by-DR. Prashant Yogi, Veterinary Ayurveda Livestock Consultant,Satara,MH.
Aloe vera, as an additive to livestock and poultry feed, has great potentials for improving nutrient utilization, intestinal health, immune response and growth performance. It has potential benefits as antimicrobial agents and used for controlling coccidiosis in poultry. Advantages of aloe vera added to feeds depend on several factors like form of use [powder, gel, extract (ethanolic or aqueous), polysaccharide extracted from gel], dosage, genetics of animals, ingredients of diet and farm management.
Recently the ban on the use of antibiotic as a growth promoters (AGP) in animal feeds, due to their residual effect in animal products as well as development of bacterial resistance in animals and human body, have make a way to look for alternatives of antibiotics in order to eliminate their impact on animals . Many feed additives like prebiotics, probiotics, organic acids and plant extracts have beneficial effects on animal production. Medicinal herbs properties to improve digestibility, antimicrobial, anti-inflammatory, antioxidant and immune-stimulant activity must be exploited in feeding of animals as well as safe food product for human beings. Now a day’s aloe vera popularly used by naturopaths, yoga gurus, alternative medicine promoters and feed additives. Given the significance of healthy animal food as well as human health, a broader range of research is dedicated to replace antibiotic growth promoter (AGP) with other additives, especially probiotics, prebiotics, enzymes, organic acids, and herbs .Many studies have been carried out on using additives, including medicinal herbs, as alternatives to antibiotics, with direct or indirect effects on animal growth and performance. Medicinal herbs, as a new class of additives to animal and poultry feeds have beneficial properties such as antioxidant, antimicrobial, and antifungal as well as immunomodulatory and anticoccidial effects, which lead to increased use of herbs. Furthermore, many countries around the world, with plenty resources of different kinds of medicinal herbs, can use these herbs as natural feed additives for animals and poultry. The main emphasis is on those herbs that are used to supplement feeds, are helpful in achieving a larger number of objectives (improving nutrient utilization and growth performance, immunity response, intestinal microflora, and controlling particular diseases); in other words the focus is on multifunctional herbs. The most important part of aloe vera is leaf which is composed of two main sections: latex and gel .The gel is composed of about 98.5-99.5% water and the remaining dry matter contains more than 75 biologically active ingredients which have medicinal effects that are useful in treating diseases. Major ingredients of aloe vera include anthraquinones, polysaccharides, vitamins, enzymes and low molecular weight compounds which gives aloe vera its antiinflammatory, immunomodulatory, wound healing, antiviral, antifungal, antitumor, antidiabetic and antioxidant effects. Number of studies have suggest that many benefits of aloe vera are due to its polysaccharides contained in gel, which compose a large part of dry matter in this gel .Almost 60% of dry matter of aloe vera gel is composed of polysaccharides and active compound is acemannan which has immunomodulatory, antimicrobial, and antitumour effects antioxidants, wound healing, immune-modulatory and antidiabetic activites
Aloe vera (Aloe barbadensis miller)———
Aloe vera has a long history of use as a topical and oral therapeutic. It is an acaulescent, perennial plant, and belongs to Xanthorrhoeaceae family. Aloe vera is a native plant of the Mediterranean region but is found all over the world. The Aloe vera leaf can be divided into two main fractions: the green skin, which is rich in 1,8-dihydroxyanthraquinone derivatives and their glycosides, and the colourless pulp that is richer in complex carbohydrates. Mucilaginous jelly like parenchyma is referred to as Aloe vera pulp or gel. This gel has a large content of water (95-99%), and contains proteins, lipids, amino acids, vitamins, enzymes, inorganic compounds, and small organic compounds in addition to carbohydrates. Acemannan (acetylated gluconmanan), also known as carrysin, is the best known among the polysaccharides found in Aloe vera gel. Aloe vera is a source of essential micronutrients and active phyto-chemicals such as ascorbic acid, tocopherols and phenolic compounds which are able to reduce the free radicals that cause reactions of oxidation associated with CVD, carcinogenesis and aging. Many biological activities, including antimicrobial, laxative, protection against radiation, antioxidant, antiinflammatory, anti-tumour, anti-diabetic, antiallergic, as well as hypoglycaemic, gastroprotective, immunomodulatory and wound healing effects, have been attributed to this plant gel.
2. Chemistry of Aloe Vera ——-
The chemistry of aloe vera is quite complex and it has more than 200 different types of bioactive molecules which is responsible for its medicinal and growth promoting properties. The aloe vera leaf gel contains about 98% water whereas, total solid content of aloe vera gel is 0.66% and soluble solids are 0.56%. On DM basis aloe gel consists of polysaccharides (55%), sugars (17%), minerals (16%), proteins (7%), lipids (4%) and phenolic compounds (1%). The gel also contains number of vitamins including the important antioxidant, vitamins A, C and E. Vitamin B1 (thiamine), niacin, Vitamin B2 (riboflavin), choline and folic acid .Also contains many minerals like calcium (involved in teeth and bone formation, muscle contractions and heart health), magnesium (provides strength to teeth and bones, maintains healthy muscles and nervous system, activates enzymes), zinc (speeds up wound healing, mental quickness assists with healthy teeth, bones, skin, immune system, and digestive aid), manganese (activates enzymes, builds healthy bones, nerves and tissues), chromium (assists with protein metabolism and balancing of blood sugars), selenium which all influence our brain performance. Additional minerals found in aloe vera include copper, iron, potassium, phosphorus and sodium, aloe vera also contains the trace minerals of rhodium and iridium used in cancer and tumor research experiments. Many of the medicinal effects of aloe leaf extracts have been attributed to the polysaccharides found in the inner leaf parenchymatous tissues but it is believed that these biological activities should be assigned to a synergistic action of the compounds contained therein rather than a single chemical substance.
Biological activities of aloe vera in livestock and poultry
3.1 Effects of aloe vera supplementation on growth performance
Higher body weight gain, better feed conversion efficiency (FCE) and production of milk, meat and eggs are important economic goals in livestock and poultry farming. Earlier these goals are achieved by feed additive like antibiotics, but ban on application of antibiotic growth promoter (AGP) have affected these goals, resulting in poor growth performance and production of animals. Many researchers have done to examine potential effects of feed additives, like prebiotics, probiotics, organic acids and herbs, on growth performance and production compared to those of antibiotics. An experiment conducted by khan et al. on birds fed diet supplemented with 1 % or 2 % aloe vera leaves had greater body weight gain, better feed intake and FCR than those fed diets without aloe vera leaves. An experiment comparing the effects of aloe vera gel (mixed with feed) and AGP (virginiamycin) indicated that AGP resulted in better growth performance compared to the performance of groups that received aloe vera gel (at 1.5%, 2% and 2.5%), and the control group while no significant difference was observed between the antibiotic group and the 2% aloe vera gel group in terms of body weight gain and FCR .These results are agreed with findings of Mehala and Moorthy. Similar to this finding, Mmereole also observed that at 1 % dietary inclusion of aloe vera leaves powder in broiler diet, there was significant difference in body weight gains in birds fed aloe vera supplemented feed as compared to control group. However, Odo et al. reported that, higher weight gain in birds fed 5 % level of inclusion aloe vera than those of 10 % and explained that aloe vera in large quantitative exerts a powerful purgative effect but in smaller quantity. In an another study, Alemi et al. reported a better growth performance in broilers treated with 0.75% and 1% aloe vera gel powder compared to the 0.5% aloe vera gel powder group and the control group. In support of this, Danhoff and McAnally observed that the feeding of aloe vera accelerated the growth of new cells, thereby resulting to increase body weight. Contrary to above studies, Hassanbeigy Lakeh et al. have observed that the supplementation of aloe vera gel (0.6, 1.2, 1.8, 2.4 and 3 m/L) in broiler drinking water had no effect on feed intake over the total experiment period however, higher body weight gain and the smallest FCR was observed in the 1.8 m/L aloe vera gel group. Das et alstated that the addition of 10 ml aqueous extract of aloe gel per litre of drinking water in broiler have beneficial effect on body weight gain and feed conversion efficiency that could be due to diversified antimicrobial activity of aloe vera gel. Actually, polysaccharides of aloe vera (mainly, acemannan) has prebiotic like effect which increase the number of lactobacillus colonies and reduce gram negative bacteria. The fermentation product of lactobacillus is short chain fatty acid that will reduce the pH of lower intestine and create favorable environment for gram negative bacteria. Olupona et al. have also observed that supplementation of aloe vera in drinking water had beneficial effect on final body weight, weekly body weight gain, and average feed intake. There are limited studies on aloe vera as herbal feed additives in pigs. However, in an experiment Qiao et al. found that the 0.05 % aloe vera polysaccharide (AVP) shown better effect on growth of weaned piglets than 0.02 % AVP. They also found that, supplementation with higher concentrations of AVP not only increased ADG, but decreased the incidence of diarrhoea and weaning stress as well.
3.2. Anti-coccidial activity
Coccidiosis is one of the dreaded diseases in poultry that affects mainly intestine that leads to impairs feed utilization, decreases broilers growth and egg production of laying hens and causes death of birds Lillehoj et al. .Generally, Eimeria (E.) species responsible for coccidiosis in chickens include E. tenella, E. necatrix, E. acervulina, E. maxima, E. brunetti and E. mitis . These species infect epithelial cells of the bird’s intestine causing enteritis, bloody diarrhea and immune-suppression in chickens that paves the way to secondary disease conditions. Therefore, poultry disease management and maintenance of the immune functions for maximum consistent production
performance and growth in poultry industry are fundamental requirements for profitable farming. An excellent way to meet these requirements is to use anticoccidial drugs, chemotherapeutic and biological agents including vaccines. Nevertheless, development of resistant pathogenic strains and drug residues in animal products used by the human beings are the major constraints in this regard .The increasing resistance to avian coccidiosis to anticoccidial drugs currently used by the poultry industry together with the requirement for drug and antibiotic free production systems has meant that it is now important to look for new ways to control the diseases. In this regard, aloe vera has been shown to have diverse biological activities. It has been used therapeutically for centuries and is of particular interest due to its historic reputation as a curative agent and dietary supplement .In an experiment Akhtar et al. observed that the orally administration of aloe vera extract (ethanol and aqous extract) in the broiler chicken has significantly lowered the oocyst count in faeces with compared to control group. They also found that the broilers that received aqueous extract of aloe vera pulp had the lowest mean score lesion in caeca and intestine in comparison to the control group and the group that received ethanol extract of aloe vera pulp. Similar to this, Mwale et al. also found that the increase in aloe vera and aloe spicata content significantly decreases coccidian oocyst count. A comparative study has done by Gadzirayi et al. and reported that the anticoccidial effects of A. excelsa were comparable with sulphachlopyrazine sodium monohydrate in terms of improved live weight gains and reducing oocyst output in broiler chickens. Aloe vera treatments show tonic effects on the intestinal tract by benefiting microflora and reducing bowel putrefaction as well as reducing inflammation .In an in vitro trial done by Marizvikuru et al. to know the effect of three concentrations (15%, 30% and 45%) of Aloe vera (L) and A. spicata on the inhibition of the sporulation of avian coccidiaoocysts. Both aloe extracts showed a concentration dependant anticoccidial effect though, A. spicata inhibited sporulation to a greater extent than aloe vera. Similar to this, Yim et al. have also found that dietary supplementation of A. vera resulted in significantly lower gut lesion scores and reduced faecal oocyst shedding of E. maxima in broiler chickens. They also suggested that reduced faecal oocyst shedding; a protective role against eimeria infection in aloe-based chicken diets could be associated more with cell-mediated responses than antibody responses.
3.3. Antimethanogenic effect
Rumen is a diverse and unique microbial ecosystem composed of bacteria, protozoa, fungi and bacteriophage. In rumen hydrogen is produced during the anaerobic fermentation of nutrients. This hydrogen can be used during the synthesis of volatile fatty acids (VFAs) and microbial protein synthesis. The excess hydrogen from NADH is eliminated primarily by the formation of methane produced by methanogens. Methane is one of the greenhouse gasses which have 21 times more global warming potential than carbon dioxide. Methane produced in ruminants represents a substantial loss of 7-9% of gross energy intake which reduces the potential conversion of feed energy to metabolizable energy. Hence, the inhibition of methanogenesis has long been considered from nutritional aspects and more recently from the perspectives on greenhouse gas emissions. It is a challenging task for the animal nutritionist and rumen microbiologist to make livestock industry economical and eco-friendly by controlling heat production and methane emissions from the ruminants. To combat this problem, many attempts like concentrate supplementation, use of lipid supplementation (Nevel and Demeyer, antibiotic growth promoters such as monensin and lasalocid, different categories of feed additives like halogenated methane analogues, bacteriocins, propionate enhancers, acetogens, fats, ionophores, defaunating agents, formate etc. had been tried, but the goal could not be successfully achieved either due to some harmful effects on animal itself or due to the presence of their residues in the animal products. Contrary to this, plants containing secondary metabolites are being used in the ethno-veterinary medical practices since long back and have yielded good effects on the animal health. One of the most promising known therapeutic plants is surely aloe. The middle part of leaves containing gel, made up of carbohydrates (acemannan), anthraquinones, enzymes, inorganic compounds, amino acids, vitamins and a miscellaneous (including salicylic acid). These potentially active chemical constituents give aloe well known therapeutic properties like wound healing, antiinflammatory, immune-stimulating etc. Calabro et al. observed that a significant effect of Aloe arborescence supplementation on the in vitro fermentation characteristics of feedstuffs. The supplementation of 120 mg aloe higher than that advised for in vivo, has beneficial effect on gas production compared to the lowest dosage. The close association between SCFA and gas production in vitro is an indicator of energy availability to the animal .Hence, the increased volatile fatty acids production due to the aloe supplementation probably means higher milk yield and quality, especially in terms of fat. A. arborescens has interesting effect on the rumen microbial in vitro activity, stimulating microbial metabolism thereby increasing the volatile fatty acids production in the rumen. These effects may be attributed to the plant extracts rich in some active chemical compounds (flavonoid) that increase degradation of cell wall constituents, yield and efficiency of microbial protein synthesis (Sirohi et al., Similar to this, Sachan et al had supplement five herbs namely Trigonella foenum-graecum (Methi), Acacia concina (Shikakai), Trachyspermum ammi (Ajwain), Cinnamomum tamala (Tejpatta) and Aloe barbadanis (Aloe vera ) at the rate of 1.5%, 2.5% and 4.0% of ration and found that the addition of these herbs had no any adverse effect on rumen pH. There was significant (P< 0.05) improvement in IVDMD and IVOMD (%) of feed after addition of Trigonella foenum-graecum (66.22, 69.63) as compared to control (56.33, 61.37) respectively. Similarly, addition of aloe vera also tended to improve the IVDMD and IVOMD of feed in respect to control. Addition of other herbs Acacia concina (Shikakai), Trachyspermum ammi (Ajwain), Cinnamomum tamala (Tejpatta) did not show any improvement in the feed digestibility. Authours, concluded that Trigonella foenum-graecum, and Aloe barbadanis are the potential fermentation modifier. In agreement of this, Sirohi et al. also reported that among the different extracts tested, IVDMD (%) increased by 15.42% after addition of Aloe-barbadanis.
3.4. Antifungal activity
There are many studies showing that resistance to infections enhanced by aloe either in animals, whether the infective agent is a bacterium, virus or fungus. The aloe extract showed the significant antifungal activity against numbers of fungi like, Aspergillus niger, Crytococcus neoformans, Penicillium maneffei, F. oxysporum, Phythium sp. and R. solani. Candidiasis infections are mainly caused by Candida (fungus) in a variety of places like a soral (thrush), vaginal and gastrointestinal tract. These are normally treated with the help of antifungal drugs, but aloe vera can remove candidiasis infections with its natural antifungal properties. Aloe vera shows its antifungal activities against other fungi such as Candida paraprilosis, Candida krusei and Candida albicans Saks and Golan reported that, the gel extract from leaves of aloe vera possesses inhibitory action on spore germination and mycelial growth of four common post harvest fungi, P. digitatum, A. altemata, B. cinerea, and P. expansum. The present study is in agreement with Fujita et al. in which they confirmed the antifungal properties of aloe species, Aloe arborescens Miller spp. Natulensis Berger, active against the human fungal pathogen Ttichophyton mentugrophytes.
3.5. Antiparasitic activity
Endo and ecto-parasites are very common in domestic animals especially in grazing animals, and they cause large economic losses. Alagesan et al. made comparison between the following four sets of ingestible i.e albendazole, neem oil, extract of neem seed with bittergourd, garlic, edible banana stem and aloe vera and reported that the aloe vera has strong antiparasitic activity. Similar to this,] have also observed the beneficial effect of Aloe variegata, spread over mange lesions.
3.6. Effects on intestinal microflora——-
Maintenance of intestinal microflora is an important factor contributing to improved growth performance and immune response in animals. Extract of herbs play a significant role in balancing and improving intestinal microflora in animals. Pogribna et al. reported that dietary supplement of aloe vera, may alter the production of short chain fatty acids and number of intestinal microflora. Many studies have been carried out on using additives, including herbs, as alternatives to antibiotics, with direct or indirect effects on intestinal microflora. Many studies have shown antimicrobial properties of herb extracts., which can improve intestinal microflora population and enhance health of digestive systems through reduction in number of disease making bacteria. Number of studies have reported antibacterial effects of Aloe veragel . These studies, indicates that aloe vera supplementation in broilers’ have beneficial effect on improving intestinal microflora, its ecosystem and gut morphology; increase in aloe vera gel in broiler feeds (1.5%, 2%, and 2.5%) leads to increased Lactobacillus count and decreased E. coli count .In addition, Jiang et al. also have reported an increase in Lactobacillus and Bifidobacteria count as well as a reduction in E. coli when acemannan (0.1% and 0.05%), polysaccharide (0.1%) and aloe vera gel (0.1%) were added to broiler feed. In another study, Dai et al. found that herbs and polysaccharide contained in aloe vera can reduce E. coli count while increasing the number of Lactobacillus and Bifidobacteria. Although the exact mechanism by which aloe vera affects intestinal microflora in broilers is unknown, it is likely that this effect is similar to the antibacterial effects of some herbs, or likely that the polysaccharide contained in aloe vera (acemannan) has mechanism like that of prebiotics (Guo et al., .where as some researchers believed that the antibacterial effects of aloe vera to its fumaric acid content.
3.7. Antioxidant effect
Reactive oxygen species (ROS) is continuously produced during normal physiological events and they can easily initiate the per-oxidation of membrane lipids, leading to the accumulation of lipid peroxides. Under pathological conditions, ROS is overproduced and results in oxidative stress. Antioxidants are substances that delay or prevent the oxidation of cellular oxidizable substrates. They exert their effect by scavenging reactive oxygen species, activating a battery of detoxifying proteins or preventing the generation of reactive oxygen species (Halliwell et al.. In recent years, there has been an increasing trend in finding natural antioxidants, which can protect the body from free radicals and retard the progress of many chronic diseases (Kaur et al., Patel et al. observed that both the plants (somnifera and aloe vera) possess excellent antioxidant and free radical scavenging activity. Screening of both the plant at different doses (100, 150 and 200 µg/ml) help to reveal the potential of individual plants. Both the plant possess almost equivalent hydrogen peroxide scavenging activity while the total antioxidant capacity was found much better in Withania somnifera as compare to aloe vera. The antioxidant activity of both the plant might be attributed to its polyphenolic content and other phytochemicals constituents.
3.8. Hypocholesterolemic effect
High blood cholesterol is a major risk factor for heart disease and stroke in human being. Daily supplementation with aloe vera stimulates immune system and improves wound healing. Iji et al. has divided 40 male wistar rats into four groups of ten rats per group. Group I which served as the control received 0.9% physiological saline while those in groups II, III and IV received aloe vera gel (100, 250 and 500 mg/kg) respectively, for four weeks. There was significant decrease in serum cholesterol levels.
3.9. Immunostimulation/Immunosuppression
The immunomodulating effects of aloe-based carbohydrates are thought to function via activation of macrophage cells and stimulation of the antigen processing. Activated macrophage cells generate NO, secrete cytokines such as TNF-α and IL-6 and present cell surface markers. In a study, aqueous and
ethanolic extracts from the aloe vera pulp exerted stimulatory effects on humoral and cellular immune responses in chickens. The higher cellular immune responses in aloe vera administered chickens may be due to the aloe polysaccharides, especially acemannan (ACM), which activated the macrophages to produce inflammatory cytokines such as IL-1, IL-6 and TNF .The ability of aloe vera to stimulate the immune system is attributed to polysaccharides present in the aloe vera gel . Acemannan was found to have immunomodulatory activity. It activates macrophages, enhance cytokine release, stimulate interactions between macrophages, T-lymphocytes and B-lymphocytes and enhance the generation of cytotoxic T-lymphocytes. An important property of aloe vera that has been the subject of many in vivo and in vitro experiments is improvement in immune response, probably due to the acemannan contained in aloe vera, .Acemannan is a β (1-4)-linked acetylated mannan having mannose that can attach to mannose receptors in macrophages (Karaca et al., .and activate these macrophages. Acemannan is potentiating antibody production against coxsackie virus and reduce radiation induced skin reactions in C3H mice. Acemannan is also responsible for enhancing the alloresponsiveness of human lymphocytes as well as induced the phenotypic and functional maturation of immature dendrite cells 60 and also stimulate the phagocytosis and the candidicidal activity of macrophages (Lee et al., Alprogen inhibit calcium influx into mast cells, thereby inhibiting the antigen-antibody-mediated release of histamine and leukotriene from mast cells. Ro et al. in a study on mice that had previously been implanted with murine sarcoma cells, acemannan stimulates the synthesis and release of interleukin-1 (IL-1) and tumor necrosis factor from macrophages in mice, which in turn initiated an immune attack that resulted in necrosis and regression of the cancerous cells. In an experiment on aloe vera effects on immunity of broilers, Valle-Paraso et al. reported that, broilers treated with 2% aloe vera gel (with their drinking water) showed significant increase in antibody titer against newcastle disease virus (NDV) on days 37 and 52, compared to the control groups. Similar to this study Darabighane et al. also reported an increase in antibody titer against NDV on days 24 and 38 by adding aloe vera gel to broiler feeds (at 1.5, 2 and 2.5%). In another study, Alemi et al. added aloe vera gel powder (at 0.5, 0.75 and 1%) to broiler feeds and reported an increase in antibody titer against NDV.
3.10. Effects on reproductive performance
Estakhr and Javdan, was carried an experiment to access the effect of aloe vera on reproduction, for that he administered aloe vera leaf pulp extract, gel extract and a mixture of both to three groups of 10 week old male wistar rats for 56 consecutive days and found that in all groups except control group the weights of the testes have increased. Epididymal sperm counts and sperm motility have been significantly increased compared to control groups. The testosterone level has remarkably increased in treated groups. As per these results, aloe vera has strong spermatogenic activity by increasing sperm parameters. This study strongly proposes that aloe vera specially its gel fortifies spermatogenesis and can be a good candidate for manufacturing fertility drugs. Contrary to this study,
Oyewopo et al. suggest that aloe vera has potential antifertility effects in the male rat.
3.11. Antitumor Effects
Polysaccharides isolated from aloe vera have been reported to have antitumor activity and the antitumor activity of acemannan has been examined in several animal species. A modified aloe vera polysaccharide, G2E1DS2 isolated from cellulose treated aloe vera gel was shown to activate macrophages and exhibit potent antitumor activity when injected into the peritoneum of mice implanted with sarcoma cells Similarly, intra peritoneal administration of both enriched and commercial forms acemannan to mice implanted with murine sarcoma cells significantly reduced the tumor burden and increased the survival rate .Supplementation of the cancer induced rats with vitamin C or aloe vera gel extract significantly inhibited the development and severity of carcinogenesis as reflected in the reduction of the percentage surface area of enzyme positive foci .
3.12. Adverse or Toxic
Effects Consumption of aloe vera latex is also associated with watery diarrhoea leading to electrolyte imbalance and hypokalemia .Other side effects include weight loss, central nervous system disturbances and abnormalities and kidney dysfunction. Compounds in aloe vera latex are also considered genotoxic and may be mutagenic .The abuse of aloe vera latex containing laxatives is associated with melanosis coli, which may play a role in the development of colorectal cancer. Intestinal tumours were induced in rats that consumed a diet containing chrysazin, a synthetic anthraquinone with dihydroxy groups like other natural anthraquinones. In addition, compounds in aloe vera latex are suspected to interact with certain oral conventional drugs in particular corticosteroids and cardiac glycosides .
Reference:On request.
