The poultry industry has emerged as the fastest growing segment of the livestock sector both globally and in India. In broiler farming feed cost alone accounts to more than 70 percent of the expenditure on chicken rearing and therefore net returns from broiler production are greatly dependent on the quantity and quality of the feed offered to broilers. Source of protein being the costliest dietary ingredient, attempts are therefore being made by research workers by altering crude protein content of broiler diet without affecting the performance.
In India, mostly the protein levels recommended by the Bureau of Indian Standard (2007) are taken as a guideline in providing nutrient requirements for flocks. However, modern broilers consume less feed per unit body weight gain and reach their target weights in fewer days due to genetic improvements compared to broilers used before (Dozier et al., 2008). This necessitates that the dietary amino acids need of the modern commercial broiler should be increased to cope up with the increased rate of growth. It has been recognized that, poultry actually require a specific quantity and balance of the dietary essential amino acids and sufficient nitrogen for synthesis of the non-essential amino acids, rather than merely crude protein content (Abudabos and Aljumaah, 2012). Therefore, fulfilling dietary amino acid needs for optimum growth and meat yield has been recognized to be of utmost importance in broiler nutrition (Dozier et al., 2008). Thus, with reduction in the level of CP of the ration, it is possible to achieve significant cost savings (Dozier et al., 2008). Formulating broiler feed with lower CP and with supplementation of limiting essential amino acids could be one of the possible approaches to reduce feed cost without compromising the performance of the broilers.
Methionine, lysine and threonine are the first three limiting amino acids in corn-soya based diet (Ayasan et al., 2009). Lysine is used as the reference to which all the other indispensable amino acids are rationed to achieve an ideal protein pattern. Almost all of the lysine in the diet is used for protein accretion and that is the reason, why it is considered as a reference amino acid.
Lysine not only increases protein synthesis but also decreases protein catabolism (Kidd and Fancher, 2001). Lysine content in breast muscle is relatively higher than other amino acids and represents approximately 7 per cent of the protein in breast meat. Breast muscle provides the greatest portion of edible meat in broilers and the contribution of breast muscle to total of carcass meat is approximately 30 per cent of total carcass meat and contributes close to 50 per cent of total edible carcass protein and also help in improve FCR if supplemented above requirement.
Methionine acts as a lipotropic agent through its role as an amino acid in balancing protein or through its role as a methyl donor and involvement in choline, betaine, folic acid, and vitamin B12 metabolism. Methionine supplementation over and above requirement increases body weight gain and FCR in broiler chicken.
Threonine participates in protein synthesis and its catabolism generates many products important in metabolism (i.e. glycine, acetyl-CoA and pyruvate). It serves as a component of body protein and precursor of glycine and serine which are involved in immune responses, needed in gastrointestinal mucin production.
Supplementation of synthetic amino acids to diet is important not only on nutritional and economic aspects, but also on environmental aspects by decreasing nitrogen excretion from poultry which results in decreased ammonia production in the shed. Reduction in protein level in broiler diet can also allow for the use of a greater variety of feed stuffs which can be valuable in it as a method to increase flexibility in the choice of locally available feed stuffs.
Now a days it has been emphasized that, poultry feed should be formulated in such a way so as to produce the most economical finished product, rather than trying to meet the rigid set of feed specification. The formulation of protein and amino acid-balanced diets for broiler chickens without synthetic amino acid supplementation has limitations because of relatively high requirements of amino acids and as such synthetic amino acid supplementation has become an interesting part of the formulation.
The most economical crude protein and amino acid levels in feed may not necessarily be the levels that contain the required amino acid levels for maximum growth or minimum carcass fat but the diets providing the largest difference between costs and returns. It is also necessary to observe whether supplementation of low protein broiler diet with synthetic source of methionine, lysine and threonine as first, second and third limiting amino acids can give better profit without compromising broiler performance.
It has been found that the amino acid supplementation to birds with low protein diet will help to increase body weight by utilizing nutrient efficiently due to availability of extra amino acids for anabolism. Moreover, adding the essential amino acids such as lysine, methionine and threonine to the 7.5 per cent low crude protein diets will improve the cumulative FCR and can overcome the adverse effects of the low crude protein levels in the diets. It is due to better availability and balance of limiting amino acid that trigger the efficiency of protein utilization for body weight gain.
Low protein (7.5%) diet is responsible for the deposition of abdominal fat per cent while supplementation with synthetic amino acids decreases the deposition of abdominal fat. The higher level of abdominal fat because of decreased dietary protein widened the calorie protein ratio resulting in to higher energy intake relative to protein intake. This increased energy intake will be diverted towards fat synthesis and its deposition in abdominal area, and this effect can be overcomes by supplementation of amino acid above the given standard when protein level is decreased in broiler chicken.
The reduction of crude protein content of broiler feed along with extra provision of the lysine, methionine and threonine will not affect live body weight, feed conversion ratio, dressing percentage, breast meat percentage and net profit per kg live body weight. Further research is needed to unveil the many more facts regarding supplementation specific limiting amino acids to broilers.
Abudabos, A. and R. Aljumaah (2012) Broiler responses to reduced protein and energy diets supplemented with lysine, methionine and threonine. J. Poult. Sci. (49) : 101-105.
Aletor V. A., II. Hamid, E. Niess and E. Pfeffer (2000) Low-protein amino acid supplemented diets in broiler chickens: effects on performance, carcass characteristics, whole-body composition and efficiencies of nutrient utilization. J. Sci Food Agric. 80: 547-554.
Awad E. A., M. Fadlullah, I. Zulkifli, A. S. Farjam and L. T. Chwen (2014) Amino acids fortification of low-protein diet for broilers under tropical climate: ideal essential amino acids profile. Ital. J. Anim. Sci. 13: 270-274.
Daghir, N. J. (1983) Effect of lysine and methionine supplementation of low protein roaster diets fed after six weeks of age. Poult. Sci. 62 (8): 1572-1575.
B.I.S. (2007) Bureau of Indian Standards, Poultry Feeds. Specification (Fifth Revision). IS: 1374-2007, Manak Bhavan, 9, Bahadurshah Zafar Marg, New Delhi-11 110002.
Khan S. A., N. Ujjan, G. Ahmed, M. I. Rind, S. A. Fazlani, S .Faraz, S. Ahmed and M. Asif (2011) Effect of low protein diet supplemented with or without amino acids on the production of broiler. African J. of Biotech. 10(49): 10058-10065.
Waldroup P.W., Q. Jiang and C. A. Fritts (2005) Effects of supplementing broiler diets low in crude protein with essential and nonessential amino acids. Int. J. Poult. Sci. 4(6): 425-431.