**4.5 Use of feed additives**

Feed additives are employed in poultry diets in order to improve digestive efficiency. As a consequence, poultry productivity is enhanced. Nutritional advances in feed additives include enzymes, synthetic amino acids, commercial preparations of vitamins/trace minerals, probiotics, prebiotics and toxin binders among others.

Feed enzymes are commercial enzyme products aimed at augmenting the endogenous enzymes secreted in the gut of birds when fed in the diet so as to improve availability of nutrients. Researches on enzyme usage is necessitated by wide use of vegetable proteins (e.g. legumes and oilseed meals) and some cereal grains in poultry diets.

The use of vegetable proteins was in response to a total ban on the use of animal protein sources in feeds by the European Union [31]; which hitherto was the main protein source in poultry diets due to their high digestibility. However, these vegetable proteins are characterised by high levels of anti-nutritional factors such as indigestible non-starch polysaccharides, phytic acid, tannins and alkaloids; which affect utilisation of nutrients.

Besides, some feed grains such as wheat, barley, sorghum and rye contain appreciable amounts of soluble non-starch polysaccharides that can cause very viscous gut content. Hence, the advances made in feed enzyme research culminated in the use of feed enzymes to depolymerise the soluble and insoluble pectic polysaccharides [32, 33] as well as hydrolyse phytates [34] in diets containing high levels of vegetable proteins and some cereal grains. In fact, feed enzymes prevent severe imbalances of nutrients that can remain undigested and reach the large intestine; thereby creating favourable environment for pathogens and consequent disease conditions. A good number of studies involving enzymes in poultry nutrition has

been reviewed which have demonstrated improvements in feed utilisation with enzyme supplementation [35–37].

Additional beneficial effects of feed enzymes, particularly phytase, in cereal and oilseed- based diets include the following: release of digestible phosphorus to reduce the use of expensive supplemental inorganic phosphorus (e.g. dicalcium phosphate); release of minerals such as calcium, magnesium, zinc and potassium which are complexed with the phytate molecule; and prevent excessive excretion of phosphorus in manure into the environment [34].

The bird's gut microbial ecology has implications for feed digestion and disease control. This has to do with maintenance of natural balance of beneficial and pathogenic microorganism populations in the gut. Thus, the use of antibiotics previously as feed additive tended to cause imbalance between these two groups of microbes by eliminating largely the beneficial microbes as well as cause meat contamination and resistance problems in humans [38, 39]. Hence, the introduction of probiotics/ prebiotics/synbiotics (combination of pro-prebiotic) as replacement for antibiotics.

Probiotics are a culture of live microorganisms. The probiotic product may contain microbes such as *Aspergillus oryzae, Lactobacillus acidophilus, L. bulgaricus, L. planetarium, Bifidobacterium bifidium, Streptococcus lactis and Saccharomyces cerevisiae*. Some of the commercially available probiotics for poultry are Bactocell®, BioPlus 2B®, Cylactin®, Lactobacillus acidophilus D2/CSL®, Microfern®, Oralin®, Protexin® and Thepax®. These products promote growth of beneficial microbes which competitively exclude the pathogenic microbes [40] and may as well secrete enzymes which aid digestion of feed.

The use of prebiotics in animal nutrition post- dated probiotics with favourable effects on poultry health and meat quality [41, 42]. It has been defined recently as "a non-digestible compound that, through its metabolization by microorganisms in the gut, modulates composition and/or activity of the gut microbiota, thus conferring a beneficial physiological effect on the host' [43]. Commonly used prebiotics are mannanoligosaccharides (MOS), fructooligosaccharides and inulin. Generally, prebiotic products are resistant to attack by endogenous enzymes and therefore reach the site for proliferation of gut microorganisms, where they interfere with colonisation of the pathogenic microbes and thereby exclude them [44].

Inclusion of synthetic essential amino acids in poultry has been on the rise as a result of improving efficiency of protein utilisation. This is in line with current trend of formulating diets based on digestible amino acids in order to reduce amount of dietary protein [45]. These are DL-Methionine, L-lysine HCl, L-Threonine and L-Tryptophan. Initially, the idea was to meet first-limiting amino acids (Lysine and Methionine) requirements for poultry; however, with the need to further reduce dietary protein requirements as well as reduction in nitrogen excretion, this calls for increased use of second and third limiting amino acids such as L-Threonine and L-Tryptophan as well as the next limiting amino acids including Isoleucine, Valine and Arginine [45–48].

Advances in dietary supplementation with vitamins (water/fat soluble) and trace minerals (Zn, Cu, Mn, Se, Co, Fe) continue to be made and have brought about improvements in feed utilisation, growth performance and welfare of birds [49]. Vitamins and trace mineral supplements are vital feed additives aimed at supplying sufficient amounts that meets the needs of the biochemical systems of the cells of birds culminating in varied benefits. These benefits include enhanced mineral uptake, improved immune system, proper tissue and bone development, cellular growth as well as amelioration of oxidative stress in birds [49].

The use of toxin binders in poultry feeds has counteracted problems of mycotoxins associated with cereal grains [50, 51].

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*Advances in Poultry Nutrition Research-A Review DOI: http://dx.doi.org/10.5772/intechopen.95990*

pathogens, quality of meat and eggs in birds [52, 53].

The use of nano-minerals in poultry nutrition is a recent concept that is gaining

Several researches have highlighted the problems of metal toxicity in poultry; which led to the establishment of nutritional guidelines on safety levels to protect both birds and humans from metal toxicity [54]. Nutritionally beneficial ones for good health but whose dietary excesses create health problems include iron, copper, manganese, zinc, etc.; whereas poisonous ones which may contaminate feeds from the environment include arsenic, mercury, lead, cadmium, vanadium, etc. [55, 56].

Studies on dietary modification have played a major part in the production of nutritionally-improved eggs referred to as "Designer Eggs". By way of nutritional manipulations of the cholesterol content and its fractions, lipid profile, fatty acids, amino acids and minerals can be modified to produce healthy eggs for humans [57]. This can also be done through addition of therapeutic pharmaceutical compounds [57].

**4.9 Nutritional management, gastro-intestinal tract conditioning and poultry** 

through nutrition if and only if the health status of birds is not compromised. Therefore, current nutritional researches are geared towards optimising poultry health and consequently their welfare. Some of these nutritional strategies with positive impact on poultry welfare have been reviewed extensively [58]. They include: manipulation of diet composition (e.g. dietary ME/CP as a way of controlling the body composition to prevent body fatness of market broilers or fatty liver haemorrhagic syndrome in layers); addition of essential fatty acids such as linoleic acid and linolenic acid to prevent lesions or supplemental fats/oils to increase dietary ME values; use of calcium and phosphorus (an approximate ratio of 2: 1), or vitamin D to prevent bone problems such rickets and tibial dyschondroplasia or cartilage abnormalities that can lead to welfare problems such as osteomyelitis and femoral head necrosis; use of major supplemental mineral like sodium/vitamin and trace mineral supplements to boost normal health and/or under adverse conditions; use of feed additives such as enzymes and probiotics discussed above (Section 4.5) to improve feed efficiency with added advantage of less sticky excreta (better litter quality with less incidence of hock burns) and control of disease causing organisms, respectively; dietary modifications to help birds cope with stress, particularly under hot climatic conditions (e.g. decreasing crude protein content, use of synthetic amino acids to increase amino acid intake, use of fat to help decrease heat increment, use of sodium supplement as bicarbonate for maintenance of blood electrolyte balance, use of vitamins such as vitamins C, E and A to help in heat and other types of stress); and physical manipulation of feed such as mash feeding and feed restriction to control growth for maintenance of good health (e.g. lower mortality, reduction in metabolic disorders, improved walking ability).

It's undeniable fact that achievement of productive efficiency can only be attained

grounds as a result of varied application of nanotechnology in animal production systems. This has to do with alteration of particle size to few nano meters (1–100 nm) and studies reviewed so far have proved that feeding of nanoparticle improved digestive efficiency, immunity, growth rate, performance, resistance to

**4.6 Use of nano-minerals**

**4.7 Combating metal toxicity**

**4.8 Production of designer eggs**

**health**
