الفهرس 
Introduction.Only 14 pages are availabe for public view
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Abstract
One of the most crucial elements influencing poultry productivity is dietary protein. The knowledge of feeding amino acids has advanced during the last two to three decades. Undoubtedly, the creation of synthetic amino acids is responsible for this advancement. According to research by (Oviedo et al. 2021) dietary amino acids levels have been demonstrated to boost body weight and breast growth linearly while decreasing the accumulation of abdominal fat. Crude protein feed reduction with the use of amino acids appears to be the most successful nutritional strategy for reducing the global warming potential and nitrogen emissions associated with broiler production, without negatively affecting growth performance (Gonzalo and Lambert. 2022).
Increasing in amino acids and a rise in nitrogen excretion are caused by high crude protein levels in chicken feed. Crystalline amino acids are added to low crude protein (LCP) of broiler diets to supports the needs of developing tissues, nitrogen retention efficiency can be increased.
According to Bregendahl et al., (2002) some of the key reasons for using amino acids in lowering crude protein, feed intake (FI), and environmental pollution through reducing the excretion of pollutants (ammonia nitrogen) by farm animals. On the other hand, increasing metabolizable feed energy (ME) causes a considerable rise in body weight gain, a decrease in FI and an improvement in FCR according to ( Zaman et al., 2008, Nogueira et al., 2013) note that increasing feed intake has a negative impact on the feed conversion ratio (FCR) whereas decreases in CP and ME feed content cause weight gain (WG) (Kamran et al., 2008a).
According to Adela et al. (2013) the chicken feed low CP and ME, which has a big impact on how productively the animals operate. Energy is referred to as the driving force behind both the construction of the chickens’ bodies as they gain weight and their consumption of feed. Consequently, when determining the composition of feed, the degree of dietary energy is typically a basic starting point (Rajendran et al., 2015).
However, numerous recently published studies on broilers demonstrate that growth performance is unaffected by lowering dietary CP when compounded with an adequate supply of dietary AA (Belloir et al., 2017 and Van Harn et al., 2019).
A according to Hada et al. (2013), the levels of CP and ME in the diet had no impact on the metabolism of carbohydrates in broiler chickens. This might be as a result of the same birds’ careful management of carbohydrate metabolism to maintain blood glucose levels. Pathological and physiological factors, including age and species, may have an impact on blood components (Szabó et al., 2005).
The ideal amino acid ratio plays a crucial role in formulating low protein and energy diets for broilers. It ensures that the birds receive adequate and balanced amino acids, despite the reduced overall protein content in the diet. This approach optimizes growth performance, feed efficiency, and overall health of the broilers while minimizing the environmental impact associated with excess nitrogen excretion.
In low protein and energy broiler diets, the total protein level is reduced to meet the specific nutrient requirements of the birds while maintaining optimal growth rates. This reduction is achieved by utilizing highly digestible protein sources and incorporating synthetic amino acids to compensate for the lower protein content. The ideal amino acid ratio refers to the balanced proportions of essential amino acids provided in the diet.
Methionine, it was one of the most significant amino acids used in this investigation. Methionine is a sulfur-containing amino acid that is a part of all proteins. Since it is the first amino acid in every protein, it is necessary for protein synthesis and, consequently, for the body to carry out crucial functions. This is the initial stage in the construction of proteins, and it is connected to the transcriptional acid (TRNA) in the ribonucleic acid (TRNA) (MRNA). By raising methionine levels, breast meat output was improved (P<0.05) (Fariborz and Hasan., 2006).
Lysine, Most scientists use lysine as the foundation to which all other amino acids are tied when creating a ”optimal balance” because it is the second limiting amino acid in a diet based on corn and soybeans, after methionine. Chickens’ antibody response and cell-mediated immunity are decreased by insufficient Lys availability (Samadi and Liebert, 2007).
Threonine is a nutritionally essential amino acid supplement because poultry cannot produce it on their own. In commercial broilers, the dietary CP can be lowered by 1.5% units without impacting BWG and FI and by 0.75% unit without influencing feed conversion ratio (Manegar et al., 2017) L-threonine supplementation improves bird performance, and commercial broiler diets can reduce dietary crude protein by 1% unit without sacrificing quality of the bird performance (Ahmed, 2014).
Tryptophan, third-limiting amino acid in diets based on corn and soybean meal is Trp. Tryptophan is regarded as an essential amino acid due to its similar involvement in protein biosynthesis to that of other amino acids as well as the fact that Trp metabolism produces important chemicals including serotonin, melatonin, kynurenic acid, and quinolinic acid (Le Floc’h et al., 2011). Trp plays a role in the control of the hormones insulin-like growth factor 1, cortisol and corticosterone as well as the release of heat shock protein (Bello et al., 2018).
Valine, the amino acid is typically regarded as the next limiting one in broiler diet. In fact, the order in which amino acids become limiting in diets might vary depending on the amino acid composition of protein in various feedstuffs. (Abdallah et al., 2017) found that the optimal Val/Lys ratio for the starter, grower, and finisher periods was 500 mg/kg diet for broilers given LPD supplemented with significant quantities of methionine, lysine, and threonine. Furthermore, it improved the broiler’s growth performance and economic efficiency.
In light of all these observations, three points with different interests appear,
(1) The imperative necessity to preserve optimal/economical poultry productivity,
(2) The need to maintain preferred (from the consumer’s point of view) carcass traits and composition,
(3) The compelling need to maintain lower N excretion in order to environmental protection.
The present study was aimed to evaluate the reduced dietary crude protein and metabolizable energy levels with or without supplemental amino acids on growth performance, carcass characteristics and some blood measurements of Arbor Acres broiler chickens.