Poultry Nutrition

Poultry nutrition has been extensively researched so the nutritive requirement of laying hens is well known. The degree of sophistication is such that different strains of laying hens have feeds formulated to meet their specific requirements. The basic requirements are for protein, carbohydrates, fats, vitamins, and minerals. The protein requirement is met by including soybean meal, corn gluten meal, meat and bone meal, low-fat fish meal, and other protein rich ingredients. Carbohydrates are supplied by cereal grains most readily available in the locality. The fat content of laying rations is usually limited to the oils in the cereal grains. For some niche markets, low levels of omega-3-rich fish oils are included in the laying hens diet to produce omega-3 enriched eggs. In all laying hen rations a significant amount of minerals is needed, especially calcium to meet the needs of the hen in forming egg shells. The rations are also supplemented with premixes containing vitamins and trace minerals.  An important consideration in layer feed formulation is the availability of nutrients from different ingredients. Methionine is included in the formulations listed as it is the limiting amino acid in soybean meal. Often, with very small flocks allowed an outside range area, a much less complete diet is supplied in the feed. Such hens obtain a number of nutrients from insects, green plants, and the soil.

Enzymes in Poultry Nutrition

The use of exogenous enzymes in poultry nutrition is by far the most developed and established commercial application of enzymes in animal feed supplementation. It has evolved over the past 30 years or more. Today, the market for poultry enzymes is large, spanning nearly all the countries of the world. And as nations reduce the use of prophylactic antibiotics in poultry and farm animal nutrition, the role of enzyme supplements in poultry is likely to increase even further. Use of enzymes in poultry feed like other nutritional enzymes is driven by the fact of feed containing ingredients that the poultry are unable to digest or that impede digestive enzymes (Khattak et al., 2006; Café et al., 2002; Abudabos, 2010; Awati, 2014).

Large portions of commercial poultry feed contain barley, oats, peas, or wheat (feed ingredients capable of causing increase in digesta viscosity) and spent grains as energy sources as well as a vegetable protein source, commonly soybean meal. Today a range of other agricultural wastes, by-products, and coproducts are used in feed formulation for poultry particularly as the price of grain rises in response to feed–food competition. These can all contribute to the need for more enzyme supplementation as these unconventional feed ingredients are likely to have disproportionate amounts of components that are either not readily digested by the birds or are capable of interfering with the digestive process (El-Boushy and van der Poel, 2001; Choct et al., 2010; Coope and Weber, 2012). A range of enzymes have found commercial application in poultry intended to aid reduction in digesta viscosity and also to reduce the effect of antinutrients in the feed. Use of enzyme additives in poultry can be particularly important in young chicks with limited capacity to produce endogenous enzymes. Enzymes that have been commercially applied in poultry nutrition include enzymes of the cellulose complex and hemi cellulases as well as amylases and phytate (Ghazi et al., 1997a,b; Cowieson and Adeola, 2005; Cowieson et al., 2006a,b; Cowieson and Ravindra, 2008; Centeno et al., 2006; Cowieson, 2010; Du Plessis and van Resenburg, 2014). To lesser extents, lipases and proteases have also been employed in poultry but mostly as part of constituents of feed enzyme complex.

Minerals In Poultry Nutrition

Micro minerals have long been known for their influence on the growth performance, metabolism, and immunity of poultry flocks. For instance, zinc (Zn) and copper (Cu) are acknowledged being important modulators of the mechanisms against infections, due to the antimicrobial effects, inflammation, and oxidative stress. Trace minerals supplementation is not new in poultry nutrition, but higher levels may be supplemented to maximize performance. On the other hand, concerns related to the increased excretion of these minerals into the environment are driving the industry to use more bioavailable sources of minerals, such as organic minerals, which would reduce the concentration of minerals added into the feed.

Zinc is an essential micromineral required for many biological functions, including growth, reproduction, meat quality, and immune response against pathogens [168]. The dynamic distribution of Zn in the body of chickens changes during infections. As shown by Bortoluzzi et al. [169], the concentration of Zn in the serum decreased and increased in the liver 7 days after challenge with Eimeria maxima. Additionally, Zn concentration in the serum slightly increased in birds supplemented with 90 mg/kg of ZnSO4 compared to no supplemented birds. Indeed, severity of growth depression has been observed to be lessened when supplemental Zn was increased to 85–90 mg Zn/kg diet [170,171]. Additionally, organic Zn induced higher expression of A20, an anti-inflammatory regulator, down regulated the expression of inflammatory inducers, including NF-kB p65 [172,173], and promoted MUC2 and IgA production, when compared to its inorganic counterpart [172]. Epigenetic mechanisms alter gene expression without changes in DNA sequence and can explain the effects of Zn on the cell. It has also been demonstrated that organic Zn had a significant impact in lessening the inflammatory response in the intestine by down regulating the expression of pro-inflammatory cytokines, such as IL-8 and IFN-γ, TLR-2 and iNOS [169,174].

Copper is also an essential trace element in animals for exercising several important roles. The poultry industry has used prophylactic concentrations of dietary Cu for its ability to improve feed efficiency for a long time. One of the first reports of Cu supplementation having a growth-promoting effect was that of Mehring et al. [175], suggesting an effect similar to that of the antibiotics. High concentrations of Cu were originally thought to having benefits in prevention of crop mycosis, but addition of up to 250 mg of Cu/kg of diet results in increased erosion to the lining of the gizzard [176,177] and an “inhibition of normal fermentation” in the ceca of the chick [177]. A more recent study [178] has reported that high dietary supplementation of Cu (up to 330 mg/kg) led to reduced antioxidant capacity and higher oxidative stress in chickens. Additionally, it was shown that the excess of dietary Cu upregulated the mRNA levels of TNF-α, IFN-γ, IL-1, IL-1β, IL-2, iNOS, COX-2 and the concentrations of TNF-α, IL-1, IL-1β and the protein expression levels of TNF-α and IFN-γ in the spleen, thymus, and bursa of Fabricius. This suggests that excessive Cu can induce inflammatory responses and provides evidence of Cu toxicity mechanisms in broiler chickens [178]. On the other hand, lower dietary supplementation of Cu (20 mg/kg) reduced cholesterol and triglycerides, increased IL-6, IgA, and IgY, and the glutathione peroxidase activity in the serum of broilers. These results show that low dietary supplementation plays an important role in blood lipids, and immune and antioxidant defenses in chickens [179].

Manganese (Mn) is described as a trace mineral associated with better immunity, or to functions that support immunity [180], such as the synthesis of muco polysaccharides through its activation of glycosyl transferase [181]. It has been reported in broiler chickens that on day 6 post challenge with Eimeria acervulina there was a reduction of Mn absorption by 23% and 34% in two consecutive studies, respectively [182]; however, there was an increase in Mn absorption compared to uninfected control birds by day 10 after challenge, and then it returned to normal rates as the unchallenged birds. Although there is a lack of studies relating Mn supplementation and its different presentation forms on the immune response against enteric diseases in poultry, one can assume that Mn is beneficial during enteric challenges due to its role in the production of muco polysaccharides. Burin Junior et al. [183] have shown that birds fed organic Mn had a more efficient response against a S. Enteritidis vaccine when compared to birds fed its inorganic counterpart. Zhang et al. [184] found that the supplementation of 50 or 100 mg/kg of Mn to broilers under S. Typhimurium reduced the intestinal permeability caused by the challenge. Unlike the effects observed in Salmonella-treated birds, serum inflammatory cytokines IL-1, IL-6, and TNF-α were not altered by Mn itself. The authors speculate that dietary Mn promotes inflammatory response in the spleen that plays an important role for the fight against S. Typhimurium challenge for broilers [184].

Anti-nutritional Factors In Poultry Nutrition

Phytic acid, NSPs, tannins, lectins and enzyme inhibitors (like trypsin, chymo trypsin and α-amylase inhibitors) in plant materials are considered ANFs in pig and poultry nutrition. However, except for NSPs, all of other mentioned ANFs are heat-labile and reduced/eliminated by the common hydrothermal processes, especially more intensive ones like expander processing and extrusion (Goodarzi Boroojeni et al., 2016). The consequence of this reduction is higher availability and digestibility of nutrients for pigs and poultry. The impact of HTP on the fiber/NSPs fraction of feed can also be considered as destructive, while this destruction is often physical and without degradation of the polymers (De Vries et al., 2012). The consequences of this destruction are different for fiber digestibility compared with digestibility of other nutrients in feed. Destruction of the physical fiber conformation by HTP improves its digestibility in pig and poultry but can, through increasing in NSPs solubility and digesta viscosity, impair digestion and absorption of nutrients in the digestive tract of pig and poultry (De Vries et al., 2012; Goodarzi Boroojeni et al., 2016). Destruction of the fiber fraction and increase in fiber solubility could be more pronounced when expander processing or extrusion are applied compared with pelleting processes (Wolf, 2010; De Vries et al., 2012). However, it should be noted that various NSPs display a different susceptibility to solubilization by mechanical or hydrothermal processing. For instance, β-glucans in barley and pea could be more easily solubilized than arabinoxylans from secondary cell wall tissue in oat, barley hulls and wheat bran (De Vries et al., 2012). Therefore, pelleting or even grinding of feed ingredients containing easy-solubilized NSPs can lead to an increase in solubility of the fiber fraction (Ralet et al., 1990; Anguita et al., 2006).