Efficient immune system development and proper digestion and absorption of feed, water, and electrolyte balance in the gut leads to the development of strong gut health in poultry. The gut ecosystem plays a vital role in eliminating toxins and infectious agents from the intestinal tract of the poultry. Many factors influence the gut microbial ecosystem, including feed additives (phytobiotics, prebiotics, probiotics, feed enzymes, organic acids etc.), feed composition, genetics, heat stress, feeding practices on the poultry farm, among others. These factors exert a substantial impact on the gut microbiota and poultry health
[22]. The association between gut health and poultry performance is widely accepted with optimal health including proper physiological functions of the intestinal tract, morphological integrity, efficient immune response, developed barrier functions, energy balance, tissue metabolism, sustained inflammatory balance and sufficient microbiota to perform desired functions in the gut. The health of poultry is influenced by the structure and functionality of gut microbiota. The progression of acquisition and maturation of the intestinal microbiota throughout the growth period of the poultry has a marked impact on the modulation of physiological functions (nutrient digestion, immunity, intestinal barrier integrity etc.) to maintain gut homeostasis and development of the intestinal epithelium. These functions are essential to optimize energy use and efficiency of extraction by the poultry birds
[2].
Consequently, it is pivotal to articulate a cost-effective approach to mitigating oxidative stress in the poultry industry. The supplementation of bioactive compounds in poultry feed improves the antioxidant ability, immunity and health performance. Cinnamon contains very active compounds, including essential oils (EOs) and phenolics, which possess potent anti-microbial, anti-inflammatory, and antioxidant activities that act as defensive agents against oxidative damage in the chicken intestinal tract.
3.2. Impact of Cinnamon on the Digestibility of Nutrients
Improved utilization of feed improves the feed conversion ratio (FCR), body weight gain (BWG) and overall health performance of broiler chicken. The stabilization of the gut microbiota ecosystem and the stimulation of digestive enzymes secretion are the two well-accepted mechanisms that play a leading role in improving feed utilization and inhibiting the growth-depressing ailments related to metabolism and digestion
[27][28][29]. The potential impacts of CNO on the secretion of digestive enzymes from the intestinal mucosa and pancreas have been described in many poultry studies
[30][31][32]. These positive impacts had been confirmed to improve the digestibility of nutrients
[31][33]. Additionally, the bioactive compounds of cinnamon affect lipid metabolism by transporting the fatty acids in the digestive tract of broilers. The CNO has positive effects on the secretion of digestive enzymes and improves the digestibility of nutrients in the gut
[34][35].
The CNO may also improve nutrient uptake by protecting intestinal gut morphology and integrity. For example, Devi, et al.
[36] reported that digestibility of nutrients was better in the cinnamon fed group. Supplementation of CNO in broilers diet increased the villus height (VH) in the duodenum and jejunum with associated increased villus surface area and the efficiency of absorption and digestion of nutrients. In addition, a greater VH means greater mucosal digestive enzyme activity, which ultimately improves the digestibility of nutrients
[37]. The increased VH was attributed to the antioxidant activity of CNO
[38]. In addition, the digestive process liberates reactive oxygen species (ROS) which act on intestinal mucosa and shorten the intestinal villi, but antioxidant enzymes (catalase and superoxide) bind the ROS. The CNO acts as hydrogen donor and exhibits antioxidant activity which protect the intestinal villi from oxidative damage by stimulating the activity of these antioxidant enzymes
[38]. CNO helps to decrease the pathogenic bacteria in the gut, which improves intestinal morphology
[39].
Cinnamaldehyde is considered a digestion stimulating agent which enhances the digestive system of broiler chicken. For example, cinnamaldehyde increased the activity of pancreatic and intestinal enzymes by provoking the secretion of salivary glands, which ultimately improved the digestion of broiler chickens
[40]. Recent studies suggested that tannins (water-soluble phenolic compounds) from cinnamon significantly impact augmenting poultry health and nutrition as they can precipitate proteins in the gut
[41][42]. The apparent ileal digestibility of nutrients, crude fat and amino acids (histidine, lysine, serine, phenylalanine, asparagine and threonine) digestibility were significant in cinnamaldehyde supplemented groups
[43]. Moreover, the inclusion of CNO in broiler diets improved protein digestion via increasing the secretion of hydrochloric acid (HCl) and pepsin in the gut. The CNO has a positive impact on the poultry digestive system by restoring the balance of the gut ecosystem and improving nutrient absorption, which could be attributed to the terpenoid compounds of cinnamon
[44]. Phytobiotic growth promoters remained active throughout the gastrointestinal tract to exert broad-spectrum anti-microbial action, enhanced nutrient utilization, and augmented intestinal histomorphology and enhanced host immunity. The CNO stimulates the secretion of enzymes and bile acid, which improves the apparent digestibility of nutrients and fat
[45][46]. The CNO play a crucial role in the interactions of feed and enzymes in the gut and influence the transit of digesta in the gut
[34]. The exact mechanism by which CNO improves nutrient digestibility in the gut of poultry is unknown and needs to be elucidated.
3.3. Cinnamon and Blood Biochemical Profile
It is established that hematological values are dependent on the physiological state of the birds. The blood biochemical profile is a vital tool that has been used to screen the impacts of nutritional, therapeutic and environmental interventions in veterinary and human medicine. Many studies have been conducted to illustrate the effect of cinnamon on blood biochemical profile, including antioxidant activity, lipid profile and immunity. The cinnamon-based PFAs group exhibited significant differences in albumin/globulin (A/G) ratio and cholesterol concentrations as compared to control treatments
[1]. Additionally, non-significant interactions were found for total protein, globulin levels and serum albumin among treatments. It was found that cinnamon-based diets played a vital role in reducing cholesterol concentrations which is highly desirable for consumers. However, it should be noted that the effects of dietary cinnamon trials on blood chemical profiles and immune system responses in poultry have not been consistent. A possible source of this variation may be related to health status of the birds. Kettunen, et al.
[47] reported that CNO supplemented diets improved the immunoglobulin A concentrations and intestinal immunocompetence which ultimately increased the performance of chicks. Recently published reports have shown that cinnamaldehyde, cinnamon powder and CNO alone or in combinations with other feed additives have a wide array of potential impacts on blood chemical profile of poultry birds.
A study conducted by Al-Kassie
[48] showed that broilers fed on 200 ppm dietary CNO had significantly lower cholesterol concentrations and heterophils/lymphocytes (H/L) ratio. In contrast, total protein, hemoglobin, red and white blood cells concentrations and packed cell volume were all increased. Moreover, Ciftci, et al.
[49] reported that serum levels of glutathione peroxidase, catalase enzyme activities, total unsaturated fatty acids, ω-6 fatty acids and phagocytic activity of blood were significantly increased in chicks fed on diets supplemented with 1000 ppm CNO. In addition, cholesterol and malondialdehyde (MDA) concentrations, alanine aminotransferase activity and total saturated fatty acid ratio were reduced in broilers fed on CNO. These authors concluded that CNO had strong antioxidant potential. Almost similar results were found by Yang, et al.
[4] who reported that MDA concentrations decreased on 21 day while serum immune globulin M (IgM) contents increased on 42 days in broilers. In another study, Mehdipour and Afsharmanesh
[50] found that dietary cinnamon powder significantly increased total superoxide dismutase activity, total antioxidant capacity, corticosteroid and catalase on day 42 of the study. The concentration of MDA was reduced in the cinnamon fed group. Kanani, et al.
[51] investigated the impact of cinnamon powder on blood parameters of broiler chicks (Ross 300) under heat stress. They reported that the concentration of MDA, lactate dehydrogenase and blood uric were decreased. While, there were no effect on blood sodium, urea, chlorine, potassium, creatinine and aspartate aminotransferase among all treatments. Naderi, et al.
[52] found that inclusion of cinnamon and turmeric in broilers diet lowered the heterophil to lymphocyte ratio leading them to suggest that dietary cinnamon and turmeric can be used as potential stress alleviators and alternatives to AGPs. Furthermore, Toghyani, et al.
[53] found that serum glutamic pyruvic transaminase (SGPT) enzyme was reduced but serum glutamic oxaloacetic transaminase (SGOT), serum total protein, albumin and triglycerides were not changed among the treatments. These outcomes are due to the antioxidant potential of cinnamaldehyde which helps to protect the liver from reactive oxygen species.
Broiler chicks supplemented diet with CNO had significantly decreased circulating cholesterol, low-density lipoprotein (LDL) and triglyceride concentrations, whereas high-density lipoproteins (HDL) were increased
[54]. Similar observations were made by Najafi and Taherpour
[55] who showed that 0.8% dietary cinnamon reduced plasma cholesterol, LDL, total proteins and blood glucose concentrations. In another study, Hossain, et al.
[56] found that 1.0% cinnamon powder increased the antibody SP ratio (ratio of sample to positive control) for Newcastle disease and lowered blood glucose concentrations. Furthermore, dietary cinnamon and zinc decreased blood glucose and triglyceride concentrations under cold stress conditions
[57]. However, there was no effects of diet on plasma cholesterol, albumin and uric acid concentrations. In another study, thiobarbituric acid, LDL and glucose concentrations were decreased in pigs supplemented with cinnamon although plasma cholesterol and triglycerides concentrations were unchanged
[58].
Moreover, inclusion of dietary cinnamon significantly increased serum immunoglobulin levels in broilers
[59]. Furthermore, poultry fed a diet contaminated with
Clostridium perfringens and supplemented with cinnamaldehyde, thyme, anise, yucca extract, carvacrol and oregano essential oils (OEOs) exhibited no significant effect of diet on circulating total protein, albumin and glucose concentrations and aspartate aminotransferase activity
[60]. Lee, et al.
[29] found that inclusion of cinnamaldehyde in broiler diet had no significant impact on plasma lipid concentrations. In summary, the consensus is that the reduction of peroxidation and free radicals’ formation by cinnamon bioactives’ action ultimately diminishes oxidative stress in broilers.
3.5. Effect of Cinnamon on the Gut Microbiota
It is likely that the desired optimal health and performance of poultry can be achieved via modulating the intestinal microbiota and their functions with suitable dietary strategies
[65]. So, PFAs are considered potential agents to improve chicken health by establishing a balanced gut ecosystem. PFAs are considered as quintessential feed additives in the poultry industry since there are no residue or toxin issues. Among the PFAs, phytobiotics are used to modulate the poultry gut ecosystem via generating anti-microbial, anti-inflammatory, and antioxidant responses, increasing the optimum nutrient absorption in the gut system
[66]. To meet the market demand for poultry meat, broilers are reared to reach their maximum weight in the shortest possible time. Therefore, gut microbiota plays a crucial role to maintain the productive interactions between the host and the gut. In the intestinal ecosystem, the digestion and absorption of many nutrients takes place in the small intestine while the cecum is the site which is densely populated with a range of bacteria which are primary responsible for the fermentation of nutrients not absorbed at the ileum
[67]. The chicken ileum is predominant with microaerophilic bacteria (
Enterococcus spp. and
Lactobacillus spp.) while the cecum nurtures the pathogenic obligate anaerobic bacteria (
Campylobacter spp. and
Enterococcus spp.)
[68][69]. The intestinal ecosystem has been proposed as being closely related to poultry performance. However, very few studies have investigated the relationship between phytobiotic dietary modulation, intestinal bacteria and health and performance of poultry. Nevertheless, the next section will discuss a possible strategic approach to improve health performance through modulating the gut ecosystem and relevant gut bacteria.
The inclusion of dietary cinnamon bioactive compounds contributes to producing and maintaining gut microflora and digestive functions in poultry
[35]. The dietary cinnamon promoted the growth of beneficial bacteria while reducing the pathogenic bacterial load as compared to the control groups
[1]. They found that dietary cinnamon increased the growth of
Lactobacillus spp. while inhibiting
Campylobacter spp. and
E. coli in the ileum and cecum of poultry. The production of SCFAs are attributed towards the
Lactobacillus spp. fermentation which are responsible for the maintenance of gut ecosystem and preventing the pH-sensitive pathogenic bacteria. The bioactive compounds of cinnamon have potential anti-microbial activities against
Enterococcus faecalis,
Vibrio parahaemolyticus,
Pseudomonas aeruginosa,
Salmonella spp.
Klebsiella pneumoniae,
Staphylococcus epidermis,
Staphylococcus aureus and
E. coli [70]. For example, the CNO inhibited the action of Gram-negative bacteria;
Enterobacter cloacae,
E. coli,
Pseudomonas aeruginosa, and
Alcaligens faecalis and Gram-positive bacteria;
Micrococcus leteus,
Staphylococcus aureus,
Enterococcus faecalis, and
Bacillus cereus, the fungi;
Rhizopus oligosporus and
Aspergillus niger, and the yeast;
Candida albicans [71].
The proportions of commensal and pathogenic bacteria in the poultry gut system should be balanced to achieve optimal animal health and productivity. The potential anti-microbial and antioxidant effects had been reported in many studies
[4][50]. The CNOs, including cinnamaldehyde, carvacrol, thymol, etc. showed powerful antioxidant and anti-microbial activities against
Salmonella and
E. coli [72]. The inclusion of CNO in broilers diet had significantly increased
Lactobacillus and
Bifidobacteria in the cecum while reduced the
E. coli relative multiplicity on 42 day reported by Yang, Zhao, Shao, Liao, Zhang, Lu and Luo
[4]. They suggested that dietary CNO can be used as an effective alternative to AGPs to improve gut microbiota in the cecum of broilers. Similar results were observed by
[50], who found that the inclusion of 200 ppm/kg dietary CNO increased the numbers of
Lactobacillus in the ileum while decreasing the
coliforms as compared to the other groups. The CNO exhibited more potent anti-microbial results as compared to the extract against bacteria and fungi where the lowest minimum inhibitory concentration (MIC) (1.25%
v/v) was reported against
E. coli,
Klebsiella spp.,
Bacillus spp. and
Listeria monocytogenes as well as
Rhizomucor spp. among the fungi
[73]. Concomitantly, they concluded that MIC and minimal bactericide concentration for CNO were between 25–100 and 125–250 ug/mL, respectively.
Moreover, Pathak, et al.
[74] reported that supplementation of cinnamaldehyde and formic acid in broilers diet did not exert any effect against total bacterial counts of
E. coli and
Lactobacillus. However,
Clostridium and
Salmonella counts were reduced in the ileal and caecal contents as compared to the other groups. Additionally, cinnamaldehyde and formic acid were more effective against
Clostridium genus in the small intestine and caecum of broilers.
The counts of
E. coli and
Clostridium spp. were lower in the pre-caecal contents of broilers supplemented with CNO while
Lactobacillus spp. were unchanged
[37]. The proliferation of pathogens in the gut can be prevented by using cinnamaldehyde and thymol in poultry diet
[75]. These authors reported that a blend of cinnamaldehyde and thymol reduced the
E. coli counts in the caecum, possibly due to the capacity of CNO to disrupt the bacterial cell membranes. Additionally, the CNO stimulates mucus release in the intestinal tract, which in turn reduces the adhesion of pathogens to the epithelial cells in the gut
[31]. Bacterial counts increase with age in the small intestine with the predominant species being
Streptococci,
Lactobacilli,
Enterobacteria,
Eubacteria and
Fusobacteria. On the other hand, the gram-positive
Bacteroides, Cocci,
Eubacterium spp.,
Lactobacillus spp.,
Clostridium spp., and
Fusobacterium spp. predominate in the anaerobic caecum of broilers
[76].
Furthermore, Jamroz, et al.
[77] reported that broilers supplemented with cinnamaldehyde, carvacrol and capsaicin had higher
Lactobacillus counts in the gut while fungi,
Clostridium perfringens and
E. coli counts were reduced. The use of trans-cinnamaldehyde in in-vitro fermentations reduced Clostridium jejuni and Campylobacter concentrations after 8 h of incubation
[78] without exerting any detrimental effect on natural gut microflora. Additionally, CNO has greater potency against
E. coli and
Salmonella typhimurium than the other EOs
[79]. The largest and most abundant bioactive compounds in cinnamon are the volatile compounds: cinnamaldehyde, eugenol, carvacrol, condensed tannins and other polyphenolic compounds perform antioxidant, anti-microbial and anti-inflammatory activities in the poultry gut. The anti-microbial potential of cinnamaldehyde, carvacrol and eugenol were detected due to their preemptive effects against harmful microorganisms
[80]. Furthermore, carvacrol can manipulate the pH equilibrium of inorganic ions by disrupting the membrane integrity of the gut
[81]. On the other hand, herb and spice extracts can stimulate the growth of beneficial bacteria while inhibiting the growth of pathogenic bacteria in the intestinal tract of the broilers
[82].
Many plant bioactive compounds are used as feed additives to improve poultry health and growth performance. These additives modulate the gut microflora of broilers to enhance nutrient availability and uptake in the gut, immune health, and inhibition of pathogenic microorganisms. The antibacterial and antifungal potential of
C. bejolghota bark oil was firstly examined against Gram positive, Gram negative bacteria and
Colletotrichum spp. fungi. The MIC of CNO against fungal pathogens was 125–500 μg/mL while it was 31.25 to 62.50 μL/mL against bacteria. The potent anti-microbial activity of
C. bejolghota EO was associated mainly with compounds such as terpinen-4-ol, 1,8-cineole, borneol, linalool, and γ-terpineol
[83]. Orengo, et al.
[84] reported that inclusion of cinnamaldehyde in broilers diet reduced
Eimeria aceryulina oocyst infection and decreased gross lesion scores compared with other groups. It is believed that CNOs may help reduce stress during critical conditions and stimulate a strong immune defense system, which results in improved gut health and better growth
[38]. Dietary CNO supplementation has the potential to reduce the rate of
Eimeria oocyst shedding and act as a therapeutic anticoccidial agent in poultry
[85].
Cinnamon is abundant with flavonols
[12][15][86][87] which have strong antioxidant and anti-microbial properties. Among flavonols, quercetin was reported to inhibit bacteria growth, such as
Salmonella enterica serotype
Typhimurium,
E. coli,
Staphylococcus aureus, and
Pseudomonas aeruginosa in the poultry gut. Thus, the quercetin compounds enhance performance and health by modulating the gut ecosystem of poultry birds
[23]. Cinnamon anthocyanins have potential effects on poultry health as they act as phyto-pigments in plants. They have potential as anti-inflammatory, antidiabetic, anticancer biochemical agents, anti-obesity, immunomodulatory and antioxidant agents; thus, inclusion of anthocyanins produce various health benefits in the gut of heat stressed broilers
[5]. Proanthocyanidins with a degree of polymerization less than three are depolymerized into catechin and epicatechin mixtures of monomers and dimers absorbed from the small intestine.
Additionally, the PAs with more than 10 degrees of polymerization are not absorbed from the small intestine and pass into the large intestine, where they are degraded by the microflora
[88]. Although PAs exhibit low absorption from the small intestine, they can still deliver health benefits
[89]. Proanthocyanidins such as procyanidin A and procyanidin B2 are metabolized by gut flora to produce phenolic acids and other metabolites and are detected in urine. It is suggested that these phenolic acids may have health effects in the gut
[90]. A variety of gut micro-flora, particularly Bacteroides spp. and Eubacterium spp., may contribute to the metabolism of polyphenols, especially flavonoids
[90]. Furthermore, anthocyanins and their metabolites regulate the intestinal tract by improving
Lactobacillus spp.,
Enterococcus spp.,
Bifidobacterium spp. in the poultry gut. Anthocyanins suppress the growth of pathogenic bacteria and improve the organ functionality of poultry and may potentially ameliorate against heat stress
[23].
Flavonoids, including those found in cinnamon, act as anti-microbial agents in the poultry gut
[23][91]. The composition of cinnamon has also been investigated by other research groups who found that cinnamon bark containing high concentrations of tannins including 3.6% epicatechins and 23.2% PAs
[21]. Tannin compounds increase the
Firmicutes and
Bacteroidetes in the cecum of broilers and support the growth of
Lactobacillus by inducing the iron-poor environments in the gut as
Lactobacillus bacteria do not need iron for their full proliferation and growth. In addition, tannin compounds reduce the
Bacteroides by decreasing the production of acetate and propionate in the intestinal tract of chickens. The production of SCFAs in the poultry gut is associated with tannic acid
[23][41]. Anderson, et al.
[92] reported that condensed and hydrolyzable tannin-rich extracts have strong anti-microbial activity against
Campylobacter jejuni. The ethanolic extract of cinnamon has strong anti-microbial activity against
Salmonella aureus strains as reported by Bonilla and Sobral
[93]. Overall, the effect of cinnamon on gut microbiota of poultry birds given in
Table 1.
Table 1. Effect of cinnamon on gut microbiota of poultry birds.
Feed Composition |
Bird Type |
Feed Level |
Gut Microbiota |
Gut Part |
Ref. |
* Cinnamon powder |
Broiler |
10% cinnamon |
Total counts of Enterococcus spp. and Lactobacillus spp. ↑ Campylobacter spp. and E. coli ↓ |
Ileum and cecum |
[1] |
CNO |
Broiler |
100 mg/kg |
Lactobacillus and Bifidobacterium ↑ E. coli ↓ |
Cecum |
[4] |
CNO |
Broiler |
300 mg/kg |
No change in Lactobacillus spp.; E. coli and Clostridium spp. ↓ |
Cecum |
[37] |
CNO |
Japanese quail |
200 mg/kg |
Lactobacillus ↑ Coliforms count ↓ |
intestine |
[50] |
* CNO |
Broiler |
500 mg/kg |
No effect on total bacterial counts, E. coli and Lactobacillus; Clostridium and Salmonella counts ↓ |
Ileum and cecum |
[74] |
* Cinnamaldehyde |
Ross broiler |
5 g + 15 g/tonne |
E. coli ↓ |
Cecum |
[75] |
* Cinnamaldehyde |
Hubbard broiler |
100 mg/kg |
Lactobacillus counts ↑, E. coli and Clostridium perfringens↓ |
Ileum and cecum |
[77] |