REVIEW ARTICLE

THE POTENTIAL USE OF ACACIA LEAF MEAL AS PROTEIN FEED SOURCE FOR POULTRY DIETS: A REVIEW

S. D. Kolobe, J. W. Ng’ambi, T. Chitura, E. Malematja, M. F.D. Nemauluma, and T. G. Manyelo^#

Department of Agricultural Economics and Animal Production, University of Limpopo,

Private Bag X1106, Sovenga 0727, South Africa

^#Corresponding author email: manyelo.tg@gmail.com;

ABSTRACT

Poultry accounts for more than 30 % of all animal protein consumption worldwide. It is estimated that by 2030, poultry will account for 41 % of all animal protein consumed by people due to low income and population growth. Protein feed sources are considered the most valuable but expensive ingredients in poultry production. High feed cost is the major problem faced by livestock and poultry farmers, especially those in rural communities. The need to search for alternative feed sources has triggered much interest in the use of Acacia meals including A. karroo, A. tortilis, A. nilotica, and A. angustissima leaf meals in poultry diets since they are readily available, grow in abundance, and cover large areas in most parts of Africa. Acacia meals have high nutritional values due to their large amounts of crude protein, hence, can effectively serve as an alternative protein feed source for the poultry diet. However, their utilisation is restricted by the presence of tannins within the leaves. Previous research on the inclusion of Acacia meals in poultry species focused mainly on broiler chicken diets. Therefore, the present review encompases the potential use of Acacia meal as a cheap and alternative protein source in poultry diets.

Keywords: Acacia meal, Tannins, Protein feed source, Poultry

https://doi.org/10.36899/JAPS.2022.6.0557
Published first online June 11, 2022

INTRODUCTION

Poultry production worldwide contributes more than 30% of protein for human consumption through meat, eggs, and their products (Hafiz et al., 2015; Motsepe et al., 2016). Rosegrant et al. (2001) reported that there is high demand for poultry meat. This is attributed to the high nutritional value and affordability of poultry meat when compared to other animal protein supplies (Hafiz et al., 2015). As a result, the poultry industry continues to grow year in and year out making it a significant contributor to global food security, income, and employment opportunities particularly for rural-based communities (Mbajiorgu et al., 2007). Seasonal changes including climate change and drought conditions affect the quantity and quality of feed raw materials which result in shortages and high poultry feed costs (Mthethwa, 2018). The hike in feed costs is mainly on protein and energy feed ingredients which adversely affect poultry industries, especially commercial and smallholder poultry farmers. Poultry meat is the most preferred meat by consumers because it is considered healthier, tastier, and cheaper than meat from other livestock (Brenes and Raura, 2010; DAFF, 2011; Hafiz et al., 2015). However, chicken meat is constrained by its high amount of unsaturated fatty acid contents, which exposes meat to lipid oxidation, leading to microbial spoilage (Wapi et al., 2013). This process causes undesirable meat with poor quality, low shelf life which also affect the price and consumer preference. (Tshabalala et al., 2003; Cunha et al., 2018; Mthethwa, 2018). Synthetic antioxidants have primarily been used to retard lipid oxidation in chickens but their continued use is, however, considered harmful to humans as they produce carcinogenic effects (Gheisari et al., 2017; Lorenzo et al., 2018). Because of this, consumers tend to shift their preference to meat produced naturally without the use of growth hormones and chemicals (Tshabalala et al., 2003; Shah et al., 2014; Lorenzo et al., 2018; Nikmaram et al., 2018; Cunha et al., 2018). These problems have triggered more research interest in finding possible alternative feed sources in the poultry industry. Thus, it is important to find alternative, low-cost, and effective feedstuffs to reduce costs while maintaining high productivity. It has been reported that most fodder trees and shrubs have high crude protein on a dry matter basis and can be used as an alternative protein source in poultry feeds to elevate bird productivity since they are affordable and readily available (Jamala et al., 2013; Tufarelli et al., 2018). In addition, other authors observed that dietary tannins inclusion from Acacia meals in diets reduced fat deposition in broiler chickens (Ng’ambi et al., 2009; Hafeni, 2013). The most common Acacia species includes Acacia karroo, Acacia tortilis, Acacia nilotica, Acacia angustissima, Acacia saligna and Acacia scaffneri. Although they have high crude protein content, their utilisation, anti-nutritional factors (amount and types of tannins), viability, and palatability need to be taken into consideration as they affect animal performance (Mokoboki et al., 2005; Anon, 2009; Hassan and Abd El-Dayem, 2019). There is limited information about the use of various Acacia meals as alternative protein sources in poultry feeds to improve productivity and reduce feed costs. The aim was to report on the potential use of Acacia meals as protein feed sources in poultry production.

Description of various Acacia species: Acacia species are leguminous trees and shrubs which remain green almost throughout the year. They are known to adapt and survive in dry, poor, and harsh environmental conditions and they are highly distributed in most parts of the world (Mokoboki et al., 2005; Mashamaite et al., 2009; Mapiye et al., 2011; Mathobela, 2018). The common Acacia species includes; Acacia karroo, Acacia tortilis, Acacia nilotica, Acacia angustissima, Acacia saligna and Acacia schaffneri.  Acacia karroo, also called Vachellia karroo, is the most widespread Acacia species in Southern Africa, where it is commonly known as sweet thorn (Mapiye et al., 2011). It adapts well to different environmental conditions (Mathobela, 2018). Acacia karroo is abundant in South Africa and grows well during the dry season, mainly in dry parts of the country (Mokoboki et al., 2005). Acacia tortilis also called Vachelliatortilis is the most common valuable thorned Acacia species which falls under Leguminaceae family. It is characterised by a twisted browny pod structure and umbrella-shaped canopy; thus, it is called an umbrella thorn (Orwa et al., 2009). It has a deep root system that enables it to tolerate heavy browsing and severe droughts, it thus adapts well to harsh conditions of arid and sub-arid areas of Africa (Mathobela 2018). Acacia nilotica has a deep taproot system with extensive lateral roots that helps it to thrive in dry areas. It is observed as a weed in some areas including some parts of South Africa. Acacia angustissima is a thornless tree or shrub characterised by a short trunk and belongs to Mimosaceae family. It can grow well in harsh environments such as prolonged drought and occasional freezing conditions. It has also been reported to recover well from frequent cuttings (Ncube et al., 2012). Many scientific studies are based on the use of Acacia meals in ruminant diets. However, information on the use of Acacia leaf meals in the poultry diet is limited. These Acacia tree species are abundant and readily available in most parts of Africa.

Nutritional value and chemical composition of Acacia species: The nutrient component, digestibility, metabolism, concentrations of essential nutrients, intake of nutrients, and the secondary compounds determines the feeding and economic value of forage species consumed by animals (Adesogan et al., 2006; Gebeyew et al., 2015). The nutritive value of tanniniferous forages such as Acacia species is determined by the amount of tannin content found within their leaves (Mlambo et al., 2009). This specifically includes; the chemical structure, molecular weight, and concentration of tannins found in tanniniferous forages (Mueller-Harvey, 2006: Mlambo et al., 2009). It is, therefore, important to consider the anti-nutritional factors such as tannin levels in Acacia leaves when feeding animals as they affect their utilization by the animals (Mokoboki et al., 2005; Brown et al., 2016). Other factors influencing the variation in the nutritional value of Acacia leaves of the same species from different trees include; population, soil, climate, stage of growth, browse pressure, and assay methods (Mapiye et al., 2011). It has been reported that most tree species-rich in natural-occurring polyphenolic compounds such as tannins contain high crude protein contents (Mlambo et al., 2015) compared to other forages such as grasses and cereal grains (Chepape et al., 2011). Some authors observed high crude protein, minerals, and fatty acids in Acacia leaves which makes them a suitable protein supplement for animals (Ngwa et al., 2002; Mapiye et al., 2011). The amount of crude protein in Acacia leaves can be utilised effectively by ruminant animals during the dry season (Marume et al., 2012) and has been reported to be high enough to meet protein requirements for broiler chickens (Mthethwa, 2018). Acacia leaves have also been reported to contain low detergent fibre which indicates a high feeding value (Mokoboki et al., 2005; Mapiye et al., 2011). Tables 1 and 2 below show the chemical composition and mineral content respectively of the leaves of selected various Acacia species.

Table 1: Chemical composition of various selected Acacia species (g/kgDM)

Sources: (Ngwa et al., 2002; Mokoboki et al., 2005; Al-soqeer, 2008; Mapiye et al., 2011; Nsahlai et al., 2011; Fuentes et al., 2012; Mbongeni, 2013; Ng’ambu et al., 2013; Zia-Ul-Haq et al., 2013; Brown et al., 2016; Ncube et al., 2017b; Mthethwa, 2018; Gudiso et al., 2019; Abd El-Galil et al., 2018; Gebremeskel et al., 2019; Aruwayo et al., 2020; Otemuyiwa et al., 2020).

Table 2: Mineral content of various selected Acacia species.

Sources: (Mapiye et al., 2011; Fuentes et al., 2012; Mbongeni, 2013; Ncube et al., 2017b; Mthethwa, 2018; Abd El-Galil et al., 2018).

Tannin composition of Acacia meals: Acacia species contain high phenolic compounds in various parts of the tree including the leaves. These compounds perform several functions including high-level antioxidant activities and plant protection against browsers (Sultana et al., 2007). Some of these compounds such as tannins are considered antinutritional. Tannins are astringent phenolic compounds found in plants or herbs (Maudu, 2010). Other researchers define tannins as a heterogeneous group of secondary metabolites that are soluble in water and polar solution (Tufarelli et al., 2017; Singh, 2017). Large and complex tannins can easily be degraded into smaller tannins by water or dilute acids in 30 minutes at a gradual increase in temperature (Mashamaite et al., 2009). Tannins have a high molecular weight that is above 500Da and are characterized by their ability to bind to form soluble or insoluble tannin-protein complexes. Unlike other phenolic metabolites, they can precipitate proteins from an aqueous solution (Al-Hijazeen et al., 2016; Huang et al., 2018). They can also form complexes with other nutrient compounds such as polysaccharides, alkaloids, nucleic acids, and minerals (Singh, 2017). In plants, tannins act as chemical defensive mechanisms to protect them against pathogens, herbivores, insects, and harsh environmental conditions (Mazid et al., 2011). Furthermore, they have been reported to perform biological activities such as antioxidant, anti-microbial, anti-parasitic, anti-virus, metal-chelating, and protein precipitation in plants (Huang et al., 2018). Factors including; plant species, cultivars, tissues, leafage, stage of development, and environmental conditions such as exposure to herbivores, nutrient stress, light intensity, and temperature determine the type and quantity of tannins found in various plant trees of the same species (Frutos et al., 2004; Huang et al., 2017). Approximately 80% of woody plants such as Acacia species contain tannin compounds (Huang et al., 2018). Furthermore, tannins are present in various feeds such as fodder, legumes, browse leaves, and fruits (Mlambo et al., 2004). They are highly concentrated in the most vulnerable parts including new leaves and flowers (Frutos et al., 2004). In addition, they are also found in many poultry feedstuffs, including sorghum, peas, and cottonseed (Nyamambi et al., 2007). According to Moyo et al. (2012) tannins found in leguminous trees are regarded as one natural antioxidant substance.

Tannins are among the important anti-nutritional factors of various browse trees, including Acacia species (Mlambo et al., 2009). Nutritional effects of tannins depend on tannin concentration, molecular weight, and structure, as well as animal factors (Mlambo et al., 2015). According to Sugiharto et al. (2019), low tannins inclusion in poultry diets has a positive impact on their health and performance. This is supported by studies that reported that low levels of dietary tannins from Acacia meals improved the growth performance of ruminants (Ng’ambu et al., 2013) and monogastric animals, more especially broiler chickens (Huang et al., 2018). Other studies observed that low tannins inclusion had no adverse effect on poultry productivity (Cui et al., 2018; Manyelo et al., 2019). However, the utilisation of tannin-rich leaf meals can further be improved by various techniques such as soaking feed with alkaline or water solutions (Nawab et al., 2020), sun drying, cooking, fermentation (Sugiharto et al., 2019), detannification process with wood ash then store at room temperature (Brown et al., 2016; Nawab et al., 2020), dilution, extraction using organic solvents, biodegradation by white-rot fungi, the use of Magadi soda containing alkalies (sodium carbonate, sodium bicarbonate, and sodium sesquicarbonate) (Ben Salem et al., 2005) and the use of binding agents such as polyethylene glycol and polyvinyl pyrrolidone to extract tannin compounds from plants and effectively assist in reducing anti-nutritional factors (Nsahlai et al., 2011).

There are two groups of tannins in plants, this includes condensed tannins and hydrolysable tannins (Maudu, 2010). They are differentiated according to their chemical structure and characteristic properties (Singh, 2017), and they can both precipitate proteins (Mashamaite et al., 2009). It has been reported that complex phenolics such as condensed and hydrolysable tannins show greater antioxidant activities compared to simple phenolics (Huang et al., 2018).

Condensed tannins: Condensed tannins (CT), also called proanthocyanidins are non-hydrolysable tannins with a condensed chemical structure (Huang et al., 2018). CT is divided into polymerized products including flava-3-ols and flava-3,4-diols or a mixture of both (Al-Hijazeen et al., 2016). Their structure consists of unbranched polymers having 2 to 5 or more flavonoid units joined by carbon to carbon linkages (van Wyk and Gericke, 2000), which can be broken by hydrolysis (Kambashi et al., 2014). CT has no carbohydrate core, however, they are derived from the condensation of flavonoid precursors without the action of specific enzymes (Ng’ambi et al., 2009). They are water-soluble polymeric phenolics with high level of phenolic hydroxyl group which allows them to bind to proteins (Ng’ambi et al., 2009) and other molecules such as metal ions and polysaccharides, thus preventing the microbial attack on proteins (Tshabalala et al., 2013).

According to Ng’ambi et al. (2009), CT compounds are found in abundance in higher plant species and are more active in precipitating proteins than hydrolysable tannins. They are also found in pastures and can be used for various purposes (Idso and Idso, 2002). CT mainly acts as a defensive mechanism in plants against herbivores (Tshabalala et al., 2013). They have a molecular weight ranging from 1000 to 20,000 Da (Huang et al., 2018). They are the most common complex phenolics found in a variety of browse sources, including leguminous forage, trees, and shrubs, particularly in the leaves and pods (Ashok and Upadhayaya, 2012).

CT has been identified as an anti-nutritional factor influencing productivity in monogastric animals (Mokoboki et al., 2005). The negative effect of high CT forages in the diets on feed intake, nutrient digestibility, palatability, protein metabolism, and animal performance are due to their ability to bind to proteins (Huang et al., 2018). Hence, CTs in Acacia leaves reduce leaf utilization by animals (Mapiye et al., 2011; Nsahlai et al., 2011; Brown et al., 2016). It has been reported that Acacia leaves contain about 4.52% DM level of CT and they tend to be beneficial at low levels when gradually included in animal diets (Ng’ambi et al., 2009).

Hydrolysable tannins: Hydrolysable tannins (HT) are ester compounds of sugar made up of glucose and phenolic acid. They consist of phenolic acids such as hexahydroxydiphenic acid and gallic acid or condensation products of ellagic acid which are partially or esterified to the hydroxyl groups of glucose (Okuda and Ito, 2011; Mlambo et al., 2015). Hydrolysable tannins are distinguished by a central carbohydrate core with several phenolic carboxylic acids connected by ester linkages (Ng’ambi et al., 2009). Hydrolysable tannins are more highly reactive to extracting solvents than CT and can be hydrolyzed by mild acids or mild bases to yield carbohydrates and phenolic acids (Mashamaite et al., 2009). However, Maudu. (2010) reported that HT can produce carbohydrates and phenolic acids through hydrolysation by weak acids or bases. They can also be hydrolysed by hot water or enzymes such as tannase (Mashamaite et al., 2009). Unlike CT, HT can be broken down in the gastrointestinal tract with ease before being absorbed by the animal (Huang et al., 2018). They have lower molecular weights (500 to 3,000 Da) and products produced from hydrolysis of HT may be the cause of toxicity in animals (Mlambo et al., 2015). Where HT are not toxic, they still influence animal nutrition by inhibiting the action of various enzymes (Yoshida et al., 2000). A variety of plants and trees can synthesize HT and most of those used as animal feeds contain low HT (Mashamaite et al., 2009).

Effect of tannins on poultry production: Tannin compounds are strongly astringent and influence palatability, intake, feed efficiency, growth rate, and digestibility in animals (Hassan et al., 2003; Kim and Miller, 2005). The responses in performance to different tannin supplementation vary depending on the type, source, and amount of tannins, the basal diet, and the animal receiving the supplementation (Patra and Saxena, 2011). Getachew et al. (2000) reported that high lignification in browse plants such as Acacia species tend to reduce digestion along the gastrointestinal tract, thus resulting in reduced animal performance. However, Reed et al. (2000) and Nawab et al. (2019) reported that high tannin content in most browse plants is one of the main factors leading to reduced animal performance. They drastically reduce feed intake by binding to dietary proteins (Mashamaite et al., 2009), cell walls, and soluble cell adhesion molecules while increasing the bitter taste of the feed material consumed by the animal (Mthethwa, 2018). The adverse effect of high dietary tannins on animal performance has been well documented (Yacout, 2016; Brown et al 2016). It has, however, been reported that tannins found in tanniniferous plants such as Acacia species can have either positive or negative effects on animal performance (Mashamaite et al., 2009). Furthermore, dietary tannins from different plant species at high, moderate, or low levels have varying effects on both ruminant and monogastric animals (Reed et al., 2000; Nawab et al., 2019).

According to Ng’ambi et al. (2009), tannins in monogastric animals such as pigs and poultry, form very complex compounds with proteins, digestive enzymes, and starch in the digestive system. The formation of tannin-protein complexes reduces protein breakdown and increases amino acid loss through excretion. According to NRC. (1994), the inclusion of high tannin in chicken diets causes nutritional problems. Moreover, the reduced feed intake due to the inclusion of plants containing tannin in the diets causes growth depression in chicks (Mashamaite et al., 2009). Other studies concluded that high dietary condensed tannin inclusion has a negative effect on the performance of broilers (Hidayat et al., 2021). In addition, the inclusion of feedstuff with condensed tannins in chicken diets before the age of three weeks has also been reported to negatively affect starch digestibility and apparent digestibility of amino acids depending on tannin levels consumed (Ng’ambi et al., 2009). Mansoori and Acamovic. (2000), also observed that dietary tannins increased the excretion of proteins, bile acids, and hyper secretion of enzymes and endogenous mineral losses in birds. Bento et al. (2005) also reported that oral administration of tannin or tannin containing material causes an increase in endogenous mineral losses in chickens.

However, monogastric animals including pigs and poultry can tolerate tannin containing feedstuff differently due to a varying number of taste buds in their mouth (Ng’ambi et al., 2009). In addition, various methods to reduce tannins from Acacia meals hence, improving their utilisation have been well documented (Ben Salem et al., 2005; Nsahlai et al., 2011; Mapiye et al., 2011; Brown et al 2016; Sugiharto et al.,2019; Nawab et al., 2020). The conclusions imposed on tannin as the main factor reducing feed intake are unfair since the reduction in feed intake can be caused by failure to consume feeds rather than the feed itself (Ng’ambi et al., 2009). Thus, studies found that the dietary intake of tanniniferous browse did not affect animal growth and performance (Mashamaite et al., 2009; Mthethwa, 2018). In addition, tannins are capable of clearing poisonous substances in animal bodies (Gxasheka et al., 2015). The supplementation of tannin rich Acacia leaf meal in goat diets improved growth performance (Ng’ambu et al., 2013). Broiler chicks can tolerate low percentage levels of dietary tannins. This is supported by Ng’ambi et al. (2009), who observed that the inclusion of low condensed tannin levels from Acacia meals can be effective in broiler diets without any harmful effects on performance, and diet intake, digestibility, and live weight of the chickens. Similarly, Manyelo et al. (2019) concluded that low tannins inclusion in the broiler diet has no adverse effect on the productivity of broiler chickens. In addition, Huang et al. (2018) reported that low to moderate tannin concentration improved health, nutrition, and performance in non-ruminants.

Table 3: Effect of tannins from Acacia meals on feed intake, digestibility, and performance in broiler chickens

Economic efficiency of using Acacia meals: Feeds constitutes a greater proportion of poultry production costs, hence, the price of each ingredient required has a greater effect on the economic efficiency (Mthethwa, 2018). The low cost of feeding with readily available and easily accessible feeds could improve both the economic and ecological viability of livestock enterprises by reducing total feed costs (Mapiye et al., 2011; Mthethwa, 2018). Access to cheap and readily available alternatives has been reported to be economically beneficial to livestock farmers due to the reduced cost of production. Thus, it is important to find economically valuable alternative feed sources produced locally to replace conventional feed ingredients, while maintaining low feed costs (Hafeni, 2013). The economic efficiency of utilizing Acacia meals in poultry diets has been reported in studies mainly focusing on broiler chicken production. Abd El-Galil et al. (2018) observed that the inclusion of 8% Acacia saligna leaf meal in Mamourah growing hens diet resulted in higher net returns, percentage of economical efficiency, and relative economical efficiency of feed, and least feed cost of kg gain compared to other inclusion levels. Hassan and Abd El-Dayem. (2019) also found that 6% Acacia leaves meal in broiler diets improved economic efficiency % of feed and relative economic efficiency of feed compared to the control diet. According to Madzimure et al. (2018), the inclusion of 50 g/kg Acacia anguistissima in broiler chickens' diet resulted in the highest net returns, consequenctly, yielding better economic benefits than other inclusion levels. However, Olerede et al. (2000) observed that a 10% Acacia nilotica seed kernel meal level to replace groundnut cake in chicken diets could be economically beneficial as it resulted in the lowest feed cost/kg and highest total revenue and economic efficiency. 

Acacia meals as a protein feed source in poultry diets: Feeding of forages can be beneficial to poultry farmers as they can reduce the dependence on the traditional protein and energy feed ingredients. Hence, various forage species, including Acacia meals can be used as alternative protein sources for livestock species (Tufarelli et al., 2018). Sugiharto et al. (2019) reported that the inclusion of leaf meals in broiler diets helps to lessen the use of protein-rich feedstuffs by partially replacing them, consequently, reducing feed costs. Some Acacia meals often used in poultry diets include Acacia angustissima, Acacia tortilis, Acacia karroo, Acacia saligna, and Acacia schaffneri. The inclusion of Acacia angustissima in broiler diets to improve growth and carcass characteristics has been well documented. This species shows a greater potential to be used as a protein feed source to partially replace common protein sources in broiler diets (Ncube et al., 2012; Ncube et al., 2017a; Madzimure et al., 2018; Gudiso et al., 2019). Ncube et al. (2015) also observed that Acacia angustissima meal can be used efficiently as a crude protein source in broiler diets when it is harvested at the mid maturity stage to maximize crude protein and condensed tannin levels. Other studies reported the use of Acacia tortilis meal in broiler diets. It was concluded that the meal can help reduce the portion of other protein ingredients in broiler diets by partially replacing them without any detrimental effect on performance and carcass yield (Miya, 2019; Ikiamba et al., 2020). Ng’ambi et al. (2009) observed that Acacia karroo leaf meals have the potential to be used as additives in poultry diets at lower levels. According to Fuentes et al. (2012), Acacia schaffneri seed meal can effectively be used in the backyard production system to partially replace expensive protein and energy feed sources in poultry diets. Abd El-Galil et al. (2018) also found that Acacia saligna leaf meal can be utilised in chicken diets without any negative effects on their performance and further recommended its use. However, there is limited information on the use of Acacia meals as a protein source in the diets of other poultry species such as indigenous chickens, ducks, turkeys, ostriches, and guinea fowls.

Conclusion: Acacia meals have been in use for more than a decade in broiler diets. Although they contain high tannin levels, they have been proven to be highly effective when partially incorporated into chicken diets. The use of Acacia meals in poultry rations will help farmers reduce the costs of purchasing commercially used expensive feedstuffs such as fish and soya bean meals. It can therefore be concluded that Acacia meals can show greater potential to be utilised safely as a protein source for broiler poultry as various meals were proven to be effective in many research papers. However, there is a need for further research on the use of Acacia meals in diets of other poultry species such as indigenous chickens, ducks, turkeys, and ostriches.

Acknowledgments: None.

Conflicts of Interest: No potential conflict of interest was reported by the authors. 

Author contribution statement: S.D.K., E.M., and M.F.D.N. writing original draft preparation: J.W.N., C.T., and T.G.M.: review and editing. J.W.N., C.T., and T.G.M.: Conceptualization, supervision, and visualization. All authors have read and agreed to the published version of the manuscript.

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