Chen [9] reported in vitro inhibition of C. jejuni by a mixture of 4 Lactobacillus species. These results [7, 8, 9] show that feeding probiotics to poultry may change their gut microflora in a way that is beneficial to the health of consumers by reducing the number of potential foodborne pathogens carried by the birds. Some investigators have examined the effect of probiotics on production variables in poultry. Nahashon et al. [10] found that feeding layer diets supplemented with Lactobacillus resulted in greater feed consumption (g/hen), egg mass (g/hen per d), and egg weight (g/egg) than for hens receiving unsupplemented diets. Haddadin et al. [11] also tested the effect of feeding Lactobacillus to laying hens, specifically L. acidophiluss. They reported that hens receiving the bacteria had significantly better feed conversion (kg of feed: kg of eggs) and laid eggs that contained less cholesterol than the hens fed the control diet. These improvements were significant between levels of bacteria received; the birds receiving the most bacteria had the best feed conversion. The results of these 2 studies [10, 11] suggest that producers interested in increasing profits in their laying flocks may be able to do so by adding a Lactobacillus probiotic to the feed.
752 Many producers face problems associated with coccidiosis. Some recent work has shown that bacteria can inhibit Eimeria, the genus of protozoa responsible for coccidiosis [12]. The same researchers showed that Lactobacillus isolated from chickens produced factors that inhibited intestinal invasion by E. tenella. Invasion into the epithelium of the intestinal wall is necessary for the pathogenesis of this organism, so Lactobacillus bacteria may be able to reduce the severity of an infection. A study utilizing live chickens challenged with E. tenella would be a logical next step to test this hypothesis. Another group did perform a somewhat similar study utilizing live birds [13]. They reported that chickens given a Lactobacillis probiotic shed 75% fewer sporulated oocysts than the control group 6 to 9 d after challenge with E. acervulina. These 2 studies [12, 13] suggest that Lactobacillus may be a suitable alternative to conventional medications for treating an Eimeria infection in poultry. Studies utilizing an undefined mixture of bacteria as a probiotic have also been carried out. Soerjadi-Liem et al. [14] treated chicks at 3 d of age with a solution of native gut microflora and then challenged them with Campylobacter. This group found that only 4% of the chicks exposed to native gut microflora were infected at 56 d of age compared with 100% of the control group. Stavric et al. [15] used undefined cultures of fecal and cecal contents and cultures of 10, 25, and 50 defined organisms isolated from the undefined cultures to assess the ability of these mixtures to protect newly hatched chickens from a challenge of S. typhimurium. They reported that the best protection was achieved with both the undefined cultures and the mixture of 50 bacterial cultures. Their results suggest that a larger mixture of bacteria may be more protective than a probiotic containing only one specific organism. Cox et al. [16] used an undefined culture obtained from the cecal epithelial wall of adult turkeys as a competitive exclusion treatment of poults. They reported that after 6 wk, only 1 out of 30 cecal droppings from the treated group contained Salmonella compared with 14 of 30 from the control group, which suggested the undefined culture was protective against Salmonella. These 3 studies [14, 15, 16] suggest that it may be incorrect to assume there is a
JAPR: Review Article single probiotic organism that can be used to effectively protect poultry against all pathogens.
PREBIOTICS Prebiotics are nondigestible carbohydrates. Many of these carbohydrates are short chains of monosaccharides, called oligosaccharides. Some oligosaccharides are thought to enhance the growth of beneficial organisms in the gut, and others are thought to function as competitive attachment sites for pathogenic bacteria. Two of the most commonly studied prebiotic oligosaccharides are fructooligosaccharides (FOS) and mannanoligosaccharides (MOS). FOS can be found naturally in some cereal crops and onions [17]. MOS is obtained from the cell wall of yeast (Saccharomyces cerevisiae). Some studies of the application of FOS in poultry production have shown that these compounds may have potential benefits, but other studies have had inconsistent results. Waldroup et al. [18] were unable to show consistent effects on growth rate and feed efficiency in live broilers fed diets containing 0.375% FOS. In processed birds, they were unable to see any significant reduction in Salmonella contamination or dressing percentage. Fukata et al. [19] reported on 2 separate, but identical, experiments in which 0.1% FOS was added to feed for young chickens that were then challenged with Salmonella Enteritidis at 7 d of age. In only the second experiment did the chickens in the FOS treatment group show a significant reduction in Salmonella carriage in the ceca when compared with the control chickens at 1 and 7 d postchallenge. In neither experiment did FOS significantly reduce the amount of Salmonella Enteritidis found in the ceca 14 d postchallenge when compared with the control group. These researchers also attempted to quantify the changes in the bacterial microflora of the chicken ceca that result from feeding FOS [19]. They reported no significant differences between the control group and the FOS group in 7- or 21-d-old chickens. The failure of their FOS treatment to significantly effect the microbial population in the chicken ceca may be the reason for the inconsistent results they obtained in their first experiment. Other groups have studied various aspects of feeding FOS to chickens and have had more promising results. Bailey et al. [17] examined
GRIGGS AND JACOB: ALTERNATIVES TO ANTIBIOTICS the effect that feeding different levels FOS had on Salmonella colonization in experimentally inoculated chickens. They reported that diets with 0.375% FOS had little effect on colonization; however, when diets containing 0.75% FOS were fed to chickens, 12% fewer were colonized with Salmonella than in the control group. Xu et al. [20] studied the effect of FOS, at 4 levels of dietary inclusion, on growth performance and intestinal microflora in broilers. They reported that the diets containing 0.4% FOS resulted in significant improvements in average daily gain and feed efficiency compared with those fed the control diet. A lower inclusion level (0.2%) did improve feed efficiency significantly but not average daily gain. The 0.4% level was also associated with significantly more beneficial bacteria, Bifidobacterium and Lactobacillus, and significantly less E. coli in the cecum and small intestine. From the various studies that have investigated FOS [17, 18, 19, 20], it could be suggested that for FOS to be noticeably beneficial for poultry producers it would have to make up at least 0.4% of the diet. Another prebiotic investigated for use in poultry production is MOS. Mannose, the main component of MOS, is a unique sugar because many enteric bacteria have receptors that bind to it. These receptors, called Type 1 fimbriae, are involved in attachment of the bacteria to the cells of the host. Attachment is critical for the bacterium to be able to cause disease in the host. Chickens likely have receptors for Type 1 fimbriae in their small intestine [21]. MOS functions as a competitive binding site; the bacteria bind to it and are carried out of the gut rather than binding to the intestine. In a study that supports this theory, it was found that supplementing the drinking water of broilers with 2.5% mannose reduced Salmonella typhimurium colonization of the intestines, compared with unsupplemented control broilers [22]. Spring et al. [23] challenged 3-d-old chickens with 2 strains of Salmonella that agglutinated MOS. They found that when diets contained 0.4% MOS, chickens inoculated with either of the Salmonella strains had fewer of the bacteria in their ceca or were less likely to be colonized than the controls at d 10. Sims et al. [24] showed that MOS supplementation might be beneficial for turkey produc-
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ers. Turkeys fed diets with 0.1% MOS for the first 6 wk of life and then 0.05% for the remainder of the trial had significantly improved feed efficiency compared with the turkeys in the unsupplemented control group at 12 and 15 wk of age. At 18 wk, the turkeys in the MOS treatment group were heavier than those in the control group and had better feed efficiency, but neither of these measures were statistically significant. At 6 wk of age, but not 18 wk of age, the turkeys in the MOS treatment group had significantly less Clostridium perfringens in their large intestines than the controls. The results of the 2 studies cited here [23, 24] show that MOS could be useful for poultry producers at lower levels than FOS.
ORGANIC ACIDS Organic acids have been studied as a tool to reduce unwanted bacteria during poultry production. In some studies acids were added to the drinking water, whereas in others they were added to the feed. One study determined the effects of feeding different levels (0.5 to 0.68%) of a combination of formic and propionic acids on intestinal colonization from Salmonella received through inoculated feed [25]. They found that chickens receiving the diets containing the organic acids had a lower incidence of intestinal colonization than those chickens receiving the untreated control diets. Similarly, van Immerseel et al. [26] reported that feeding diets containing 0.3% caproic acid resulted in a significant decrease in colonization by Salmonella Enteritidis in the ceca and internal organs of chickens. Thompson and Hinton [27] reported results that may somewhat conflict with those reported in the studies mentioned above [25, 26]. They found that by adding formic and propionic acid at 0.68 and 1.2%, respectively, they reduced the total amount of acid, including lactic acid, in the crop compared with the control chickens. They concluded that their added acids (formic and propionic) could have killed some of the lactic acid-producing bacteria normally present in the crop. Chaveerach et al. [28] investigated the effect of supplemental organic acids provided through the feed or water on Campylobacter colonization. They reported that blends of acids were more effective at inhibiting the growth of
JAPR: Review Article
754 Campylobacter than the commercial products that they tested. The blends they tested included formic, acetic, and propionic acids in ratios of 1:2:3 and 1:2:5, respectively. They concluded that adding organic acids to the drinking water given to poultry could at least reduce the transmission of Campylobacter in the flock. In an in vitro study Entani et al. [29] reported that media containing 0.1% acetic acid from vinegar inhibited the growth of 17 strains of bacteria, including S. typhimurium and 8 strains of E. coli O157:H7. The media used was otherwise ideal for growing these bacteria because at 0.05% acetic acid all the bacteria grew within 2 d of plating. The results of this study suggest that the addition of vinegar to poultry feeds or the drinking water for a flock may reduce the bacterial load to which the birds are exposed or reduce the spread of bacteria within a flock. However, a further study involving poultry flocks with and without vinegar in their water or feed is needed to confirm that it would work in the field. Based on the results of these studies [25, 26, 27, 28, 29] poultry producers could consider adding organic acids such as vinegar to their feeds, but further research is required to quantify any beneficial results.
PLANT EXTRACTS Various plant extracts, especially essential oils, have been studied for their antimicrobial abilities. Most of the research done in this area has been performed in vitro, but there have been a few studies with live poultry flocks. One recent study involving live birds showed that blends of the primary components of essential oils could be used to control Clostridium perfringens, the bacterium that causes necrotic enteritis in broilers [30]. One of the 2 blends used in this study contained thymol, eugenol, curcumin, and piperin. These compounds are the principle components in the essential oils of thyme (Thymus vulgaris), clove (Syzygium aromaticum), turmeric (Curcuma longa), and black pepper (Piper nigrum), respectively. In the other blend studied, half the thymol was substituted with carvacrol, a primary component of oregano (Origanum vulgare). Some of the components and essential oils that Mitsch et al. [30] used in their study have been investigated by other research groups.
Ground thyme has been shown to inhibit the growth of S. typhimurium when added to media [31], and the essential oil of thyme has been shown to inhibit the growth of E. coli in media [32, 33, 34]. Other groups have shown thymol can inhibit the growth of S. typhimurium and E. coli [35, 36]. Eugenol, a component of the essential oil from cloves, has been shown to inhibit S. typhimurium [35]. The complete essential oil of cloves has been demonstrated to be inhibitory against E. coli [32]. In both studies, this inhibition was demonstrated in culture medium, not in live animals. The essential oil of oregano has been shown in vitro to be a strong inhibitor of E. coli [37]. However, carvacrol, a major component of the essential oil of oregano, was found to have less inhibitory activity against bacteria than the complete oil. Other research groups have shown that carvacrol can inhibit in vitro the growth of a number of different bacterial species, including S. typhimurium and E. coli [36, 38]. In vitro studies of the essential oil of black pepper have showed it to have only slight inhibitory activity against E. coli, Salmonella pullorum, and Clostridium sporogenes [39]. Another essential oil with potential applications in poultry production is that of cinnamon. Herna´ndez et al. [40] showed, in a study with live chickens, that a blend of the essential oils of cinnamon, pepper, and oregano improved some aspects of digestibility in chickens receiving supplemented feed compared with chickens fed a control diet without the blend. Cinnamon oil has also been shown in vitro to have antimicrobial activity against E. coli [37, 41]. Taken together, these studies suggest that cinnamon oil should be further studied in vivo for possible benefits in poultry production. Garlic (Allium sativum) is another plant that has been shown in vitro to have antimicrobial properties. Singh and Shukla [42] reported that the aqueous extract of garlic was a good inhibitor of 2 strains of E. coli. Similarly, Kumer and Berwal [43] found that E. coli was especially sensitive to the effects of garlic. Garlic oil has been shown to inhibit E. coli and Salmonella typhimurium in vitro [44, 45]. Further research is required to verify whether the in vitro results from these studies [42, 43, 44, 45] can be trans-
GRIGGS AND JACOB: ALTERNATIVES TO ANTIBIOTICS lated into beneficial disease-fighting results in vivo. Although the results of some of the studies investigating plant extracts may contradict one another, there seems to be a trend that suggests that plant essential oils, or at least some constituent of the oils, may have applications as antimi-
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crobials in poultry production. For many of these compounds more research with live birds is needed to determine whether they will be useful in poultry production. Thyme, oregano, and garlic should be of particular interest to producers and researchers.
CONCLUSIONS AND APPLICATIONS 1. Probiotics are a potential tool for reducing intestinal contamination with disease-causing and foodborne bacteria. They may also be useful in the prevention or treatment of coccidiosis. 2. For FOS to be noticeably beneficial for poultry producers, it would have to make up at least 0.4% of the diet. At this level, reduced “bad” bacteria and increased “good” bacteria in the microflora of the gut were observed. 3. The MOS may also be a useful tool to reduce “bad” bacteria in the gut. Lower levels of inclusion are required for MOS than for FOS. 4. Formic, acetic and propionic acids, which are organic acids, have the potential to reduce Salmonella and Campylobacter colonization in the gut of poultry. 5. Research with plant essential oils has yielded contradicting results, but there is enough evidence to suggest that they may have a role as a tool in combating bacterial diseases in poultry. Thyme, oregano, and garlic appear to have the most potential.
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