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Amino acids are important components of poultry diets. Amino acids play an important role in structural and protective tissues in the body and are also important in enzyme and tissue functions (NRC, 1994). Deficiencies can cause detrimental effects on growth and production. Now a days Nutritionists taking interest in formulating diets on digestible amino acids basis. Dietary amino acids effects on feed intake, intestinal physiology, immunity, meat quality and also as anti-oxidants.
Nutritional requirements of essential amino acids and the nutritional composition of raw material is essential for the balancing of diets in broiler and layer. Poultry diet is supplemented with synthetic amino acids to enhance the production.
Supplementation of Methionine and Lysine in poultry diets is very essential for improving the utilization of protein. Now a days, for the formulation of poultry diets, more attention has been given to the ideal amino acid profile by the nutritionists.Previously, diet formulation to poultry requirements were aimed to get maximum production without special concern for nutrient over supply, especially protein and amino acids.
Recent environment constraints have forced Nutritionists to base amino acids levels because Nitrogen retained in animal products and also excreted in feacal material.
A lot of studies describe the importance of amino acids supplementation as follows:1) reducing cost in production,2) producing the optimal balance of essential amino acids that enhances the growth, maximizes edible meat yield, reduces carcass fat and enable precise selection of progeny for breeding programs.
Lysine, Methionine and Threonine are limiting amino acids which are very essential for broiler and layer.
According to NRC by increasing Lysine in starter or grower finisher diets increased both performance and mortality.Methionine is also classified into limiting amino acid because it is limited in plant protein sources. This amino acid is essential for protein synthesis,
methyl donor group for normal cellular metabolism and for normal formation of co-enzyme. It is also a precursor of important intermediates in metabolic pathway such as cystine or cornitine.Threonine is also play important role in poultry by increasing F.C.R annd healing of wounds. Amino acids are derived from fermentation processes, DL-methionine (DLM) is produced from a complex chemical synthetic process, and the starting material for its production is a acrolein (a 3-carbon aldehyde).
Normally, amino acids, including methionine, are mainly absorbed through the small intestine.
Amino acids and feed intake:
Lot of studies have demonstrated that mild deficiencies of amino acids (Lysine and Threionine) in broiler (Ferguson and Gous,1997),Methionine in layers(Picard et al.,1997) lead to small increase in intake and animals adapt very quickly (days in layers) to such limited content variations.
However, deficiencies in essential amino acids, particularly Tryptophan for broiler (Henry et al, 1992) and Methionine for broiler and layers strongly affect feed intakle.
Formulating feeds based on amino acids have advantages over formulating on a total amino acids basis by describing more accurately their potentialnutritional value (Fernandaz et al., 1995).
Feeds formulated on the basis of available amino acids more closely reflect the actual amino acids requirements.
According to Baker et al(2002), the complexity to establish accurate ratios for amino acids lies in the possibilities of response variables to be utilized(such as weight gain and feed coversion).
Few studies that have addressed digestible amino acid requirements of poultry that have covered the full productive life of commercial toms (Firman and Boiling; 1998, Baker et al., 2003). Formulating diets on a digestible amino acid basis has the potential to reduce feed cost through a reduction in total dietary protein thus enabling greater flexibility in the feed formulation ingredient matrix (Baker et al., 2003).
Amino acids and intestinal physiology:
According to (Nichols and Bertolo,2008) Threonine is very important for G.I.T functioning.One of the primary fate of this amino acid is synthesis of intestinal proteins (mucins) which are mainly secreted into the lumen as mucus which protect the gut from pathogens and antinutrional factors.
All environmental factors impacting the gut integrity might thus impact the need for Threonine.Intestinal inflammation by increasing the mobilization of endogenous protein appears to reinforce the demond for Threonine.moreover, using different environmental conditions such as a clean and a dietry litter. It has been demonstrated that cobb birds in the dirty conditions responded better to the Threonine supplementation than birds in clean environment (Kidd and Corzo, 2006).
However, a mild coccidial challenge which might slightly affect the intestinal mucosa did not require further Threonine supplementation (Kidd et al., 2003).
Competition for essential nutrients such as amino acids between native microflora and pathogens may also be a limiting factor in gut colonization by pathogenic microorganisms. Amino acids such as Serine, Asparine and Arginine have been suggested to inhibit invading microorganisms (Usnijima and Seto, .1991).
Amino acids and immunity:
Recently, more fundamental research have been undertaken to better understand the relationship between amino acids and immune function.Amino acids might indeed regulate activation of T-Lymphocytes,B-Lymphocytes,Natural killer cells and Macrophages,improve cellular redox status,lymphocyte proliferation,as well as production of antibodies and cytokines.
Dietary supplementation with Methionine and Cysteine has indeed been proven beneficial for the immune system in chickens infected with Newcastle virus through T-cell proliferation, IgG secretion, leucocyte migration and antibody titer (Tsiagbe et al., 1987).
Using purified diet, methionine need appeared higher for growth than for humoral immunity (Bhargava et al., 1971).
Supplementary Methionine, but not choline, optimized the response to phyto-hemagglutinin as well as total antibody response to SRBC a T-dependent antigen (Tsiagbe et el., 1981).
The Methionine level to optimize leukocyte migaration inhibition assay was also higher than the level to improve growth in broiler chicks (Kidd, 2004).
Lysine ,one the key amino acid for protein synthesis and muscle deposition has also been demonstrated to be involved in the synthesis of cylokines,proliferation of Lymphocytes and thus in the optimum functioning of immune system in response to infection (Konahi et al.,2004).
An inadequate supply of Lysine would reduce antibody response and cell-mediated immunity in chicks (Chen et al., 2003).
The role of Arginine in immune function has recently been required by Kidd (2004).
The immunomodulatory action of Arginine is mainly mediated through cellular immune response rather than humoral ones (Jahaniah., 2009).
Threonine is also a major component of plasa gema-globulin in animals.Dietary Threonine intake also influence components of immune system (Review Li et al., 2007).
Role of amino acids in immune responses :
Stimulation of lymphocyte proliferation,
enhancement of antibody production
Signaling molecule; killing of pathogens;
regulation of cell metabolism and cytokine
Neurotransmitter; inhibition of T-cells and
Glutamine Glu, Asp
Upregulation of immune cell metabolism and function
Neurotransmitters; cell metabolism
Ceramide and phosphatidylserine formation
Allergic reaction; vasodilator; gastric acid & central
Inhibition inflammation, enhancement specific
Regulation of NO synthesis; antiviral activity; ketogenesis
Oxidant; inhibitor of NO synthesis
Synthesis of bioactive substances regulating neuronal
function and cell metabolism
Killing pathogens; intestinal integrity; a signaling
Antioxidant; neurotransmitter; immunomodulator
Synthesis of mucin protein intestinal integrity; immunity
Neurotransmitter; inhibition of inflammation
Bio-rhythms; free radical scavenger; antioxidant
Inhibiting production of proinflammatory cytokines; enhancing immunity
EPN, NEPN Melanin
Neurotransmitter; control of behaviour, immune response
Neurotransmitters; glycogen and energy metabolism
Free radical scavenger; inhibition of inflammation
Gene expression; DNA and protein synthesis; antioxidants; cell function, proliferation and differentiation
(Adopted from Kidd, 2004, Li et al., Niewold, 2008)
Amino acids as anti-oxidants:
Cellular antioxidant mechanisms are more often attributed to vitamins (e.g. Vitamin E and Vitamin C) than to amino acids. However, sulphur amino acids play a major role in antioxidant systems of the cell through various systems.
Methionine sulfoxide educates A and B (MSR-A and MSR-B) is an enzymatic system which turns back into methionine. Methionine is considered as the one main target of free radicals in protein and by the action of MSR A or B system reverse to methionine, it can be considered as a free radical scavenging system (Stadman et al., 2005).
Cysteine appears like a "conditional" limiting amino acid depending on the stress level or inflammatory step, methionine sources seems to give differential results on oxidative status. In different pro-oxidant conditions (e.g. protein level and heat stress) DL-HMTBA, which is more easily transformed into Cysteine and Taurine than DL-Methionine (Martin-Venegas et al., 2006), appears more effective to sustain antioxidant status of the cell, mainly by maintaining higher GSH/GSSG ratio (Swennen et al., 2010; Willemsen et al., 2010.
Tryptophan catabolism generates serotonin, melatonin and anthranilic acid (Li et al., 2007).
Amino Acids and Meat Quality:
It has been reported that the Amino acid supply can modify muscle growth .However, a recent report from Conde-Aguilera et al. (2010) showed that a deficient supply of Methionine in poultry affected the Amino acid composition of body proteins.
Meat quality also depends on rearing conditions that can be modulated by amino acid supply. Berri et al. (2008) showed the effect of high and low rearing density that significantly altered the drip loss of the meat during storage. In this study drip loss was significantly increased from 1.01 to 1.18% respectively with bird density changing from 13 to 26 birds per mÂ². Moreover, the increased of dietary lysine from 0.83 to 1.13% in finishing diet, allowed to decrease drip loss from 1.01 to 0.82% and from 1.18 to 0.91% respectively in low and high density groups. This effect was correlated with a higher ultimate pH value obtained with the high dietary lysine compared to low dietary supply.
Free Glutamate contributes to meat taste including 'delicious', 'umami' and 'brothy' tastes, and is one important taste-active component of meat. It was suggested that among chicken, pork, and beef, the meat including the most free Glu was chicken, followed by pork, and beef (Kato et al., 1989). Free glutamate (Glu) content in chicken meat was decreased by 10 or 35 days of restricted feeding (Fujimura et al., 1997, 2001). Chickens given adlibitam or restricted feeding exhibited different meat tastes, using sensory evaluation assays (Fujimura et al., 2001). Therefore, it became obvious that feed was one important factor of meat taste.
Amino acids have largely demonstrated effects beyond their roles of building blocks of the protein accretion: from a better gut functioning to an enhanced immune system. More research is necessary to determine the optimal requirements of amino acids to improve not only muscle development but also meat quality and stability.
Dietary supplementation beyond the quantity required for optimal growth and feed efficiency has often been demonstrated to improve homogeneity or reduce flock variability which has important economic impact at the slaughter plant level (Schutte et al., 1997; Leclercq et al. 1998; Corzo et al. 2004).
The results obtained from different studies implicate that excess lysine and methionine could improve immune system, decrease abdominal fat content and feed conversion ratio, increase breast muscle yield and carcass efficiency. So, it
is suggested that levels of lysine and methionine in excess of NRC (1994) recommendations may result in enhanced health and economical performance and processing yield.