CHAPTER TWO: LITERATURE REVIEW

2.1. Introduction

Feed formulation for poultry involves a number of nutritional and economical constituents, the nutritional part includes nutritive value, availability and quality of feed ingredients, type of processing required and incorporation ratios in diets formulation. The prices and supply of ingredients, in addition to cost of preparation and marketing margins are the main economic aspects that should be taken on consideration in poultry nutrition planning (Wilson et al., 1995). Now a day the development in formulation software, mixing techniques and storing facilities move the poultry nutrition to the next step. Furthermore, promoting and using of feed additives such as premixes, preventive materials and microbial enzyme helped in raise the benefits of feed to bird even more.

2.2. Protein sources for poultry

Poultry diets protein mainly comes from animal and vegetable sources, those two categories have different protein levels with different amino acids nature and content. Plant protein sources commonly used for poultry are by-products of edible oil extraction from the “oil seeds (FAO, 20013). On other hand about 50% of the live market weight of large animals and 30% of poultry is by-product, these by-products are rendered, ground and used as source of animal protein in poultry diets in form of meals such as meat, meat &bone, blood, feather, and fish meal. Animal protein is considered as a high quality protein because of a better balance of essential amino acids, higher biological value and, easier to digest than vegetable protein sources (Ravindran &Blair, 1992; FAO, 2013).

2.2.1. Animal protein sources:

Animal protein sources are normally used in poultry diets to balance the amino acid contents, raise quality, palatability of diet, and to their important role in building animal protein tissues to produce meat and other poultry products (Cheeke, 2005), for that feed manufacturers always keep the animal protein sources on required levels in poultry diets, especially for young birds due to high amino acid requirements during this critical period of age. The requirements for essential amino acids are progressively reduced as the birds grow. Meat meal and fish meal are the most widely used animal protein sources in poultry diets, meat meal is produced mainly from dry- rendered animal tissues and bones, its contains high level of protein (53 – 55% crude protein), calcium (7 – 10%) and phosphorus (4.4 – 6%) also meat meal has a well-balanced amino acid profile and it is highly digestible (81 to 87%) (Batterham et al. 1986; Kellems et al. 1998).

Fish meal is an excellent source of highly digestible protein, average crude protein content of fish meal is (62%) with 5% calcium and 3% available phosphorous, although the high nutritive value of fish meal but it always used in small amount in poultry feeds specially in layer diets, due to its smell and physical and chemical interactions (Chadd, 2008).

Blood meal is a good source animal protein it can be used successfully in poultry, while feather meal contains high unavailable protein with relatively poor digestibility, so it is not commonly used as protein resources for poultry as well as the poultry by-products meal which may be obtained from unhealthy birds is classified as high-risk material, and may transmit diseases to poultry.  Incorporation animal protein sources normally recommended to be less than 10 percent in poultry diets, due to specific limitations assigned to these products regarded to their nutrients availability and contents (Kellems et al. 1998).

2.2.2. Vegetable protein sources:

Protein supplements constitute the largest component of poultry diets. Plant protein sources supply most of dietary protein required for poultry feed formulation, which usually contains vegetable protein source in form of oilseed industry by-product, however, vegetable protein sources can be introduced in poultry diets as raw materials or legumes such as dry beans.

Soybean meal (SBM) is a commonly used vegetable protein source worldwide, followed by canola meal (CM) (Leeson &Summers, 2001),  it  is consider as the major source of dietary protein in broiler diets at different geographical areas and/or in different seasons, however other protein meals are sometimes available at competitive prices and are thus preferentially used in least-cost formulations (Aftab 2009). There are a number of reasons that SBM dominates the protein supplements market for poultry including high nutrient content, availability year round, and high content of crude protein with high total and digestible amino acid content, also there is no common plant protein feedstuff exceeds soybean meal in digestible energy content (Sara 2003). Crude protein content of SBM range between (40 – 48%), digestible energy (14.9 -19.5%), with  relatively low crude fibre content (4.2 – 5.5%) depending on the degree of hull removing and the oil extraction procedure in comparison to other vegetable protein sources (Karr-lilienthal et al., 2004).

Using of canola meal in poultry feeds has been growing rapidly in recent years, due to increased amount of grown and processed canola, low prices, and high crude protein content, high digestibility, in addition to that it considered as a good source of energy, calcium and available phosphorous, canola meal contains (35-37.5%) crude protein, (11-12%) crude fibre, (0.6 -0.7%) calcium, and (0.45 -0.5%) available phosphorous (Khajali &Slominski, 2012).

Cottonseed meal (CSM) and sunflower seed meal (SFM) considered as alternatives to SBM and CM for poultry diets formulations, despite their high protein and energy contents, but CSM and SFM are not widely used as main sources of vegetable protein in poultry diets, due to their high fibre content, low digestibility, imbalanced amino acid content, and presence of some nutritional inhibitors and anti-nutritional factors in this ingredients (Nagalakshmi et al., 2007). Sesame seed meal is a good quality oilseed cake meal it considers as a good source of protein with high methionine content, but its high content of phytate, availability in economic quantities limiting the use of this plant meal as alternative protein source for poultry (Raju et al., 2007).  Potential for mycotoxin contamination (aflatoxin), availability, threonine deficiency, and high tannins content limited the incorporation of peanut meal in poultry diets, although it has high crude protein content. (Pesti et al, 2003).

2.2.3. Nutritive value of alternative vegetable protein sources:

There is a number of oil industries by-products successfully replaced soybean meal and canola meal as sources of vegetable protein for poultry such as CSM and SFM, although some of these by- products are widely used in diets for family poultry production level. Nutritive value and/or concentration of nutrients in vegetable protein sources depends on the variety of cultivars, ways of decortication, methods of oil extraction, proportion of kernel to husk, lint and seed coat (Nagalakshmi et al., 2007). Ravindran &Blair, 1992 summarized nutritional aspects or factors that limiting the use of alternative vegetable sources in poultry diets worldwide into; variability (or lack of consistency) in nutrient quality, limited information on the availability of nutrients, high fibre content, presence of anti-nutritional factor(s), and need for nutrient supplementation (added cost). Most of alternative vegetable protein sources contain high crude protein content, high crude fibre, and relatively high energy content, besides it consider as an important source of micro-nutrients such as vitamins and minerals (Elbushy & van der Poel, 1994).

 2.2.3.1. Protein content and amino acid balance:

The average crude protein content of oilseed meals varies from 32% in sunflower to 48% in soybean meal. Crude protein content of commercial cottonseed meal ranged between (22 – 56%), depending on the method of oil extraction, the value being slightly higher in decorticated CSM (34.1 – 56.1% than un-decorticated (22.2 – 30.3%) (Reid et al., 1984; Ryan et al., 1986; NRC, 1994), CSM protein deficient in methionine, threonine, valine, and lysine compared to SBM (Salas et al, 2013), it contains only 58% of the total lysine and 43% of the digestible lysine of SBM (Lordelo et al, 2004). Sharma et al. 1978b reported that protein digestibility of un-decorticated and decorticated cottonseed meals are 42 and 41% respectively. Cottonseed meal contains gossypol, unless it has been obtained from glandless (gossypol-free) seeds, presence of gossypol (polyphenolic compound) and cyclopropenic acids has a toxic effect on poultry, because gossypol reduces the digestibility of protein indirectly through reaction with free amino groups of basic amino acids particularly lysine or through direct inhibition of certain enzymes present in the bird gastrointestinal tract (Baliga et al., 1959; Sharma et al., 1978b; Nagalakshmi et al., 2007).

Protein and amino acids profile of sunflower meal reveals that it contains approximately (20- 40%) crude protein depending on the de-hulling and oil extraction process (Senkoylu et al, 1999; Crum et al., 1993; Mushtaq et al., 2006; Gonzalez-Perez &Vereijken, 2007), rich in tryptophan, arginine, and deficient in lysine, methionine and cystine depending on the maturity of seed at harvesting time (Nesheim et al., 1982). Sunflower meal is composed from (34-40%) hull and 60- 65% protein core (kernel) (Daghir et al. 1980).

Protein content of peanut meal relatively similar to soybean meal (47 – 48%) with high arginine content, but it contains less lysine and threonine when compared to other vegetable protein sources (Costa et al, 2001). Researches showed that the protein content of sesame meal range between (45-52%), with high methionine and low lysine contents (Kanekol &Yamasakil, 2002; (Mamputo &Buhr, 1995).

2.2.3.2. Energy content and utilization:

Cereal grains provide 60-70% of dietary energy for poultry, protein sources may also supply considerable amount of energy, and also their interaction with the main energy sources has an effect on overall energy supply and feed utilization. So, it is important to determine precisely energy values of diets containing vegetable sources, either for least–cost formulation purposes or for adapting feed supply to energy requirements of animals (Noblet, 2006).  Since the true metabolizable energy (TME) equal gross energy of the feed minus the gross energy of the excreta of the food origin, TME are believed to be more descriptive to feed energy available for chickens than apparent metabolizable energy (AME) value, because procedures used in the TME determination inherently correct for variations due to differences in feed intake and may reduce some of the variation between species and strains of chicken. Researchers reported that there is considerable differences in metabolizable energy content of cottonseed meal for poultry ranging from 1857 – 2600 kcal/kg which reported by (Sibbald, 1976; Yamazaki et al., 1986; Papadopoulos et al., 1987; NRC, 1994; Fernadez et al, 1995) to 4961 – 5119 kcal/kg kcal/kg ( Sallas et al, 2013) and  7.94 – 9.13 MJ/kg-1 (Nagalakshmi et al., 2007), this big differences attributed to the residual oil contents and improper handling of oilseeds during storage and processing . Sallas et al, 2013 stated that the gross energy content of CSM ranged between. Regarding the previous reasons the high fibre content of SFM also may affect its gross energy and TME contents for poultry which are ranged between 4406. – 5017 kcal/kg, and 3170 – 3297 kcal/kg respectively (Senkoylu &Dale, 2006; Grompone, 2005).

Groundnut meal provides average of 11.9 MJ/kg metabolizable energy and 20.4 MJ/kg gross energy for poultry, while the average ME and gross energy contents of sesame meal are 11.2 MJ/kg and 20.5 MJ/kg respectively (Nwokolo, E., 1986; Huque et al., 1996). The big variations of energy values between oil seed meals may attribute to variations in oil seed types, processing methods, anti-nutritive factors, and amount of fat contents. There are many factors affecting the utilization of feed energy in optimal way therefore, limit or decrease the nutritive value of feeds to poultry.

2.2.3.3. Other nutrients:

Crude fibre content of commercial cottonseed meal is higher (25%) than de-hulled CSM meal (12.88%), calcium and available phosphorus contents for both meals are almost similar (0.24 – 0.29%), and (0.77 – 0.94%) respectively (NRC, 1994; Reid et al., 1984). Studies reported that sunflower seed meal derived from different varieties of sunflower seeds contains high level of fibre (14 -32%), also it consider as a valuable source of calcium, phosphorus it contains calcium (0.22 – 0.30%) and (0.28 – 0.50%) available phosphorus (Zattari and sell, 1990; San Juan & Villamide, 2000; Villamide & San Juan, 1998; Senkoylu, &Dale, 1999). In DM basis the average crude fibre content of peanut and sesame meals are 11.7 and 7.8 g/kg, respectively (Nwokolo, E., 1986; Huque et al., 1996; Jacob et al., 1996).

 2.2.4. Biological value of vegetable proteins:

The protein quality can be evaluated through  amino acid score (AAS), nitrogen balance, in vitro or in vivo protein digestibility, protein efficiency ratio, net protein ratio, protein rating, net protein utilisation, and biological value (Boye et al, 2012). The biological value (BV) of a protein is related directly to the efficiency of protein utilisation and measures the body absorption and utilization of protein, the protein from animal sources has higher BV than that of vegetable origin. The biological values of vegetable protein sources are differ due to protein and amino acid contents. Bamgbose (1995) observed that cottonseed cake biological value was 51.0% compared to 61.0 and 73.0% for defatted and full-fat extruded soybean, its considered substantially higher compared to other vegetable protein sources excluding soybean and canola proteins.

2.2.5. Availability and commercial utilization of vegetable protein sources:

The shift of human consumption towards consuming vegetable products more than animal foods lead to increase production of oilseeds such as soybean, canola, sunflower, cotton seeds…etc., as result large amount of oilseed meals are produced as by-products of oil extraction process, so these oilseed meals are available to use in animal feeds. Soybean meal constitutes the common and widely used vegetable protein sources around the world, because of its good and highly digestible protein, with good balance of essential amino acids, which can complement most cereal-based diets. In addition to that the amino acid availability in soybean meal is higher, and the metabolizable energy content is also higher than in other oilseed meals. Although the soybean production has increased substantially over the past two decades to meet the rising demands, but till now there is a shortfall between soybean production and consumption around the World. As result the production and utilization of canola, sunflower, cottonseed and other oil seeds cake has been increased to meet market demand for oils and cakes; moreover affordability, accessibility, and ease of processing for poultry industry make these vegetable protein sources more attractive for feed formulation (Vieira et al 2003), so availability of high quality and low price vegetable protein sources are important elements to maintain poultry production competitive and continue to provide animal protein for human consumption. Other vegetable protein meals are sometimes available at competitive prices and are thus preferentially used in least-cost diet formulations, in this case the maximum safe level of inclusion of these protein meals in diets for different classes of poultry is often a concern ( Aftab 2009).

There are many factors affecting the availability of vegetable protein sources for commercial using such as climate changes, seasonality of production, cultivation, prices fluctuations, digestibility and nutritive value, and potential competitors, so farmers and feed mill owners challenged to select feed ingredients to use for poultry without compromising the quality of the feed, performance of the birds, and economics of production (Oluyemi et al, 2000; Ravindran &Blair, 1992; Ojewola et al, 2006).  In terms of availability, feeding response, protein quality and safety aspects, storage and marketing cottonseed and sunflower seed meals are most traded vegetable protein sources for poultry excluding soybean and canola meals (USDA, 2000). From availability and food security point alternative vegetable proteins can play a more significant role in satisfying poultry producers and food protein demand in future.

2.2.6. Trends in utilization of alternative vegetable protein sources:

It is known that the formulation of poultry feed is mainly based on soybeans as vegetable protein sources however, its variable availability depending on region and time of year, this leads to variations in feeding cost , which directly affecting the profitability. Therefore, an alternative to increase efficiency in poultry production is to use alternative vegetable protein sources to replace soybeans in feed formulation (Bell &Weaver, 2002).

Most of alternative vegetable protein sources for instance cottonseed and sunflower seed meals are commonly used as sources of vegetable protein for ruminants, especially in sunflower and cotton-producing areas such as India, China and the USA, where it is used as a partial substitute for soybean meal. Alternative protein sources do not completely replace soybean meal, because they do not demonstrate greater weight gains; less feed consumed or better feed conversion than soybean meal when fed to poultry alone (Hamilton, 2002). The interest expressed on cottonseed meal is greater than others, because, as already mentioned, cottonseed meal availability decreases shortage risks assumed when one uses an alternative protein source and ensures a higher quality level than the other sources. Sunflower has a great capability to adapt to different climatic and soil condition, therefore it cultivated worldwide for oil extraction. Earlier reports illustrated that sunflower meal is an adequate source of supplemental protein in chick starter diets (Ravindran &Blair, 1992).

2.2.7. Cotton seed meal as a vegetable protein source for poultry:

The main products derived from cottonseed are cotton seed oil (16%), cotton seed hulls (25%) and cottonseed meal (45%). Cottonseed meal is a residue of oil extraction from cottonseeds, through a number of practical methods of oil extraction from cottonseed such as mechanical extraction, direct solvent, and pre-press solvent extraction, as result there is a wide range of cottonseed meals differing on their protein, fibre and oil content (Jones, 1985: Rostango et al, 1995). Presence of gossypol, cycloproponoic fatty acids, and high fibre content in cottonseed meal affect protein quality and limit the use of cottonseed meal as a major vegetable protein for poultry.

Chemical composition of CSM (on dry matter basis) has been reported by several researchers as; 22.2 – 56.1% CP, 7,9 – 11.8% MJ/kg ME, 15.9 – 28.5% CF, 5.2 – 8.9% ash, and 2.1 – 7.3% ether extract  (Foley et al.,1972; Reid et al., 1984; Ryan et al., 1986; NRC, 1994; Watkins, &Waldroup, 1995; Nagalakshmi et al., 2007). Previous studies showed that the amino acids composition of various CSM deficient in methionine, available lysine, and threonine contents compared to arginine and other amino acids contents (Sharma et al., 1978a; Reid et al., 1984; Ryan et al., 1986; El Boushy and Raterinik, 1989; NRC, 1994).

Cottonseed meal did not completely replace soybean meal, but it has been suggested that CSM supplemented with lysine can be introduced in broilers diets to replace soybean in limit of 10%, 20% and 30% (Sharma et al., 1978b; Watkins et al., 1993; Elangovan et al., 2003) 15% (Campbell, 1988), and 8%, 15%, 16% and 24% of soybean in commercial chicks diets (Campbell, 1988; El Boushy and Raterinik, 1989), while incorporation of cottonseed meals in high levels 30% and over has a negative effect on poultry performance and diet quality. Numerous researches reported that low levels of cottonseed meal has been used in layer diets to replace soybean 5%, 6%, 7.5%, 8%, 10% and 15% (Waldroup &Goodner, 1973; Raid et al, 1984; Raid et al, 1984; Panigrahi et al, 1989, Chao et al, 2014), this may attributed to pinkish discoloration of albumen and/or egg yolk mottling due to presence of cycloproponoic fatty acids in cottonseed (Phelps, 1966). Instead of replacing soybean meal, in some areas where groundnut commercially produced such as some African countries, cottonseed meal has successfully been used to replace between 50 – 75% of groundnut in groundnut based diets ((Nzekwe and Olomu, 1982). The general recommendation is to use cottonseed meal as a source of vegetable protein in poultry feeds at rates up to 15 %, with careful attention paid to lysine in feed formulation. Higher rates can be used when cottonseed meal has an economic advantage, with a risk of lower feed efficiency. In this case iron supplementation is recommended, as well as lysine supplementation.

2.2.8. Potential value and utilization of cottonseed meal:

There is a notable variations in nutritive value of cottonseed meal for poultry depending on methods of cultivation, handling and processing (collection, preparation and de-hulling, and oil extraction), and storage conditions. Presence of gossypol, cycloproponoic fatty acids (CPFA), low protein quality, and high fibre content especially in un-decorticated or partially de-hulled CSM are the most important limitations of CSM utilization for poultry. Gossypol is a polyphenolic compound present exclusively within discrete bodies called pigment glands located mainly in the endosperm of the seed, either present in form of free (FG) or bound gossypol (BG), FG more toxic to monogastric animals than BG. Inclusion of CSM in poultry diets largely depends on the amount of free gossypol in CSM, so in order to use it in poultry diets a lot of researches have been done in order to reduce and detoxify the free gossypol of CSM (Clawson et al 1961; Tyani et al, 1986; Watkins et al., 1994). Nagalakshmi et al., 2007 concluded that protein quality and quantity, proportion of hulls and the concentrations of FG and CPFA are the major factors that should considered while incorporating CSM in poultry diets, these factors depended on the variety of cultivar and methods of processing of the seed for oil extraction.

Various efforts has been done to eliminate bad effects of CSM utilization limiting factors to enhance nutritive value of CSM to make it a whole some protein supplements, these are include: physical treatment by soaking CSM in water or through heating and/or cooking for different times (Mayorga et al., 1975; Shah et al,1986) , chemical treatment by introducing metallic ions of Ca and Fe to reduce toxicity of free gossypol (Waldroup and Goodner, 1973; Panigrahi et al., 1989; Nagalakshmi et al., 2001), biological treatments through fungal fermentation (Aduku and Sell, 1986; Zhang et al., 1990), solvent extraction using some organic solvents such as ethyl alcohol, hexane, and aqueous acetone to solve the toxic materials in CSM (Damaty and Hudson,1975; Liu et al.,1981; Hron et al., 1994), biotechnological approaches by producing low FG content glandless cottonseed varieties by  genetic modification (Reid et al., 1984; Ryan et al., 1986; Mandal et al., 2004) fortification with Lysine since lysine is a first limiting amino acid in CSM (Ryan et al., 1986;Campbell,1988; Watkins et al.,1993), supplementation with vitamins to compensate decrease in antioxidant such as α-tocopherol, ascorbate and glutathione peroxidase (Bender et al.,1988; Janero and Burghardt,1988), and supplementation with microbial enzymes to increase digestibility (Aftab, 2009).

Incorporation of cottonseed meal up to 10-15 % in broilers diets considered to be safe and not affected the general performance (Herms et al., 1983; El Boushy et al., 1989; Fernandez et al., 1995), however some published reports showed that broilers performance decreases even at lower inclusion rates, while others found that performance was maintained above 20 % of CSM inclusion (Gamboa et al,. 2001; Azman et al 2005). Higher inclusion rates of cottonseed meal supplemented with iron and lysine can be used in broilers diets when cottonseed meal has an economic advantage, with a risk of lower feed efficiency. Previous studies on effect of cottonseed meal in broiler performance concluded that growth of broilers was not affected even up to 15% but the feed conversion efficiency was affected even at 15%. Dietary incorporation of commercial CSM at level of 20% in broiler chickens diets resulted in decreased body weight gain and poor feed conversion efficiency during 0 – 21 days of age (Sharma et al., 1978a; El Boushy and Raterinik, 1989; Watkins et al., 1993; Henry et al., 2001).

The effects of cottonseed meal on laying performance depend on the experimental conditions, and on the free gossypol content (Nagalakshmi et al., 2007). Some publications reported a decrease in laying performance at inclusion rates as low as 2.5 % cottonseed meal, while others showed good performance in up to 20 % cottonseed meal (Adeyemo et al., 2008). General recommendation is to limit using cottonseed meal to 10 % in layer diets, and to add iron when more than 5 % cottonseed meal included in the diet. Higher levels (15 %) can be used when egg yolk coloration problems do not have marketing consequences. The results of (Lordelo et al, 2004) suggested that broiler breeder pullets reared on a diet containing CSM as major protein source showed improved flock body weight uniformity and normal reproductive performance; however cottonseed meal was tested successfully at 25 % inclusion rate in broiler breeders, with no detrimental effect on performance and on the quality, fertility and hatchability of eggs.

2.3. Constraints to use of alternative vegetable protein sources:

Vegetable protein sources for poultry are known to have many constraints, namely presence of anti-nutritive factors, lower protein quality, deficient in essential amino acids or protein and amino acids imbalance, lower biological values, higher rate of indigestibility, poor digestibility of some vegetable protein sources, losses of quality in storage condition and so forth. These constraints inhibit the birds to utilize the feeds more efficiently and deprive them from getting full nutritional benefits, consequently poor poultry performances (Bryden et al., 2000, Akande et al., 2010; Hossain et al., 2011).

2.3.1. Nutrient balance:

Nitrogen content and protein quality of feeds depend on content of amino acids and their availability, digestibility, and further physiological utilization after digestion for some specific amino acids (Bryden et al., 2000; Bryden &Li, 2003), so vegetable protein sources evaluation for poultry depends on lysine content, methionine, and tryptophan, these essential amino acids called the major three limiting amino acids (McDonald et al., 2002). Many reports showed that vegetable protein sources contain imbalanced amino acids content, however single vegetable protein source may contains all essential and non-essential amino acids, but either not available in suitable ratio or not in enough amount for animal requirements (Sing &Panda, 1992). NRC, 1994 emphasized that soybean meal supplied all essential amino acids with exception of  sulphur amino acids, all plant protein sources have specific amino acids deficiencies, sunflower meal markedly deficient in sulphur amino acids with low lysine content, canola meal has no enough amount of lysine, cottonseed meal is deficient in lysine, methionine and leucine, and groundnut meal has low contents of lysine, threonine, and sulphur amino acids (Sing &Panda, 1992; Villamide &San Juan, 1998).

2.3.2. Anti-nutritive factors:

Anti-nutritional factors (ANFs) may defined as those substances generated in natural feedstuffs by the normal metabolism of species, and by different mechanisms such as inactivation of some nutrients and diminution of the digestive process or metabolic utilization of feed, which exert effects of contrary to optimum nutrition (Checke &Shull, 1985), these substances which either by themselves or  through their metabolic products, interfere with food utilisation resulting in reduction of protein digestibility and binding to various nutrients, and affect the health and  production of animals accordingly (Huisman &Tolman, 1992). Liener, 1989 summarized anti-nutritional factors present in plant feedstuffs into four major groups as; proteins group which includes protease inhibitors, haemagglutinins, toxic amino acids, and food allergens, glycosides group each anti-nutritional factor in this group contains CHO and non-CHO moiety (aglycone), toxicity of this group results from aglycone release during enzymic degradation, this group includes goitrogens, cyanogens, saponins, and strogens, phynols group which includes gossypols and tannins, and the last group is miscellaneous which includes non-starch polysaccharides, anti vitamine, phytic acids and toxic fatty acids. Anti-nutritional factors diminish animal productivity but may also cause toxicity during periods of scarcity or confinement when the feed rich in these substances is consumed by animals in large quantities (Kumar, 1992).

2.3.2.1. Non-starch polysaccharides:

The nutritive values of all-vegetable feeds are highly affected by indigestible carbohydrates, soybean, canola, and sunflower seed meals proteins are rich in galacto-oligosaccharides and pectic polysaccharides (Kocher, 2002). Non-starch polysaccharides (NSPs) are found in almost all ingredients of vegetable origin, depending on the physiochemical characteristics of these NSP, many have been shown to possess various anti-nutritional activities (Bedford,1993), these considered as anti-nutritive factors which affect birds performance and vegetable protein digestibility. Generally presence of anti-nutritive factors and NSPs decrease the nutritive value of vegetable feedstuffs such as SBM, CM, peas, depend on their NSPs content (Castell et al., 1996; Dale, 1996; Meng et al., 2005). The majority of NSPs in these feedstuffs are cellulose and pectic polysaccharides (Bach Knudsen, 1997), Other NSPs include rhamnogalacturonan, raffinose, and stachyose with associated side chains consisting of arabinose, galactose, and xylose residues (Bacic et al., 1988; Leeson and Summers, 2001). Other polysaccharides include cellulose, xylans, arabinoxylans, and xyloglucans, are mainly present in the hull fraction of soybean, canola and peas. Microbial fermentation in the large intestine and ceca required to digest these indigestible carbohydrates, because it is not hydrolyse through the pancreatic enzymes in the small intestine of chicken (Choct et al.,1996), because poultry lack specific enzyme systems to target these NSP, the development and evaluation of NSP-degrading enzymes has attracted much researchers attention (Aftab, 2009).

2.3.2.2. Phytate:

Phytic acid (myoinositol 1, 2, 3, 4, 5, 6-hexakisdihydrogene phytate) is found in cereals and legumes, it is the primary phosphate reserve in most seeds, highly strong and potent compound found in all oilseed cakes and plant meals, and its activity lead to form protein and mineral-phytate bond which results in reduce bioavailability of protein and minerals (Leeson and Summers, 2001; Al-Kaiesy et al., 2003).Since phytate normally found in all plant origin feedstuffs as a phosphorous reservoir during seed germination and acts as guard against oxidative stress during live of the seed, for  that the  phytate phosphorus become unavailable to non-ruminant animals including poultry, due to lack of endogenous phytases, accordingly inorganic phosphorus has to be added to poultry diets (Doria et al., 2009). All Vegetable proteins sources particularly canola meal contains relatively high phytate contents average 76.4 % of total Phosphorous (Selle et al., 2003).

2.3.2.3. Ingredient-specific anti-nutritive factors:

Each one of commonly used vegetable protein sources for poultry contains single or more specific indigenous anti-nutritional factors which hamper its proper nutrient utilization. The most important anti-nutritional factors in soybean meal are protease inhibitors (trypsin and chymotrypsin) and lectin (phytohaemagglutinins) which have the ability to binds to the epithelial cells lining the small intestine leading to interference with nutrients absorption , in addition to that soybean meal contains less important  anti-nutritional factors such as elastin, phytic acid, saponins, estrogenic factors, and anti-vitamin E, A, D, B12 factors, all these anti-nutreints cause substantial reductions in soybean meal protein and amino acid digestibility due to their ability to inhibit digestive enzymes or bind to proteins, thus reducing protein solubility and hydrolysis by digestive enzymes (liener, 1989; Tacon, 1992; Campbell &Van der Poel, 1998; Leeson &Summers, 2001; Siddhurajo et al., 2002).

Glucosinolates is important anti-nutritional factor in canola meal which reduces the deit palatability and decrease birds growth and production; also canola meal it contains tannins which forms complexes with dietary protein and carbohydrates as well as inhibits the activity of various digestive enzymes to lower extent, trypsin, saponins, erucic acid and phytate.  Gossypol is a first effective anti-nutritional factor presence in cottonseed meal which binds free amino group of essential amino acids especially lysine resulting in more toxic substance to monogastric animals, cottonseed meal also contains phytic acids, and estrogenic factors.  Although sunflower meal seed are not known to have specific anti-nutritional factors, some researches showed that it contains a number of anti-nutritional factors such as trypsin, tannins, saponins, and arginase inhibitor. On other hand groundnut meal possess many anti-nutritional factors includes trypsin, chymotrypsin, plasmin, thiamine factor, cyclopropenoic acid and saponins, beside that aflatoxins contamination in groundnut is still a threat to the poultry industry and results in substantial economic losses to producers because of its toxic effects. Phytic acid is a common anti-nutritional factor in all vegetable protein sources (liener, 1989; Warenham et al., 1994; Senkoylo &Dale, 1999; Thrope &Beal, 2000; Leeson &Summers, 2001).

2.4. Improving vegetable protein and diet quality

2.4.1. Plant breeding

Improving nutritive value of vegetable protein sources through genetic modification using conventional breeding approaches and/or modern biotechnology including genetic engineering may not give only high animal performance and health, but also lower feed costs and more affordable livestock protein products (FAO, 2004). Improvement efforts will focus on protein quality (particularly amino acid balance), better digestibility (especially of fibre and starch) and greater metabolizable energy (from improved oil content), with less anti-nutritional factors (such as phytate). High lysine, high oil, and low-phytate maize, high oleic acid and high methionine soybeans, and glandless cotton seed are successful examples of nutrient enrichment of plant feedstuffs. The principal goal of these breeding strategies is to enhance the nutritive values of the crops, by promoting the nutrients status (e.g. protein, indispensable amino acids, minerals, or fatty acids), or reducing the level of detrimental effects such as phytate in seeds (Swiatkiewicz and Arczewska-wlosek, 2011). As a result of advances in crop breeding researches, application of high available phosphorus maize in poultry diet resulted in increased availability of P compared to conventional maize, and better production indices in broilers through drastically reducing phosphorus excretion in the excreta (Waldroup et al., 2000; Yan et al., 2000). An increase level of energy and digestible amino acids was observed in low-phytate soybean meal, compared to traditional soybean in trials on duck (Adeola, 2005).  Production of glandless variety of cottonseed through genetic modification is one of the recent trends to reduce free gossypol content more than regular CSM (Reid et al., 1984). (Gonzalez-Delfino, 1971) reported that glandless CSM supported egg production equal to or better than that obtained with SBM control diet. The incidences of egg yolk discoloration were reduced and gossypol was not detected in egg yolk of hens fed glandless CSM (Ryan et al., 1986).  To what extent these developments will be widely adopted in practice will depend on many factors, including economics and market acceptance. Although genetically modified (GM) crops have demonstrated an improvement in nutritive value and thereby improved productive performance of animals, their safe use in feeding and the impact on consumer health are not completely known.

2.4.2 Ingredient processing

The main objectives of all effective feed processing techniques are to deactivate or reduce anti-nutrients and to enhance the nutritive value of feedstuffs (Akande et al., 2010). Numerous feed ingredients processing techniques has been tested in practical diet formulation, particularly for non-ruminants to effectively eliminate the toxicity of feedstuffs these processing techniques include drying, chopping, heating, pelleting, freeze drying, grinding, mealing,, ammonia treatment, autoclaving, steam treatment, boiling, cooking, refrigeration, sterilization, blanching, ensiling, chemical treatment, extracting, irradiation, and salting (Singh and Panda,1992; Leeson and Summers, 2001), also there are many reported feed ingredient processing techniques to enhance the nutritive value of whole oilseeds include extrusion, roasting, toasting, and jet-sploding (Arieli, 1998; Chen et al., 2008). As results of these techniques soybean anti-nutritional factors can be eliminated by heating, negative impacts of NSPs reduced through ethanol extraction process, nutritive value of canola meal can be enhanced by microbial breakdown of glucosinolates, and fermentation reported to decrease free gossypol content of cottonseed meal. Also gamma irradiation was reported to enhance the nutritional quality of oilseed for broiler chickens, to increase intestinal digestibility of protein and inactivate and/or remove certain anti-nutritional factors (Coon et al., 1990; Leske et al., 1993; Leeson and Summers, 2001; Siddhuraju, 2002; Farkas, 2006; De Toledo et al., 2007; Gharaghani et al., 2008; Shawrang et al., 2008).

2.4.3 Nutrient supplementation

High fibre content of some vegetable protein sources affect their digestibility so there are many feed additives used to improve these feeds for poultry such as synthetic amino acids, fat and vegetable oils, vitamin and mineral premixes, antibiotics, all these feed supplementations in addition to growth promoters, antioxidants, and other additives such as flavour enhancers, artificial and nutritive sweeteners, and colours can be included in broiler chickens diets safely to raise general performance and productivity.

Production of low quality feeds has created variety of problems for the broiler industry resulting in poor performance and lower economical returns. Some valuable nutrients in feed are wasted because the birds are not able to utilize them, this may be due to several reasons like lack of digestive enzymes, insufficient time for digestive activity, sub clinical infection and inadequate processing of feed ingredients (Haq et al., 1990). Addition of iron or ferrous sulphate to layers diets containing CSM partially prevented depression in egg production, completely alleviated the adverse effect on egg weight, and prevented egg discoloration, these due to combination of free gossypol with ferrous ion (Waldroup and Goodner, 1973), also the effect of gossypol can be removed or prevented  by supplementing antioxidants such as α-tocopherol and β-carotene in diets, because the effect of gossypol on animals may be related to the formation of free radicals or a decrease in concentration of antioxidants (Willard et al., 1995). Amino acids in organic feeds should be from non-synthetic sources only, but there is an exception granted for synthetic DL-methionine, because DL-methionine is critical in poultry diets for feathering and cell development, (Colibar, 2000) reported that supplementation of synthetic DL-methionine or probiotic addition improved the productivity and general performance of broilers, in addition supplementation of some synthetic essential amino acids such as lysine and L-threonine is a common practice in poultry diets formulation to compensate deficiencies of these essential amino acids in most vegetable protein sources. On other hand exogenous enzymes supplementation have been found to improve the nutritive value of vegetable proteins, and thereby increased performance of poultry, also enzymes have clearly been demonstrated to increase the digestibility of poorly digested diets to a much greater extent than well digested diets (Classen et al., 1995; Scott et al., 1998; Rosen, 2006). Recently new feed additives have been used to save and improve the nutritional quality of feeds such as anti-microbial contamination, mycotoxin binders, digestibility improvement agents, palatability increasing additives, fly controllers, and intestinal healthfulness additives such as coccidiosis.

2.4.4 Microbial enzyme supplementation

High fibre content of alternative vegetable protein sources appears to be the most problematic factor concerning their inclusion at high levels in poultry diets, also poultry lack specific enzyme systems to target NSPs, these reasons has attracted much attention of researchers to develop and utilize microbial enzymes to increase digestibility of poorly digested diets (Scott et al., 1998). Enzymes are added to facilitate the breakdown of larger molecular structures of the feed ingredients into smaller ones by their specific action and making these nutrients more readily available to the digestive system for better absorption. Successful attempts had been made to eliminate disadvantages of poorly digested feedstuffs by microbial cellulases and xylanases (Singh et al., 1990, Swain et al., 1996). The supplementation of animal feed with exogenous enzymes can improve the nutritional value of feed ingredients and increase the efficiency of digestion however, the use of phytase has been shown to be advantageous in the majority of cases, and the use of carbohydrases and proteases occasionally results in apparently inconsistent responses (Adeola &Cowieson, 2011). Sorensen, 1996 concluded that supplementation of SFM based diets with microbial enzymes increased the nutrients utilization by layers and broilers.

There are many published reviews discussing the efficacy of microbial enzymes in animal feeds, most of these researches are focused on increasing amino acids digestibility through degradation of anti-nutritional factors or hydrolysis of NSPs of high fibrous diets and improving  growth performance of poultry, the best examples of successfully used microbial enzymes to eliminate anti-nutritional factors and to achieve these benefits are; using of phytase  to hydrolyse plant phytate, fungal α-galactosidase to hydrolyse galacto-oligosuccharides of soybean and canola meals, and addition of protease and amylase to diets containing SBM or CM to improve the utilization of protein and assist the endosperm starch digestion in the upper gastrointestinal tract of broilers (Slominski, 1994; Simbaya et al., 1996;  Bedford, 2000). Benefits of using glyconases such as xylanase and β-gloconase in broilers diets based on cereal grains is also considered as best examples of utilization of microbial enzymes to improve vegetable protein digestibility and rise diet quality. Marsman et al, 1997 and Zanella et al. 1999 demonstrated that the addition of commercial enzymes to a corn/SBM based broilers diet significantly improved weight gain and feed conversion ratio, the increase in performance was related to an increase in ileal digestibility of crude protein, starch and fat as well as improvement in ileal digestibility of NSPs.

2.5. Importance of this study

There have been many researches conducted to evaluate alternative vegetable protein for poultry diets formulation including using constrains, different treatments to improve nutritive values, and nutritional and economical evaluation to use as sole protein source for poultry, but there are limited number of researches on safe inclusion rates of these important ingredients and their efficient to replace soybean particularly with supplementation of microbial enzymes. The current research has been designed to test the potential value of cotton seed meal (CSM) and sunflower seed meal (SFM) in diets for broiler chickens, especially when supplemented with new-age microbial enzymes, e.g. Axtra XAP and Axtra XB. From the review, those two important vegetable ingredients are considered in the top four vegetable protein sources worldwide in terms of quantity and production, protein content, and geographical growing area, in addition to that these alternative vegetable protein sources are not only safe but they have low prices and would be preferred in family, medium and large scale poultry production.

Since the experiments of this study are planned to assess the utilization of CSM and SFM at different phases of poultry growth, determine the optimum level of inclusion of CSM and SFM, and to measure the response of CSM/SFM and poultry to test enzymes, so as  part of the important of this study poultry industry supporters and providers including farmers, commercial producers and sellers, and nutritionists and feed manufacturers would benefit from the findings of this study, beside that the digestibility, absorbability and optimum rate of inclusion of CSM and SFM will be seriously investigated in order to efficiently established the use of CSM and SFM as alternatives for soybean.

Availability of ingredients, low prices, choosing appropriate feed processing techniques and developing suitable methods to eliminate or treat constraints of using plant origin proteins for poultry feeds are very important elements for high quality with low cost chicken meat production to meet an emerging trends for producers as well as high demand of consumers  (Jackson et al 1982; Hussain et al. 2011b), accordingly one of the expected results of current study is to help on reducing the cost of poultry feeds and poultry meats.

2.6. Conclusion.

After all these reviews of previous studies, we can conclude that  a considerable further researches required concerning constraints to use of alternative vegetable protein sources specially cottonseed and sunflower meals in diet formulation for poultry. In order  to decrease and remove limitations of its using and improve their digestibility for poultry, adopting applied techniques and strategies to raise quality of all alternative vegetable protein and  eliminate their high inclusion problems for economic poultry production, will help to incorporate these important ingredients safely  in the practical diets of poultry.

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