PLEUROTUS TUBER-REGIUM IN ANIMAL PRODUCTION
By Ifeanyi Charles Okoli
Publish Date: 4th April 2023
Introduction
The food and fiber extraction activities especially in agricultural production generate a lot of biomass waste in different regions of the world. Most of the large volumes of agricultural by-products or residues produced by farmers in tropical countries are discarded as waste because the farmers lack the needed technological information on how to convert them into useful products. Some of these by-products are exploited in their raw form as feedstuff by livestock farmers and have been shown to have low feeding value because of their fibrous nature. Several processing approaches such as mechanical treatments (size reduction, soaking, heating), chemical treatments (alkali, sulfide, acid, solvent extraction), and biological treatments (enzyme, fermentation) have been used to improve the feeding value of these fibrous materials for different livestock species with some success. Some methods are more suitable for specific livestock species based on their feeding habits and nutrient requirements. Bio-degradation of fibrous feedstuff using solid-state fermentation has particularly been found applicable not only to feedstuffs targeted for use in ruminant nutrition because of its ability to break down and release nutrients bound in the feedstuff but also to produce bioactive substances such as enzymes that aid feed digestion in monogastric animals. White rot fungi such as mushrooms employed in solid-state fermentation also contain bioactive substances that have been shown to have both nutritional and pharmaceutical benefits in animal production.
Mushrooms grow on different types of biomass substrates on which they serve as primary decomposers and can degrade many components of plant material, including cellulose, hemicellulose, lignin, and proteins. Several reports have shown that different species of mushrooms play useful roles in animal production. For example, they act as valuable sources of nutrients and bioactive substances such as polysaccharides, proteins, essential amino acids, fiber, unsaturated fatty acids, phenolic compounds, tocopherols, and carotenoids, which have been linked to improved gut health, physiological and performance status of animals. The ban on in-feed antibiotic growth promoters in many countries has elicited research into the use of mushrooms as safe alternative growth promoters. The mushroom hyphae secrete large amounts of enzymes such as cellulase, lipase, amylase carboxymethyl cellulase, proteinase, and peroxidase which are responsible for the degradation of lignocellulosic materials and proteins in the substrates and have been exploited in animal nutrition. The use of mushrooms in biomass degradation could be adopted by farmers as a simple technology for converting the abundant biomass wastes to value-added cheap feed materials while producing high-quality food and feed additives.
Nutraceutical value of P. tuber-regium in Animal Production
According to Astudillo-Neira and co-workers, Pleurotus mushrooms exert beneficial effects on nutrition and health through their bioactive compounds such as polysaccharides, β-glucans, proteins/enzymes, peptides, lectins, terpenoids, polyketides, and phenolic compounds which are increasingly being applied in drug formulations and human diet. Their fruiting body and mycelial biomass have a range of characteristic aromas and flavors attributed to carbohydrates, lactones, amino acids, and terpenes and have been exploited in the improvement of flavor and palatability in foods. The rich protein and essential amino acid contents have enabled their use as substitutes for meat, while the chitin-rich cell wall has been used as a source of dietary fiber, vitamins, micro and macro-elements, and carbohydrate in diets. The low fat and almost zero cholesterol content the mushrooms have also been exploited in the formulation of specialized diets. Concerning their chemical constituents such as secondary metabolites, betalains, alkaloids, glycoproteins, and polysaccharides, the Pleurotus genus remains one of the most diverse edible and medicinal mushrooms.
For example, the fruit body and sclerotium of P. tuber-regium have specifically been shown to exhibit hematinic, immuno-stimulant, anticancer, anti-inflammatory, antimicrobial, hypolipidemic, hepatoprotective, and antihyperglycemic properties which could be exploited in different ways in animal production. Its ability to promote the growth of beneficial bacteria, inhibit the proliferation of harmful microbes, enhance immunity, and stimulate the growth and proliferation of the absorptive cells in the gut has also been reported by Sethiya, and several other researchers. These nutraceutical and growth-promoting properties have been attributed to their phytochemical constituents, especially the significant amounts of non-starch polysaccharides (e.g. β-glucan) found in its cell wall and are currently being exploited in various ways in animal production.
Improvement of Nutrient Values of Feedstuff
Most traditionally available ruminant forages are characterized by low carbohydrate and high lignocellulose content, which is converted to valuable nutrients such as short-chain fatty acids, especially acetic, propionic, and butyric acids through the actions of microflora in the gastrointestinal tract of the ruminant animals. The production of these acids has been correlated to the forage content of cellulose, hemicellulose, lignin, starch, and sugars, among other nutrients. A major constraint to ruminant production in many parts of the world is the seasonal fluctuation in both forage quality and quantity. This has led to numerous studies on the conservation of excess forage for use in periods of scarcity to ensure adequate feeding of livestock. Traditional technologies such as hay and silage making have been used to achieve this and according to Astudillo-Neira and co-workers are usually performed at the beginning of the maturation stage or once maturation has already begun, which implies a decrease in available nutrients and an increase in fiber content. The lignin in the cell wall of most forage materials is usually indigestible for ruminants and their rumen microflora. The lignin also renders other cell wall carbohydrates unavailable to microbial and enzymatic actions in the rumen by linking both hemicellulose and cellulose, thereby forming an impenetrable material. Several research efforts have been made to enhance the degradation of the lignocellulosic complex using different types of fungi.
For example, xylophagous fungi such as edible mushrooms like Pleurotus species are excellent lignin degraders, and according to Janusz and colleagues are the only group of microorganisms able to mineralize and completely degrade lignin to CO2 and H2O. Generally, fungi have two types of extracellular enzymatic systems: the hydrolytic system, which produces hydrolases that are responsible for polysaccharide degradation, and a unique oxidative and extracellular ligninolytic system, which degrades lignin, with the aid of ligninolytic enzymes such as laccases, lignin peroxidase, manganese peroxidase, and multifunctional peroxidase. Figure 1 shows the schematic diagram of lignin degradation by basidiomycetes white-rot fungi.
The Pleurotus mushrooms are important to livestock nutrition on the bases that they are ligninolytic fungi that can colonize a wide variety of lignocellulosic substrates without compromising cellulose and hemicellulose, thus performing a bioconversion that improves the nutritional contribution of these materials when included in ruminant diets, and making them the preferred fungi for improving feed quality. Most studies on the use of Pleurotus species in forage improvement extend their cultivation until the harvest of the fruiting bodies, which implies the depletion of the nutrients in the spent substrates meant for animal feeding. Short fermentation of substrates with Pleurotus mushroom without the formation of a fruiting body, has however been shown to improve the nutritional quality of the fermentation substrates. Fazaeli and co-workers reported that a 21 days fermentation of wheat straw using P. ostreatus resulted in significant decreases in neutral detergent fiber and acid detergent fiber with increased crude protein and in vitro digestibility.
Astudillo-Neira and colleagues evaluated the effect of 14 days of solid-state fermentation of hay derived from ryegrass-fescue with P. ostreatus, on its nutrient quality. At the end of the fermentation period, crude protein increased marginally from 4.73 to 5.16 percent, while non-fibrous carbohydrates increased moderately from 20.84 to 25.04 percent. The neutral detergent fiber however decreased from 68.72 to 64.87 percent and acid detergent lignin from 5.88 to 1.98 percent. Enzymatic activity assays showed that lignin peroxidase and laccase reached higher activity on day 14 (19.51 U/L and 34.17 U/L, respectively), whereas manganese peroxidase displayed stability beyond 14 days. These results indicate that lignocellulosic feed bioconversion by P. ostreatus improves the nutrient value of fibrous feedstuffs during 14 days of solid-state fermentation. Researchers at the University of Ibadan, Nigeria, investigate the potential of P. tuber-regium in the degradation of rattan wood and maize stovers after 30, 60, and 90 days of fermentation. They reported significant increases in crude protein content in degraded rattan wood from 1.60 to 5.90 percent and in maize stovers from 2.75 to 8.74 percent, while crude fiber decreased significantly from 44.68 to 20.92% for rattan wood and 32.33 to 13.03 percent for maize stovers after 90 days of incubation. Ether extract, ash, and dry matter contents also decreased in both substrates, and carbon, nitrogen, and potassium contents increased significantly. There was also a significant reduction in the loss of organic matter from the substrates as the period of incubation increased indicating that such biomass wastes could be processed into nutritive raw material for compounding ruminant feeds.
In another Nigerian study at Nasarawa State University, Lafia, the effects of treatment with three edible Pleurotus mushrooms; P. ostreatus (POR), P. pulmonarius (PPR), and P. tuber-regium (PTR) on the nutritive value of rice straw was studied. The P. tuber-regium caused an increase in the crude protein from 4.69 to 7.69 percent, while the crude fiber value decreased from 32.89 to 19.96 percent. Treatment effects on cellulose, neutral detergent fiber, acid detergent fiber, and acid detergent lignin contents were also significant. The estimated metabolizable energy, organic matter digestibility, and short-chain fatty acid (µm) ranged from 6.47 to 7.54 MJ.kg-1 DM, 51.17 to 57.02 percent, and 0.657 to 0.848 µm for POR. The treatment effect on the insoluble but degradable fraction was significant ranging from 22 to 28.33 mL in the PTR. It was therefore concluded that treatment of rice straw with different edible mushrooms improves the potential feeding value of the resultant substrate for ruminants. Again, working at the University of Ibadan, Jonathan and Akinfemi used the fruiting bodies of the white rot fungi, Lentinus subnudus and P. tuber-regium to degrade maize cobs in a solid-state fermentation experiment that lasted 56 days. Proximate composition and fiber fraction value changes resembled those reported earlier as shown in table 1, with the white rot fungi treatments resulting in significant increases in crude protein, ether extract, ash, nitrogen-free extract values, while dry matter, crude fiber, and metabolizable energy values decreased significantly. Significant increases in values were also obtained in the fungal-treated maize cobs compared with the control for short-chain fatty acid, and organic matter digestibility. The L. subnudus had significantly better degradation effects on the maize cobs as shown by the proximate fiber fraction results.
Table 1: Nutritional compositions of fungal biodegraded maize cob ((g/100g DM)
Figure 5 shows the in vitro gas production pattern from the different treatments. Gas production ranged from 0.16 ml h -1 from the untreated maize cob to 0.20 ml h -1 from the L. subnudus and 0.11 ml h -1 from the P. tuber-regium treated maize cobs. The final volumes of gas produced also differed considerably, with the L. subnudus yielding 15.00 ml h -1, and the P. tuber-regium yielding 19.67ml h -1 while the untreated maize cob yielded 11.67ml h -1, which was significantly lower than the values recorded in the treated cobs.
Effect of P. tuber-regium on Antinutrients
A major constraint to the use of unconventional feedstuff in livestock feeding is their high content of anti-nutritional factors. Examples of the use of cassava and cocoyam as cheap energy sources are limited chiefly by the high content of hydrocyanic acid and oxalates respectively. Rubber seed cake, which is relatively high in protein content is also highly limited because of the long storage period needed for its cyanide level to be reduced to a safe level. According to Ukpebor and colleagues, several methods such as grinding, drying, heat, and chemical treatments as well as fermentation have been used to reduce the level of anti-nutritional factors in unconventional feedstuffs. Wainwright had earlier reported that fungi such as Gloeocercospora sorghi and some species of Gibberella have the ability to convert hydrocyanic acid to a non-toxic formamide.
In a study by researchers at the University of Benin, Benin City, Nigeria, rubber seed cake was treated with the mycelia of P. tuber-regium to assess the effect of its enzymatic activity on the cyanide level and nutritional value of the rubber seed cake. Sterilized rubber seed cake was inoculated with P. tuber-regium spawn at the rate of 3 percent wet weight and incubated for 96 hours. The results showed a 81 percent reduction in the total cyanogen content after 96 hours at room temperature. The cyanide concentration reduced from 500 ppm in the freshly obtained rubber seed cake to 5 ppm for the undefatted rubber seed cake and from 300 to 4 ppm for the defatted rubber seed cake, which is below the 10 ppm limit recommended by FAO/WHO. The proximate analysis of the mycelium colonized substrate showed that protein increased significantly from 29.36 to 39.27 percent further enhancing its use as feed for livestock.
P. tuber-regium in Rodents and Rabbit Production
Researchers at the Michael Okpara University of Agriculture, Umudike, Nigeria studied the effect of dietary incorporation of the sclerotium of P. tuber-regium on the body and organ weights and total triacylglycerols in growing albino mice (Mus musculus). The milled P. tuber-regium was mixed with a standard diet to obtain 5 and 10 percent dietary inclusion and then pelletized and fed to the experimental animals for one week. Dietary incorporation of P. tuber-regium at both levels resulted in a dose-dependent increase in pancreatic weight and a decrease in intestinal weight but had no significant effect on liver and kidney weights. The increase in pancreatic weight was attributed to increased synthesis of pancreatic proteins/enzymes, while the overall result suggests that dietary intake of 5 and 10 percent P. tuber-regium sclerotium has no adverse effects on vital organs such as the liver, intestines, kidneys, and pancreas. Another study carried out at Delta State University, Abraka, Nigeria, investigated the effect of ethanol and aqueous extract of the P. tuber-regium sclerotium on the haematological and serum biochemical parameters in Wistar albino rats. The aqueous extract reduced the low-density lipoprotein (LDL), triglycerides (TG), high-density lipoprotein (HDL), and cholesterol (CHOL) values, in addition to urea, creatinine, Na, K, Cl, and HCO3 ion values in the rats. The ethanol extract, on the other hand, increased the values of LDL, TG, HDL, and CHOL values, while decreasing the creatinine, chloride, and bicarbonate ion values, indicating that P. tuber-regium extracts could be beneficial to the health of albino rats.
Researchers at the National Biotechnology Development Agency, Abuja, Nigeria, investigated the effects of oral administration of aqueous extract of P. tuber-regium sclerotium (0, 500, 750, and 1250 mg/l in drinking water per day) on growth, serum biochemistry, and histomorphology of crossbred growing rabbits during 60 days experimental period. The aqueous extract was prepared by mixing the fine sclerotium powder (> 0.5 mm) with hot water at a ratio of 1:15 w/v. The solution was allowed to cool and then filtered and the filtrate was concentrated and dried in a rotary evaporator at 45°C and stored in air-tight containers at room temperature. The results revealed dose-dependent improvements in live weight, weight gain, feed conversion ratio, water intake, and extract intake. The 750 mg/l level of administration resulted in significant reductions in serum total cholesterol, low-density lipoprotein, very low-density lipoprotein, creatinine, and alkaline phosphatase while increasing the cecal villi height and apical width. There was histological evidence of liver tissue damage at the 1250 mg/l level of administration, indicating that the 750 mg/l administration of the aqueous extract of the sclerotium in drinking water is optimal. In another study on the effect of 0.0, 25.0, 50.0, and 75.0 g/kg dietary inclusion of P. tuber-regium on performance and intestinal morphology of growing rabbits, these researchers reported that weight gain and feed conversion ratio were better in rabbits fed a diet containing 50.0g/kg of the sclerotium powder, while those fed diet containing 75.0 g/kg recorded significantly lower serum cholesterol, creatinine and alanine transaminase, and higher total glucose concentration compared to those receiving other experimental diets. Rabbits fed the 50.0g/kg sclerotium-supplemented diets on the other hand recorded significantly higher caecal apical width than those fed the diet containing zero inclusion. They concluded that supplementation of 50.0 g/kg in the diet enhances the growth performance, cholesterol metabolism, and intestinal morphology of growing rabbits.
P. tuber-regium in Ruminant Production
The nutritional constraint to ruminant production in the tropics is essentially the seasonal inadequacy in the quantity and quality of the feedstuffs. During the long dry season periods in the traditional ruminant livestock-producing zones, farmers try to augment the available poor-quality forage with crop residues, agro-industrial by-products, and forage from evergreen trees. Most of these agro-residues and by-products are highly fibrous, low in digestibility, protein content, and palatability and while the leaves from the evergreen plants may contain high levels of anti-nutrients and therefore requires some form of processing before use. White rot fungi such as Trichoderma and several mushroom species have been researched in recent times for their benefits in improving the nutritive value of locally available fibrous materials for ruminant feeding.
Researchers at the Federal University of Agriculture Makurdi, Nigeria have carried out several investigations into the use of white rot fungi such as P. tuber-regium in the degradation of locally available fibrous feedstuffs for use in ruminant feeding. For example, Wuanor and Carew investigated the nutrient digestibility, carcass yield and production economics of West African dwarf (WAD) goats fed P. tuber-regium biodegraded rice straw and maize offal-brewer yeast slurry mixture. The milled rice straw was mixed with water at a ratio of 1:2 and heaped and then covered with polyethylene sheets to compost for seven days and thereafter opened and allowed to cool. Spores of P. tuber-regium produced by soaking the sclerotium in water for two days were inoculated into the composted rice straw at the rate of one kg of spores to 5 kg of straw on wooden trays and allowed to ferment for 30 days in a relatively humid environment. At the end of the fermentation period, the mass of composted straw now colonized by the mycelium of the fungi showing whitish growths was sun-dried to terminate the growth of the fungi and then used in the feeding trials. Six experimental diets were fed ad libitum containing or not containing P. tuber-regium sclerotium powder as shown in table 2.
Table 2: Experimental diet formulations
Dry matter, organic matter, crude protein, and crude fiber digestibility were highest in the 300 g maize offal-brewer yeast slurry mixture and P. tuber-regium treated rice straw ad libitum at treated rice straw fed group (T6), followed by the 300 g maize offal-brewer yeast slurry mixture and rice straw group (T5). The 200 g maize offal-brewer yeast slurry mixture (T3) and rice straw and 200 g maize offal-brewer yeast slurry mixture and P. tuber-regium treated rice straw (T4) also recorded significantly higher values than the other groups. Carcass characteristics were generally not affected by the feed formulas, while the total revenue results showed a positive response to higher maize offal-brewer yeast slurry mixture and rice straw and P. tuber-regium treated rice straw intakes. Based on these results they concluded that combined feeding of the test materials to the WAD goats enhanced nutrient digestibility, resulted in normal carcass and organ characteristics, and enhanced economic benefits depending on the levels of the test materials fed. In another study at the same institution, Wuanor and Ayoade assessed the growth performance of West African Dwarf goats fed rice straw biodegraded using P. tuber-regium and maize offal mixed with fluid brewers’ yeast slurry in a 1:1 ratio. The experimental animals were fed diets similar in formulation to the ones in table 18. They reported that the P. tuber-regium treatment of rice straw together with maize offal mixed with liquid brewers’ yeast slurry significantly improved the daily feed intake, daily body weight gain, daily water intake, and feed conversion ratio of the animals, thereby portraying the feeding regime as a reliable dry season feed.
At the same Federal University of Agriculture Makurdi, Nigeria, Ochepo and colleagues investigated the effect of P. tuber-regium degraded cassava peels on intake and digestibility by sheep and reported that the inclusion of P. tuber-regium degraded cassava peel meal in the diets tended to enhance feed intake but depressed digestibility beyond 8 percent inclusion level in the diets. In another study, these authors also reported that such diets have no adverse effect on the hematological indices and health status of the experimental animals. A similar study by Jiwuba and colleagues on the effect of P. tuber-regium treated cassava root sievate-based diets on hematology and serum biochemistry of WAD goats also reported that up to 60 percent inclusion had no deleterious effects on the hematological and serum biochemical parameters of goats. Wuanor and co-workers also investigated the nutritive potential of the inclusion of 0, 5, 10, and 15 percent of P. tuber-regium degraded rice offal in the diets of growing Bunaji bulls during a trial period of 90 days. They reported that growth performance indices such as final body weight, daily weight gain, average daily concentrate intake, water intake, and feed conversion ratio improved with an increasing inclusion rate of the P. tuber-regium degraded rice offal in the diets. These studies highlight the potential value of using white rot fungi and P. tuber-regium in particular in exploiting the abundant biomass wastes for improved ruminant feeding.
P. tuber-regium in Monogastric Animal Production
Several commonly used edible and medicinal mushrooms, especially P. ostreatus (oyster mushroom), Agaricus bisporus (Button mushroom), Lentimula edodes (Shiitake mushroom), and Ganoderma lucidum (Reishi mushroom) have been added to diets to evaluate their effects on poultry and pig performance. According to a review by Khan and colleagues, these mushrooms and their polysaccharides can play the following roles in poultry production;
ü The polysaccharides act as immune enhancers and modulators, antibacterial, antiviral, and antiparasitic agents
ü Phenolic extracts act as antioxidants
ü In broiler diets, the mushrooms act as growth promoters
ü In layer diets, the mushrooms improve egg production and quality
ü Mushrooms are used in the induction of molting in old layers
In countries involved in industrial-scale mushroom production, large volumes of mushroom wastes such as oyster mushroom wastes, comprising mainly mushroom stem base and mushroom growth plan rejections have been shown to exhibit antimicrobial, antioxidant, antifungal, and prebiotic properties, and have therefore been used as an alternatives to antibiotic growth promoters in poultry nutrition to enhance performance. Researchers at the Agricultural Research Center, Giza, Egypt, evaluated the impact of 1 and 2 percent inclusions of oyster mushroom wastes in basal diets on the immune responses and the morphology of the intestine of broiler chickens. They reported a substantial increase in body weight gain and feed intake of chickens fed the 1 percent supplemented diet, while the 2 percent supplemented diets recorded similar values as the control, indicating a dose-dependent effect. Song and co-workers also investigated the effects of fermented oyster mushroom (P. ostreatus) by-products at 0, 3, 5, and 7 percent dietary supplementation on growth performance, blood parameters, and meat quality in finishing Berkshire pigs. The results showed that growth performance, blood parameters, carcass traits, and meat quality of the pigs were changed by the addition of the fermented mushroom waste during the finishing days. The addition of up to 3 percent of the mushroom waste produced more significant results than 5 percent. There are currently no published studies on the potential value of P. tuber-regium in poultry and pig performances, indicating the need for such studies.
Pleurotus mushroom mycelial colonized substrate contains many nutrients and bioactive substances and therefore can be used to partially replace standard diets in monogastric animal feeding. Santos and coworkers evaluated the effect of partial replacement of the standard diet with 0, 5, 10,100, and 200 g.kg-1 P. ostreatus colonized substrate on broiler production, health, and meat sensory characteristics. The results showed that at 10 g.kg-1 replacement of the standard diet, the chicken body mass increased up to 57 percent at 21 days and up to 28 percent at 42 days. The mycelial colonized substrate also elicited increased hematocrit, and lymphocyte numbers and reduced low-density lipoprotein values as well as the chicken production period by up to 21 percent without compromising the meat sensory characteristics. Chuang and colleagues also evaluated the effects of waste mushroom compost as a 0, 0.5, 1, or 2 percent feed supplement on the fat metabolism and antioxidant capacity of broilers. They reported that supplementation with mushroom waste compost accelerates adipolysis and enhances the antioxidant capacity of broilers. Among all treatment groups, broilers fed the 0.5 percent mushroom waste compost supplemented diet showed improved feed conversion rate and the highest adipose metabolism. There are however no published studies on the use of P. tuber-regium mycelial colonized substrates or spent substrates in the feeding of poultry or pigs, indicating the need for such studies.
P. tuber-regium in Fish Production
The biological treatment of fibrous materials in the form of solid-state fermentation has been used in animal nutrition and production to reduce their fiber content and improve their nutritive value. Locally abundant biomass residues such as rice husk or hull have been fermented and used in ruminant feeding, while such products have received limited trials in aquaculture production. Researchers at the University of Lagos, Akoka, Nigeria evaluated the effects of P. tuber-regium degraded rice husk, as an energy source on the feed intake, weight gain, feed conversion ratio, hematology, and biochemical parameters in Nile tilapia (Oreochromis niloticus) fingerlings. The dried sclerotium of P. tuber-regium was cut into chumps and soaked in water for 2 - 3 hours and then inoculated into the rice husk, covered with polythene, and allowed to incubate for fifteen days to achieve the biodegradation of the rice husk. The biodegraded rice husk was incorporated into three iso-nitrogenous (35 percent crude protein) test diets at 7.5, 10, and 12.5 percent inclusion levels in partial replacement of maize, and fed to the fingerlings according to standard practice for 70 days. The mean weight gain and specific growth rate were significantly better in the group fed the diet containing the 12.5 percent inclusion of the biodegraded rice hull. Feed conversion ratio however increased with up to 10 percent inclusion level of test ingredients. The addition of the test material reduced the investment cost significantly indicating the overall benefit of the biodegraded rice hull in the production of Nile tilapia.
The researchers also conducted a 70-day feeding trial with Clarias gariepinus (African catfish) juveniles to investigate the effects of partial substitution of soybean meal with sclerotium of P. tuber-regium on growth, nutrient utilization, hematology, carcass proximate composition, and economic parameters. Three experimental diets were formulated with graded levels of sclerotium at 10, 15, and 20 percent inclusion. The poor growth performance was recorded in the fish fed the P. tuber-regium sclerotium supplemented diets coupled with reduced physiological parameters suggesting that it may not favorably replace soybean meal in the diet of C. gariepinus.
Lawal and coworkers in the same institution evaluated the effects of 7.5, 10.0, and 12.5 percent sclerotium inclusion as a substitute for soybean meal in the diet of O. niloticus on growth performance, the economy of production, and hematological and biochemical parameters. The 7.5 percent inclusion level fed group recorded the best weight gain, specific growth rate, and feed conversion ratio, while there was no significant difference in production cost and profit index. They however concluded that up to 12.5 percent inclusion of the sclerotium could be tolerated by O. niloticus.
Conclusion
White rot fungi such as the king tuber mushroom are increasingly being exploited in various aspects of livestock production especially in solid-state fermentation of biomass wastes to improve their feeding values in ruminant production. As a ligninolytic fungus, it colonizes a wide variety of lignocellulosic substrates, thus improving the nutritional contribution of these materials when included in ruminant diets. The bioactive substances contained in both the fruiting bodies and sclerotia such as polysaccharides, proteins, essential amino acids, fiber, unsaturated fatty acids, phenolic compounds, tocopherols, and carotenoids, have also been shown to improve gut health, as well as physiological and performance status of animals.
Supplementation of 50.0 g/kg of sclerotium powder in the diet enhanced the growth performance, cholesterol metabolism, and intestinal morphology of growing rabbits. Similarly, feeding of 200 g maize offal-brewer yeast slurry mixture and rice straw and 200 g maize offal-brewer yeast slurry mixture and P. tuber-regium treated rice straw to WAD goats enhanced nutrient digestibility, resulted in the normal carcass and organ characteristics and enhanced economic benefits depending on the levels of the test materials fed. Again, up to 12.5 percent inclusion of the sclerotium powder in the diet could be tolerated by African catfish, while feeding of the diet containing the 12.5 percent P. tuber-regium degraded rice hull to Nile tilapia resulted in better weight gain, specific growth rate and reduced the investment cost.
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