There are many factors such as dietary and management which, have been shown to markedly affect the structure and activities of gut microbial communities in livestock animals. Under stressed conditions, direct-fed microbials may be used to reduce the risk or severity of scours caused by disruption of the normal intestinal environment. . Prebiotics are nondigestible dietary ingredients, usually oligosaccharides (OS), which provide a health benefit to the host by directly modulating the gut microbiota. The observable benefits of prebiotics may also be minimal in generally healthy calves In coming days, it is expected that prebiotics could be the part of diets in both ruminants and non-ruminants for enabling modulation of gut microfloravis a vis animals productivity in ecological ways. This review mainly focused on the benefits of probiotics/prebiotics on the GI microbial ecosystem in ruminants, which is deeply involved in nutrition and health for the animal. However, it is necessary to conduct more research with prebiotics as feed additives to understand the detailed mechanisms of action and identify better alternatives for animal production and health.
It is well known that dairy calves are future herd. So the performance of the calf is totally dependent on the managemental practices during first three months. It plays a key role in the economy of dairy farms because they increase operating costs and reduce long-term productivity of the animal. Hence, the maintenance of calf health and optimizing calf growth are key objectives especially at early stages of life (Ghosh and Mehla, 2012).The dairy calf encounters potentially stressful situations in its first few months of life such as weaning, and commingling. Stress can lead to suppression of the immune system and increase the risk of disease in the presence of a pathogen (Salak-Johnson and McGlone, 2014).Weaning calves suffer from stress of digestive tract upset because of the shift from a liquid to a solid diet and change in digestive tract microflora. This diet transition sometimes results in establishment of less desirable intestinal microflora leading to poor performance (Bach et al., 2011). Further, there are more disturbances in rumen microbiota by use of various antibiotics for combating the tract infection. In extension the commingling phase of a dairy calf’s life, the transition from individual housing to group housing, has been shown to increase the risk of bovine respiratory disease, decrease leukocyte function, and decrease average daily gain (Hulbert and Ballou, 2012). These disease and conditions are so stressful that calf is sometimes unable to cope up and may lead to mortality or stunted growth in future life. So to overcome these situations various preventive measures as well treatments are practiced. In recent years there have been many advances in the prevention and treatment of calf problems. Here at this point nutritional quality of a feed needs to be improved. As nutritional quality is not only influenced by nutrient content but also by many other aspects such as, hygiene, content of anti-nutritional factors, digestibility, palatability and effect on intestinal health. Hence, the use of feed additives has been an important part of achieving this success (Fanelli, 2012).Feed additives are materials that are used to enhance the effectiveness of nutrients and exert their effects in the gut or on the gut wall cells to the animal (McDonald et al.,2010). A large number of feed products as additives are available to prevent scours and promote gut health and animal growth rates. They are used for the purpose of promoting animal growth through their effect in increasing feed quality and palatability (Fanelli, 2012). The actual benefits of these products are hard to quantify, but clearly they modify and protect the gut health in periods of stress and disease. There are a number of feed additives that are used in animal feeds such as antibiotics, probiotics, oligosaccharides, enzymes and organic acids. Along with this the most common milk additives are probiotics, prebiotics, rennet, sodium bentonite, antibiotics, vitamins and minerals (Schouten, 2005).
Since long time among the various feed additives antibiotic is the most frequently and extensively used in livestock diets due to its therapeutic importance (Cho et al., 2011). Antibiotics helps in checking diarrhoea and enhance body weight gain by modifying gut microflora in growing calves (Novak and Katz, 2006).But the growing concern of the consumers for clean and safe products have restricted the use of antibiotic as feed additive as growth promoters. Hence this led to initiation of many alternative strategies for maximizing production by maintaining the animals health and performance. At the same time maximizing health and well-being of the animals and minimize the impact of the industry on the environment (Fanelli, 2012). Among feed additives prebiotics as a natural additive can be used as an alternative to antibiotics maintain optimum ruminal digestion of feed.
The Introduction of Prebiotics
Prebiotics are defined as ‘non-digestible food ingredients that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon that can improve host health’ (Gibson and Roberfroid, 1995). Prebiotics are selectively fermented, dietary ingredients that result in specific changes in the composition and/or activity of the gastrointestinal microbiota, thus conferring benefit(s) upon host health. Unlike probiotics, prebiotics target the microbiota already present within the ecosystem, acting as a ‘food’ for the target microbes with beneficial consequences for host (Hardy et al., 2013). The use of prebiotics is a promising approach for enhancing the role of endogenous beneficial microbiota in the gut. One of the reasons prebiotics are effective is because they are resistant to gastric acidity, absorption, and hydrolysis by enzymes produced in the gastrointestinal tract (Patel and Goyal, 2012). They are, however, fermented by intestinal microflora which promotes proliferation of commensal microorganisms. Lactobacilli and Bifidobacteria are the most common microbial target genera in prebiotics application. A growing interest exists in the health-promoting benefits of prebiotics. Multiple mechanisms of action for prebiotics have been postulated, particularly enhancement of probiotic growth in the gut (Macfarlane et al., 2006). Bifidobacteria produce various glycosidases which are enzymes that hydrolyze glycosidic bonds of polysaccharides like most prebiotics, hence prebiotics’ ability to be readily fermented (Russo et al., 2012). The fermentation products of prebiotics by intestinal microflora also provide benefit by immune modulation, improved energy efficiency and digestibility, and decreased intestinal pH which suppresses pathogenic bacteria (Mizota, 1996; Roodposhti and Dabiri, 2012). Prebiotics themselves have a positive influence on immune parameters in the gut-associated lymphoid tissues, secondary lymphoid tissues, and peripheral circulation (Bodera, 2008). Prebiotics may promote T Helper 1 and regulatory T cell-dependent immune responses over T helper 2 responses (Patel and Goyal, 2012). Types of prebiotics used in the livestock industry include indigestible sugars, ex. fructooligosaccharides (FOS), galactooligosacchardies, mannan oligosaccharides, beta glucans, inulin and lactulose (Gibson et al., 1995; Kleesen et al., 2001).All the above probiotics have their own function and are helpful in improving the health and performance of calves.
Production and Composition
Mannan oligosaccharides are short-chain, low molecular weight carbohydrate fragments of the yeast cell wall, particularly Saccharomyces cerevisiae. Mannans represent approximately 30% of the cell wall weight and are found on the outer parts of the cell wall (Kollár et al., 1997). They are comprised of many α-1, 2 and α-1, 3 N-linked glycan side chains attached to a α-1, 6 linked mannose monomer backbone (Kollár et al., 1997). To obtain these cell wall derivatives, yeast cells are lysed and the yeast culture that is obtained is centrifuged to isolate the cell wall components. The cell wall components are then washed and spray dried (Spring et al., 2000). The most important antigenic component of the cell wall are the mannans of the yeast cell surface (Ballou, 1970).
One of the primary functions of mannan oligosaccharides is to provide competitive binding for gram negative bacteria. Gram negative bacteria have mannose-specific type-1 fimbriae that attach to D-mannose receptors on the epithelium of the gastrointestinal tract (Friman et al., 1996; Ofek et al., 1977). The presence of mannan oligosaccharides can provide an alternate binding site for these pathogens which then block them from colonizing the epithelium and the complex exits the tract without causing harm (Spring, 2000).Mannanoligosaccharides have the ability to alter the composition of the intestinal flora, transport time, digestibility, absorption, and intestinal health of calves in this way (McGuirk, 2008). Improved intestinal health and the inhibition of pathogenic microbes may contribute to smaller fecal scores and fewer incidence of scours. Pathogenic bacteria produce toxins that cause intestinal hyperactivity, secretion, and diarrhea (Giannella, 1983). In addition to competitive binding, mannan oligosaccharides may also promote immune function such as phagocytosis and oxidative burst (Magalhães et al., 2008). A potential mechanism for the immunomodulatory effects of mannan oligosaccharides was described by Franklin et al., 2005. The authors proposed that collectins may be responsible for this immunomodulatory function. One of the three types of collectins present in cattle are mannose-binding proteins that can bind to mannose, N-acetylmannosamine, or N-acetylglucosamine. Mannanoligosaccharides may promote the production of these mannose binding proteins. After binding, this complex can act as an opsonin and improve phagocytosis or activate thecomplement system (Neth et al., 2002).
Production and Composition
Beta glucans are other carbohydrate components of the yeast cell wall of Saccharomyces cerevisiae. Beta glucans are also components of fungi and cereal grains like barley and oats (McGuirk, 2010). Beta glucans are glucose polymers consisting of β-1, 3 and β-1, 6 linked D-glucopyranosyl units (Wang et al., 2008).They account for 50 to 60% of the yeast cell wall weight. In contrast from mannan oligosaccharides, glucans are found towards the inside of the cell wall. They provide structure and rigidity to the cell wall that allows organization of the other cell wall components (Kollár et al., 1997). The efficacy of beta glucans may be modulated by the degree of branching, the molecular mass, and the tertiary structure (Russo et al., 2012).
Beta glucans that are large in molecular weight have been found to directly affect phagocytic, cytotoxic, and antimicrobial activities of leukocytes, particularly macrophages. They also promote oxidative burst responses by helping to produce reactive oxygen and nitrogen intermediates and clear apoptotic cells by up-regulating the FS receptor (Gantner et al., 2005; Brown and Gordon, 2003). In addition to promoting innate immune responses, betaglucans increase production of proinflammatory cytokines and chemokines. Cytokines and chemokines stimulated by beta glucan-activated cells include IL-1β, IL-6, and TNF-α (Vetvicka and Yvin, 2004). These cytokines and chemokines aid in the recruitment of additional leukocytes to the site of infection.
The mechanism by which beta glucans can stimulate these immune responses is credited to the Dectin-1 receptor. The Dectin-1 receptor is expressed on monocytes, macrophages, neutrophils, dendritic cells, and splenic T cells and can recognize carbohydrates with β-1,3 andβ-1,6 glucan linkages (Sonck et al., 2009). When beta glucan binds to Dectin-1, the motif becomes phosphorylated, which sends a signal to induce phagocytosis and respiratory burst (Brown and Gordon, 2003). On the other hand, cytokine and chemokine production may be attributed to Toll-like receptor 2 (Brown and Gordon, 2003). To produce TNF-α and IL-12, both Dectin-1 and Toll-like receptor 2 were required. TNF-α has many functions, one of them being to aid in the oxidative burst response of neutrophils.IL-12 is important in stimulating production of IFN-γ and promoting the T helper 1 immune response (Manetti et al., 1993).
Production and Composition
Inulin is a natural b-(2-1)-linked fructo-oligosaccharide with up to 60 units common in plants used in the Western diet (Van Loo et al., 1995).Inulin belong to a class of carbohydrates known as fructans. The main sources of inulin that are used are chicory and Jerusalem artichoke. Purified inulin can also be produced from tubers of the Jerusalem artichoke or Chicory. It contains 6–10% sugars, such as glucose, fructose and sucrose, which are native to the chicory roots (Niness, 1999). Inulin belongs to the fructan group. This consists of fructose subunits linked by β-2, 1 bonds containing, at the reducing end, a single molecule of glucose. Glucose is linked by α-1, 2 bonds to a fructose chain (Kolida and Gibson, 2007). β-2,1- linkages not only determine the specific properties of inulin, but also protect it from digestion in the upper part of GIT (gastrointestinal tract) and are responsible for its reduced caloric value and the effect of dietary fiber (Niness, 1999).
Inulin has effects on immune system either directly or indirectly. An indirect effect of inulin as prebiotics is to the stimulation of the development of beneficial gut microbiota strains, and the inhibition of the proliferation of pathogenic bacteria. This causes changes in composition of the intestinal microfloral population like by increasing the number of bifidobacteria, there will be increased competition with pathogenic bacteria for binding sites on the intestinal epithelium and for nutrients, thus inhibiting survival of the pathogenic strains. Further the beneficial gut microbiota bacteria may also cross the intestinal barrier into the Peyer’s patches, and activate immune cells there (Berg, 1985).However, the direct effect involves the stimulatory effect on phagocytosis carried out by the phagocytic cells in blood (Wójcik et al., 2007), as well as non-specific mechanisms of humoral immunity (Milewski et al., 2007).
Inulin also helps in production of Short Chain Fatty Acids (SCFA)from the fermentation of dietary fiber which also have significant impact on the immune system by acidification of the colonic environment, acidification of the colon favoring mucin production as well as binding to SCFA receptors on immune cells within the gut-associated lymphoid tissues(GALT) (Lomax and Calder, 2009).The increased concentration of SCFA results in a higher number (Kelly-Quagliana et al., 1998) of natural killer (NK) cells and stimulates their activity. It is believed that inulin enhanced with oligofructose (OF) causes beneficial changes in the immune function of GALT (Roller et al., 2004).It has been found in the earlier studies that inulin enriched with oligofructose enhances the cytotoxicity of NK cells produced in the spleen, intensifies cytokine production by spleen cells, and has stimulating properties on the immune response to carcinogenic agents (Watzl et al., 2005).
Lactulose is a semi-synthetic disaccharide (Schumann, 2002) that is mainly fermented by beneficial bacteria like lactobacilli or bifidobacteria (Mitsuoka et al., 1987). Lactulose a “bifidus factor” is composed of galactose and fructose, which can be produced by the isomerization of lactose. It is a prebiotic carbohydrate which stimulates the growth of health-promoting bacteria in the gastrointestinal tract, such as bifidobacteria and lactobacilli and at the same time inhibits growth of pathogenic bacteria such as Salmonella. Lactulose is generally prepared from an alkaline solution of lactose. The glucose (Glu) moiety of lactose is isomerized to Fru, leading to the lactulose production. Different reactions and schemes for the production of lactulose have been developed. Not only chemical isomerization, but also enzymatic isomerization methods utilizing b-galactosidases have been developed (Schuster-Wolff-Bühring et al., 2010).
Lactulose as a prebiotics have a positive effect on feed intake and body weight in calves. It has been reported that the average daily milk replacer intake in pre weaned calves was significant higher in feeding group with lactulose. An increased intake of crude protein and energy was achieved in calves, due to the feeding of lactulose. Further a positive trend ongrowth was observed with increase average daily gain (ADG) (Fleige et al., 2007). In addition it was also reported that here was significantly increased feed consumption and a tendency for improved daily weight gain for calves fed 3% lactulose and a probiotic bacteria strain with their milk replacer (Fleige et al., 2007). In accordance to the longer villi lactulose also tended to increase the number of proliferative cells in ileum. Lactulose alters the microbial balance and the biochemical composition of caecal contents in animals. Several in-vivo studies have demonstrated that lactulose favours the growth of gram positive cocci and rods mostly belonging to the genera Bifidobacterium and Lactobacillus (Bouhnik et al., 2004), while bacterial counts of galactosidase- negative microorganisms like subspecies of the genera Clostridium and Bacteroides have been shown to decrease (Hoffmann and Bircher, 1969; Mizota et al., 2002). In extension metabolism of lactulose leads to an enhanced production of acetic acid, lactic acid, gas, short chain fatty acids (SCFA) and the caecal pH has been shown to drop down to pH-values of about 5.0 (MacFarlaneet al., 2006). Further lactulose increased permeability of intestinal mucosa and an enhanced solubility of minerals in the colon at low pH (MacFarlane et al., 1991; Seki et al., 2007).
Effects of Prebiotics on Calf Performance
Dairy calf performance is important for productivity later in life. Prebiotics have been shown to improve performance measures such as average daily gain, feed intake, and digestibility. Prebiotics mainly used in calves feeding have carbohydrate as main nutrient which produces volatile fatty acids, which further may increase nutrient digestibility and subsequently increase feed efficiency. However, in a study conducted with calves fed mannan oligosaccharides, no differences in volatile fatty acid production were observed (Hill et al., 2009) and no differences were seen in dogs supplemented with fructooligosaccharides or mannan oligosaccharides (Swanson et al., 2002).
In a study, calves supplemented with beta glucan had increased rumen pH and nutrient digestibility (Kim et al., 2011). Mannan oligosaccharides (MOS) have improved performance in nursery pigs (Dvorak et al., 1998) and weight gain and grain intake in dairy calves (Dvorak and Jacques, 1997). In addition, investigation continues into the potential relationship between oligosaccharides and human intestinal function (Jenkins et al., 1999) and their role in modulation of human gastrointestinal microflora (Gibson, 1999).Increased average daily gain in weight and a tendency for improved feed efficiency in calves was also found when fed galactosyl-lactose in milk replacer (Quigley et al., 1997). Similarly, an increase in body weight gain per calf per day, feed intake per calf per day, and feed conversion efficiency were observed by Ghosh and Mehla (2012) when calves were administered 4 g/d of a mannan oligosaccharide supplement. Although feed cost per calf per day was increased with prebiotic supplementation, these costs were off-set by the increases in performance. Studies comparing prebiotic supplement to antibiotics, found no differences in overall body weight gain, feed intake, or feed efficiency, indicating that prebiotics may be a viable alternative for prophylactic antibiotic use (Donovan et al., 2002). The synthetic disaccharide lactulose feeding has the tendency to increase growth performance of preruminant calves and improves the intestinal microflora by stimulating the growth of selected probiotic bacteria in the gut. In a trial conducted by Fleige et al. (2007), it was found that the average daily live weight gain tended to be higher for group fed with lactulose at the rate of 3% (1350 g/day) than group with no lactulose (1288 g/day). There is evidence that prebiotics may modulate feeding behavior, indicated by results of studies showing improved body weight gain or feed intake. In addition, studies have shown that prebiotic-supplemented calves increase intake at a faster rate than un-supplemented calves (Heinrichs et al., 2003; Terré et al., 2006; Morrison et al.,2010).
Feeding fructooligosaccharides enhances the growth performance of veal calves by decreasing feed conversion ratios and increasing carcass weight (Grand et al., 2013).There is down regulation of mRNA expression of genes involved in inflammation in the intestine of the preruminant calves when they are supplemented milk with the prebiotics inulin and lactulose (Masanetz et al., 2011). Prebiotics have pronounced role in many minerals absorption and transportation. Prebiotics increase the production of Short Chain Fatty Acids (SCFA) which shift the lumen pH towards acidic and, thereby increasing the solubilisation of minerals. Butyrate acts as an energy source for intestinal epithelial cells and improves their absorptive capacity.
Generally, prebiotics increase the absorption of Ca, Mg, Fe, Zn and Cu. They also increase the absorption of Na+ and colonic water. Other researchers have observed an increased capacity of calcium transporters (calbindin) in the colon (Ohta et al., 1998). Agave fructansas prebiotics prevents bone loss and improves bone formation (Garcia-Vieyra et al., 2014).Further it was seen that the iron bioavailability in corn and soybean meal was increased due to prebiotic supplementation (Yasuda et al., 2006).
Effect of Prebiotics on Calf Health
Prebiotics such as mannan oligosaccharides prevent attachment of pathogenic bacteria whereas mannan oligosaccharides and beta glucanscan improve the immune system of the calf. (FOS) in combination with spray-dried bovine serum to calves reduced the incidence and severity of enteric disease (Quigley et al., 2002). It has been suggested that this sugar prevents the adhesion of Enterobacteriaceae, most notably Escherichia coli and Salmonella, to the intestinal epithelium (Heartmink et al., 1997). Supplementation of MOS, FOS, and GL may improve the growth performance of calves in both the pre- or post weaning stage.
Indeed many studies have shown an increase in normal fecal scores and a decrease in the incidence of scours with prebiotic supplementation. Pre-weaned calves fed milk replacer supplemented with mannanoligosacchardies reported to have a good fecal scores compared with calves that received no supplement (Heinrichs et al., 2003). Dairy calves fed a yeast culture derived from Saccharomyces cerevisiae had more incidences of normal fecal scores and had fewer incidences of fever, diarrhea, and health disorders as compared to controls (Magalhães et al., 2007). Furthermore, Ghosh and Mehla (2012) reported that a mannan oligosaccharide supplementation reduced fecal coliform counts. Prebiotics may exert cancer protective effects at the cellular level following SCFA formation. SCFA induce apoptosis in colon adenoma and cancer cell lines (Hague et al., 1994).
Lactulose has an effect on the morphology of intestine. It was found that there was a reduction of ileal villus height and decrease in the depth of the crypts when compared with control, due to lactulose treatment of approximately 14% lactulose fed group (L1) and 20% lactulose fed group (L3). (Fleige et al., 2007)
Effect of Prebiotics on Immune Function
The administration of prebiotics has been associated with immunomodulatory effects encompassing innate, adaptive immunity as a result of the interaction with the microbiota (Gibson, 2008). Most information about the effects of prebiotics on the immune system comes from experimental trials with inulin and FOS. Prebiotics act like growth factor to particular commensal bacteria, which inhibit the adherence and invasion of pathogens in the colonic epithelia by competing for the same glycoconjugates present on the surface of epithelial cells, altering the colonic pH, favoring the barrier function, improving the mucus production, producing short-chain fatty acids and inducing cytokine production (Korzenik and Podolsky, 2006). The gut-associated lymphoid tissue (GALT) is the biggest tissue in the immune system comprising 60% of all lymphocytes in the body. It contains Peyer’s patches (PP), lamina propria (LP) and intraepithelial lymphocytes (IEL) forming a unique immune network (MowatandViney, 1997). PP contains follicle-associated epithelium (FAE) that covers M-cells responsible for transporting the antigen onto the lymphatic tissue where dendritic, Tand B-cells are found (Mowat, 2003). LP is the region between the epithelium and the muscle and contains mast cells, dendritic cells, macrophages and B- and T-cells (MacDonald, 2003). The consumption of prebiotics can modulate immune parameters in GALT, secondary lymphoid tissues and peripheral circulation (Bodera, 2008). Necrotizing enterocolitis (NEC) is a major cause of morbidity and mortality in premature infants. Prebiotic administration manipulates the intestinal bacterial community, accelerating the growth of commensal bacteria. Prebiotic supplemented formula increase stool colony counts of bifidobacteria and lactobacilli in preterm neonates without adversely affecting weight gain (Srinivasjois et al., 2009). FOS is being increasingly included in food products and infant formulae due to their laxative effect. Their consumption increases faecal bolus and the frequency of depositions, reducing instances of constipation, considered one of the growing problems associated with inadequate fiber diet consumption in the modern society and neonates (Sabater-Molina et al., 2009). There are sufficient experimental data to support the hypothesis that prebiotic mixture substantially contributes to the improvement of infant formulae. The immune-modulatory effect of specific prebiotic oligosaccharides viz. GOS, FOS and pectin-derived acidic oligosaccharides was studied. The supplementation exerted immunemodulatory effect during the early phase of a murine immune response(Vos et al., 2010).They also seem to promote a positive modulation of the immune system (Delgado et al., 2011).
Lactulose feeding had an immunomodulatory effect on the composition of T-cell subsets in different immune compartments and had minor effects on pro- and anti inflammatory cytokine mRNA expression. A significantly greater number of blood lymphocytes were detected in the 3% lactulose group than in the control group. The expression results in male calves indicated that the transcription of IgA Fc receptor in the ileal mucosa of the 1% lactulose treatment group increased significantly and also tended to increase in the 3% lactulose group. Furthermore, decreases in IL-10 and interferon-γ mRNA expression were observed in the ileum. The CD4-presenting lymphocytes were decreased significantly in the ileum and mesenteric lymph node, whereas CD8-presenting lymphocytes were increased in the blood of females (Fleige et al., 2007).
Fermentable substances such as inulin or lactulose have been proposed to stimulate the immune system and health by modulation of the intestinal flora and its fermentation products. In a study, effects of inulin and lactulose on the intestinal health and hematology of calves have been investigated. Only inulin was able to increase hemoglobin concentration and hematocrit mRNA expression of inflammation-related markers in the intestine was also affected by both prebiotics hinting at a decreased inflammatory status. This may be due to a possible decrease in intestinal pathogen load. mRNA expression of interleukin 8 were increased by lactulose in mesenteric lymph nodes. In the ileum, expression of a proliferation marker was increased by inulin while an apoptosis-related gene was increased by both prebiotics (Masanetz et al., 2011). Prebiotics supplementation may influence innate immune responses, such as phagocytosis and oxidative burst, cytokine production, and antibody response may be influenced. Mice supplemented with 10% oligofructose or inulin had increased peritoneal macrophage phagocytosis and macrophage superoxide production compared to control mice (Trushina et al., 2005).
Table 1: Effect of Prebiotics on Calf
|Young calves||MOS @ 4 g/d of Bio-Mos||Stimulate calf starter intake. Presence of Cl. perfringensandE. coli,and Salmonella spp. Decreases.||(Terre et al., 2007)|
@ 5 g/day pre weaning and 10g/day post weaning
Clostridium coccoides–Eubacteriumrectalegroup was higher in the feces
|(Uneyo et al.,2015)|
|Veal calves||Calf milk replacer with and without 3 or 6 g of scFOS||Growth performance
Faecalconc of SCFAs
|(Grand et al.,2013)|
|Calves||mannan oligosaccharide (MOS) mixed in the whole milk @ 4 g of Bio-Mos per calf daily||consumed 19.9% more calf starter
|(Hasunuma et al.,2011)|
|Young calves||MOS @ 4 g/d of Bio-Mos||Stimulated calf starter intake. Presence of Cl. Perfringens and E.coli, and Salmonella spp. and Cryptosporidium spp. not effected effect||(Terre et al., 2007)|
|Calves||MOS in milk replacer @ 2-4 g/day/head||Prevents the bacteria from attaching to intestinal epithelial cells||(Karol et al., 2011)|
|Calves||MOS milk replacer @ 4g /day/head||Better growth performance
Feed cost/kg B wt gain
|(Ghosh et al., 2011)|
|Neonatal calves||Prebio-Support@ 20g/day||Enhance the immune system by evoking a direct antibody response||(Heinrichs et al.,2011)|
|Calves||Prebio Support containing DHNA||Bifidobacter population
Fecal water , fecal ammonia and S
SCFAs Fecal Consistency better
|(Fujisawa et al.,2009)|
Macrophage phagocytosis was also increased when calves were supplemented with β 1,4mannobiose compared to control calves (Ibuki et al., 2010). An in vitro study in humans found an increase in neutrophil oxidative burst response and microbicidal activity with beta glucan supplementation (Wakshull et al., 1999). Peritoneal neutrophil respiratory burst activity and neutrophil number were also increased in mice supplemented with oat beta glucan (Murphy et al., 2007).
The fermentation products produced by prebiotics such as butyrate (Nilsson et al., 2010), may indirectly effect anti-inflammatory cytokines. Butyrate is one of the most prevalent fermentation products in the rumen and has been shown to increase the production of anti-inflammatory cytokines (Schley and Field, 2002). Secretion of anti-inflammatory IL-10 was increased in elderly humans supplemented with galactooligosaccharides (Vulevic et al., 2008).Fructooligosaccharide-supplemented rats had increased TGF-β in cecal tissue compared with control rats as well as an increase in commensal microflora counts, Lactobacilli and Bifidobacteria (Hoentjen et al., 2005).
Antibody production of IgA which plays a role in mucosal immunity and IgG, important in memory responses, may also be influenced by prebiotics. Ileal IgA concentrations from dogs supplemented with both mannan oligosaccharides and fructooligosaccharides were increased compared with control animals in a study done by Swanson et al., 2002. Secretion of IgA in peyer’s patch cells of fructooligosaccharide-supplemented mice with was increased in a dose-dependent manner compared with controls (Hosono et al., 2003). Hydrolyzed yeast-fed neonatal calves challenged with both Hog cholera, a viral pathogen, and Erysipelothrixinsidiossa, a bacterium, had increased bacterial- and viral-specific IgA and IgG concentrations compared with challenged calves without supplementation (Kim et al., 2011). Increases in total IgG have also been observed. Beta glucan supplementation increased total IgG concentrations of immunosuppressed mice (Yun et al., 1997). Serum IgG concentrations were improved by 32% and 23% compared to controls in two trials involving mannan oligosaccharide-supplemented piglets (Lazarevic et al., 2010). In a third trial by the same researcher, Holstein calves fed mannan oligosaccharides had an increase in serum IgG concentrations of 39% (Lazarevic et al., 2010).
Dietary supplementation of prebiotics is a valuable approach in improving gut health attributes like bifidogenecity, hindgut fermentation, gut mucosal integrity, mineral bioavailability, lipid and glucose homeostasis and immune response. They have added benefits in terms of easy accessibility, easier integration into feeding system and exploitation of non-viable dietary components. Moreover, they can be fortified in wide range of feeds. However, to obtain optimal results, standardization concerning specific choice of prebiotic, dietary inclusion level, adaptation period, chemical structure (degree of polymerization, linear or branched, type of linkages between monometric sugars), origin of prebiotic, route of administration, animal factor (species, age, stage of production and health status) and proper managemental care is required. In this perspective it would be possible to compare data from different experiments and to provide the basis for more refined clinical trials. Future research required focusing on determining the mechanism of action, evaluating prebiotic interaction and elucidating how the genetic and bacterial profiles of the host can influence treatment responsiveness. Moreover, as better information on structure to function information accrues as well as individual metabolic profiles of target bacteria are compiled, it may be easier to select prebiotics for specific purpose. With the new generation of molecular microbiological tools now becoming available, it will be possible to gain definitive information on the species rather than genera that are influenced by the test prebiotic. The more we identify and characterize the bacterial genera, species and even strains that compose the intestinal microbiota, the more we can understand both qualitatively and quantitatively, changes in that composition, their physiological roles and mechanisms of effects. Good management practices to optimize nutrition, immune status, and decrease the risk of disease are vital. The use of prebiotics may be a viable option to increase the proliferation of commensal bacteria in the gastrointestinal tract, modulate feeding behavior, and increase immune function to optimize calf health.