Cassava wastes as feedstuff 5: Essential additives for cassava waste-based feeds production

Published Date: 6th July 2020

Nutritional considerations

Processed cassava waste products although cheap are usually high in fiber, and like most high fiber feedstuffs, they are relatively poor nutritionally and may contain varying levels of anti-nutritional factors, depending on the processing method. While cassava peel meal and seviates have low crude protein content, the leaf meal is deficient in methionine and other sulfur amino acids. Poorly processed cassava leaf meals may also contain high levels of hydrogen cyanide, in addition to tannin and phytin. Several challenges, therefore, arise when formulating diets with these raw materials. Their high content of insoluble fiber results in low digestibility and high content of undigested material in the digestive tract. This may elicit negative effects on animal health and performance and may encourage the proliferation of pathogens in the digestive tract. Again, the variations in nutrient profiles between sources and even batches, due to differences in cassava varieties, processing and storage methods is a challenge. Sun-dried and finely ground cassava waste products are dusty and may affect feed uptake and digestibility in animals of different ages. Some feed additives are therefore usually added during the production of cassava waste-based diets in order to overcome these shortcomings.

Feed additives are substances or a mixture of substances which are supplemented in animal feeds to improve their quality or enhance the performance of farm animals and the quality of animal products. Their major mains of achieving these are by enhancing the digestive and production efficiency of the animals, thereby lowering the prevalence of pathogens and the impact of livestock on the environment. Some of the feed additives are nutrients and are added in small quantities in feed to provide a balanced nutritious diet. Some act as antioxidants, pelleting and free-flowing agents, anti-molds or help reduce or eliminate anti-nutritional factors, thereby making the feed palatable, digestive, nutritious, and devoid of growth-limiting agents. It is therefore imperative that appropriate additives and essential ingredients should be included in processed cassava waste-based diets in order to produce balanced diets.

Nutrients Supplementation

Proteins: Since cassava peel meal and seviates are low in crude protein and essential amino acids, but moderate in carbohydrate they are mostly included in the diet as cheap energy sources. When using these products as cereal substitutes in poultry feeding, the inclusion of approximately 15 – 20 percent extra protein source is suggested. A recent quantitative score of amino acid profiles of processed cassava products from Nigeria showed that they are poor in all amino acids compared to dried brewers spent grains, palm kernel cake, and groundnut cake. This report indicates that cassava product-based poultry diets should be supplemented with as many amino acids as required at different stages of poultry development, especially the limiting amino acids such as methionine, lysine, and threonine. Specifically, 0.2 to 0.3 percent has been added to high cassava peel meal diets with excellent results in pigs and poultry.

The number of essential amino acids contained in cassava leaf meals are however much higher than those in the peel and seviates and could be as high as those found in hen’s egg when processed as leaf protein, although methionine is limiting. Hydrogen cyanide, high fiber content, tannins, polyphenols, and phytic acids, in the leaf meal, may however limit its bio-availability, nutrient uptake, and digestibility. There is therefore the need to add methionine, phytase, and copper salts in cassava leaf meal-based diets.

Methyl donor: Betaine, a trimethyl derivative found in living organisms that acts as a methyl donor through methionine recycling and as an osmolyte to help maintain cellular water balance, is relatively cheaper than methionine. Betaine was reported to improve the apparent digestibility of lysine, protein, fat, and carotenoids, as well as methionine uptake in broilers challenged with coccidiosis. Betaine could, therefore, serve as an alternative to reduce the inclusion levels of methionine in cassava-based diets, thereby reducing feed production costs. Scientists have reported that broilers fed betaine at 800 mg/kg feed, with sub-optimal supplementation of methionine compared to those fed no betaine, recorded significant improvements in feed efficiency irrespective of the concentrations of other amino acids.

Palm oil and fat: Fat addition has been used to boost the energy content of cassava peel and leaf meal-based diets. Early studies at the Obafemi Awolowo University Ile-Ife, Nigeria, showed that the addition of palm oil to diets containing up to 50% cassava peel meal helped to reduce the toxicity of the diet, through the oil’s ability to delay the decomposition and subsequent absorption of cyanogenic glycosides. They also reported a direct increase in the energy value of the cassava-based diets as a result of palm oil addition. Palm oil has also been used to drastically reduce the dustiness of cassava waste and root-based diets. Research at the University of the South Pacific, Fiji also showed that the addition of tallow to broiler diets in which 45 percent of maize was replaced with cassava peel meal, resulted in improvements in the overall performance of birds over those that did not receive tallow.

Oxidation processes in fat or oil treated feeds and feedstuffs can result in rancidity of fats, destruction of vitamins A, D, and E, carotenoids and amino acids, and also reduce the nutritional value of such feeds. This can lead to nutrient deficiencies and reduced feed intake by animals. Antioxidants such as vitamin E, are therefore included in fat treated diets to arrest food spoilage and rejection by animals.

Common salt: Common salt contains both sodium and chloride and is also called sodium chloride. Salt is a unique additive in animal feeds because animals have a much greater appetite for sodium and chloride in salt than for other minerals. Most plants provide insufficient sodium for animal feeding and may lack adequate chloride content. Therefore, salt supplementation is a critical part of a nutritionally balanced diet for animals. Na+ and Cl- are also critical to the achievement of dietary electrolyte balance that influences feed intake in monogastric animals. Salt can also be used as a delivery mechanism to ensure adequate intake of less palatable nutrients and as a feed intake limiter.

Mineral premix: Minerals fulfill physiological, structural, and regulatory functions in animals. Macro-minerals, such as calcium, phosphorus, potassium, and sodium are needed by animals in significant amounts, while micro-minerals such as zinc, copper, iron, manganese, iodine, cobalt and selenium are only required in trace amounts in the diets. These minerals are usually added in predetermined amounts as commercial mineral premixes in the diets. The thiocyanate produced from the detoxification of cyanide is known to completely inhibit iodine uptake by thyroid glands. Similarly, cyanide exacerbates selenium, zinc, and copper deficiencies in animals consuming poorly processed cassava products. It is, therefore, necessary to make extra allowance for these minerals over and above the normal recommendations when using cassava products in formulating non-ruminant animal diets.

Vitamin premix: Vitamins are also usually delivered in premixes used in the formulation of the diet. Although vitamins are only needed in small quantities in the diet, they are essential, because their impacts on animal performance are enormous. Vitamins serve both as building blocks or energy-yielding compounds and as mediators of the biochemical pathways in the body. Many vitamins are destroyed by oxidation, especially under hot conditions, light, metals such as iron, and certain conditions that may arise due to poor feedstuff storage conditions. Vitamins are divided into fat-soluble (vitamins A, D2, D3, E, and K) and water-soluble (B vitamins and vitamin C). Common techniques used in processing cassava wastes such as heat treatment and direct sun drying may reduce the vitamin content of the final products, so that supplemental additions may be required.

Exogenous enzymes

Exogenous enzymes inclusion in animal diets have been shown to aid feed formulation precision, diet efficiency, and ultimately performance by complementing endogenous enzyme production, thereby enhancing digestion. This is most evident when formulating diets with alternative feedstuffs like cassava wastes. The digestibility of non-starch polysaccharide (NSP)-rich feed ingredients like cassava peels can be improved by treatment with enzymes. Supplementation of NSP degrading enzymes may not only reduce the anti-nutritive effects of NSP but also release some nutrients which could be utilized by the birds. For example, studies on the responses of growing pigs to cassava peel-based diets supplemented with Avizyme® 1300 included at the rate of 0.1% in 45 percent cassava peel-based diet, resulted in enhanced growth as a result of improved protein efficiency and feed conversion.

Enzymes are also combined with other additives to achieve improved utilization of cassava waste-based diets. For example, studies at the University of the South Pacific, Fiji, showed that a combination of tallow and enzyme supplementation improved the utilization of cassava peel meal at 40 percent replacement of dietary maize. Again, a single enzyme may not be enough to target all substrates in a diet, resulting in the need to apply a cocktail of enzymes to effectively breakdown the complex matrixes of fibrous carbohydrates. The negative effects of including 35 percent cassava peel in the diet of growing rabbits were ameliorated in terms of final body weight, and feed conversion ratio by adding a multi-enzyme (cellulase, α-amylase, β-glucanase, phytase, protease, lipase, and xylanase) and high methionine. Similarly, Challenymes, an enzyme cocktail with 8 enzyme activities (β-glucanase, xylanase, β-mannanase, α-galactosidase, amylase, pectinase, protease, and cellulose) is known to improve the degradation of cellulose, and hemicellulose, promote the digestion of starch and protein and improve the efficiency of cassava peel utilization.

In a study conducted at Obafemi Awolowo, University, Ile-Ife Nigeria, cassava plant meal containing unpeeled cassava roots with leaves plus tender-stem mixed in the ratio of 1:2.5 of leaves + tender-stem to unpeeled roots was used to test the combined effects of baker's yeast, hemicell (enzyme), oxytetracycline and palm oil respectively as feed additives in broiler diets. The cassava plant meal had crude protein similar to that of maize (10 percent), while the energy value was 2,857kCa1/kg. The result showed improved nutrient utilization, growth performance, and lowered feeding cost in broilers.

Organic acids

Organic acids are additives used to protect feed from microbial and fungal damage. They serve as preservatives and are also effective in controlling microbial contamination. Organic acids having antimicrobial activities include salts of monocarboxylic acids like furric, acetic, propionic, and butyric acids or carboxylic acids having a hydroxyl group on the alpha carbon, such as lactic, malic and tartaric acids. Similarly, some short-chain carboxylic acids like sorbic and fumeric acids have shown anti-fungal activity. Organic acids inclusion in the diet may be beneficial when the hygiene status of cassava products is not guaranteed due to poor handling and processing, especially when such products are procured from cottage industries that may not have the equipment for efficient drying of the products, thereby exposing them to fungal and bacterial contaminations. Organic acid inclusion in such cases could influence the effects of cassava-based diets in poultry through their ability to alter the enteric ecology of birds towards better feed utilization.

Anti-toxicant additives

The concentrations of hydrogen cyanide in processed cassava products may sometimes not be uniform resulting in some batches having exceptionally dangerous levels. Extra methionine could be added to bind hydrogen cyanide and make the feed safe and also augment the usually low methionine content of cassava-based diets. It has, therefore, become a common practice to include methionine as an anti-cyanide additive in the processed cassava-based diet for poultry. Again, cassava products have high moisture content which makes them vulnerable to mold growth and contamination.

Mold contamination and mycotoxin reduction

Cereals and cassava products when used in livestock diets formulation are subject to mold growth, especially in the humid tropics where the moisture content of the cassava product and finished feeds could be higher than 12 percent during wet periods of the year. Mold contamination can occur in the field or during post-harvest handling, storage, and processing. Mold inhibitors such as organic acids are used to prevent mold growth, but they are not effective against the mycotoxins produced by the molds. Mycotoxins are poisonous chemical compounds produced as secondary metabolites by actively growing molds. There are more than 300 types of mycotoxins that affect animals, but aflatoxin, vomitoxin, zearalenone, ochratoxin, and trichothecenes are the most common. Even when the mold is no longer visible, the mycotoxins remain, and because of this, many modern feed formulations contain mycotoxin binders to bind and prevent mycotoxins from being assimilated into the bloodstream of animals. Commonly branded mycotoxin binders in the market include Mycosorb, Mycofix, and ProSid and Mycoad among others.

Probiotics

Probiotics have been defined as live micro-organisms which when administered in adequate amounts confer health benefits on the host. There is an array of micro-organisms currently being used as probiotics, however, yeast cultures have received a lot of research attention in improving the performance of animals fed high fiber diets. Yeast (Saccharomyces cerevisiae) has been used to influence the microbial populations in the rumen and breakdown of nutrients. Supplementation of probiotics product containing S. cerevisiae and Lactobacillus sporogenes in cassava-groundnut cake meal-based diets fed to starting pigs was found to only enhance mineral metabolism. The addition of direct-fed microbial (live microorganisms, which when administered in adequate amounts confer a health benefit on the host) to weaned pigs diet containing up to 15 kg High-Quality Cassava Peel® as a replacement for 37.5 percent of maize fraction also showed no positive effect on the weaned pig performance.

A Researcher at Anambra State University Igbariam, Nigeria, however, reported that inclusion of up to 50 percent cassava and brewers’ yeast blend at 2.7:1 ratio (9 percent crude protein) completely replace maize in a practical broiler diet with efficiency comparable to that of a maize-soybean meal diet. In another Nigerian study in which oxytetracycline, Avizyme 1500+, and Bakers' Yeast were added to whole cassava plant meal-based diets, the researcher concluded that inclusion of Bakers' Yeast at the rate 3 Kg per ton of cassava-based diets had beneficial effects on fiber utilization and growth rate of the young pig. Brazilian researchers also reported that yeast could replace cottonseed meal as a protein source, while cassava hull could replace corn as an energy source, without any effect on the performance of cattle.

Biochar and activated charcoal

Biochar is the residue from the carbonization of fibrous biomass at high temperatures (500 -1000°C) under a low oxygen environment. When the end product of the carbonization is activated, for example, with steam, it becomes activated charcoal. Feeding biochar or activated charcoal to animals is a recent development arising from the finding that inclusion of 1 percent of biochar in a cassava-based diet improved the growth rate of cattle and reduced the discharge of methane from the rumen.

The potential of feeding biochar to poultry, pig, and fish has been demonstrated and is associated with improvements in growth performance and reduction of odor in the farming environment. Researchers at the National University of Laos, Vientiane Capital, Lao, studied the effects of rice distillers’ by-product and biochar as additives to a forage-based diet (similar to cassava leaf meal) on growing pigs. They reported improvements in weight gain and feed conversion for the biochar and rice distillers’ by-product when added separately, but no benefits from combining both additives.  

Conclusion

In order to overcome the various compositional shortcomings identified in processed cassava waste products, their use in practical diets formulation requires the addition of essential feed additives. These essential additives include different nutrient supplementations such as proteins and amino acids, betaine, fat/oil, common salt, mineral, and vitamin premixes. Others are exogenous enzymes, organic acids, anti-toxicants, mold/mycotoxin inhibitors, probiotics, and biochar. The choice of additives to be included in a given diet will however depend on the type of animal, cassava waste, processing methods, and type of farm.

Bibliographic References

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