Feed and water are essential for living animals. To meet the nutritional requirements of any breed of chicken, there is a need to be accurate of ration formulation for that breed of chicken. Different breeds of poultry have different nutrient requirements. In commercial production, for an example, diet specifications for broilers versus layers are deliberately differentiated (Chadd, 2007). The exploitation of chicken genes in a free stress environment, by giving chickens an adequate balance diet with essential nutrients resulted in improved growth performance to the highest genetically limit (Kingori et al., 2010).
Ration formulation is the process of quantifying the amount of ingredients that need to be combined to meet nutrient requirements of chickens. Therefore, the process of ration formulation requires an intimate knowledge of the chicken, its daily nutrient requirements, its physiological needs and a more comprehensive understanding of the ability of the selected feeds to provide the most desirable nutrients. The ingestion of the optimal level of dietary nutrients for parent stock, broilers, layers, indigenous or any other type of chickens is highly dependent on the level of feed intake (Chadd, 2007). The feed efficiency in layers is defined in terms of the kilograms of feed required to produce one kilogram of eggs. Genetic improvements in productivity continue to improve the use of resources such as feed and energy. The improved genetics lead to the need for enhanced digestible efficiency of amino acids and phosphorus (Besbes et al., 2007). The reproductive performance attributed to a modified body composition at the onset of lay can be highly associated to feed management during rearing (Van Emous et al., 2015).
2.5.1 Protein requirements
The specified protein requirements for a particular chicken genotype is very important to enhance its potential maximum performance. According to Van Emous et al. (2015),
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the differences in body composition at the end of rearing is often influenced by the level of protein intake. The effects of protein excesses on growth performance are due to the changes in the voluntary feed intake (Thu et al., 2009). Feeding animals below their protein requirement does not improve protein utilisation. Protein deficiency in feed reduces growth as a consequence of depressed appetite and, intake of nutrients (Kingori et al., 2003). Smith & Pesti, (1998) reported that the body weight increased at a decreased growth rate with an increase in protein level, and with a slight increase in the feed intake of the cross-broiler strain. Van Emous et al., (2015), proved that differences in body composition of pullets resulted from different levels of protein intake during rearing can disappear during laying period. However, Dairo et al., (2010) reported that an increase of dietary protein levels will reduce the total feed intake and improve final feed conversion ratio (FCR).
Economic evaluation on the decreasing CP levels from 23% to 20% resulted in reduced feed cost per kilogram of live body weight gain. The feeding of diets of varying dietary protein levels (17.72 – 21.52%) did not differ significantly on the effects of final live weight, feed intake, body weight gain, FCR and water intake of the broiler chickens (Folorunso & Onibi, 2012). Kamran et al., (2008), discovered that reducing dietary CP did not affect the growth performance of the chicken and it can be used to reduce feed cost with supplementation of relevant alternate feedstuffs are supplemented. However, different results were observed on layers, where the egg weight of hens fed high- protein diet was significantly greater than that of hens fed the low-protein diet during 97 and 98 weeks of age (Gunawardana, Roland & Bryant, 2009). Feeding the hens high level of protein did not result in an increased protein deposition, however, nitrogen excretion through the urine increased rapidly (Kingori et al., 2010).
The CP requirement for broilers differ during the different growth phases. The pre- starter fed from 0 to 10 days of age contains CP of 22.5%, starter fed from 11 to 21 days of age contains CP of 21.0% and grower fed from 22 to 42 days CP of 19.5% (Panda et al., 2014). The protein requirements for layers is lower than that of broilers.
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(Shim et al., 2013), formulated four diet treatments with three levels of protein and the outcome revealed that the increase in protein level, increased cost and returns.
2.5.2 Energy requirements
Energy is one of the most important components of food and therefore it generates a lot of interest and challenges to all animal nutritionists. Researchers in the field of nutrition are very determinants in the evaluation of the performance and production coefficients on farm animals (Dairo et al., 2010). Energy is produced when the feed is digested in the gut. Energy may be released as heat or it is trapped chemically and absorbed into the body for metabolic purpose. The wide range of dietary energy levels (2,684 to 2,992 kcal of ME/kg) was recorded (Yuan et al., 2009).
Dietary energy is continuously investigated in the poultry industry across the world because the increase of dietary energy has effects on general performance of the chickens. Wu et al. (2005) reported that when the diet with increased dietary energy levels resulted in linearly increased feed intake from 107.6 gram (g) to 101,1 g per hen per day. This resulted in a net increase of 6.5 g per hen per day or 6% of the overall feed intake. The egg production, egg weight and egg mass (in gram of egg per hen per day) was not affected by increased energy on diet by 7.5% (2,795 kcal ME/kg diet) compared to a control group at (2.600 kcal ME/kg diet) (Panda et al., 2012). Feed intake and egg weight can affect cost of production and profits. The energy and lysine ratio required for optimal profits varied with egg price and feed ingredient price, which were variable (Wu et al., 2005).
2.5.3 Lysine requirements
Lysine is regarded as the key amino acid for poultry whereby the concentrations of the other amino acids may be related to it. The maintenance requirements for the number of amino acids, including lysine and threonine, per adult rooster were determined by using a mathematical model (Leveille, Shapiro & Fisher, 1960). Lysine is one of the
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first and limiting amino acids found in corn-soybean meal diet for laying hens (Alagawany & Mahrose, 2014). The maintenance of amino acid requirements are often defined at nitrogen (N) equilibrium, the state in which N intake equals the sum of N losses where the N content of the body remains constant (Nonis & Gous, 2008). However, there is considerable research that directs towards defining the minimum intake of dietary CP and amino acids to reduce the nitrogen in the excreta in order to reduce nitrogen loss to the environment (Waguespack et al., 2009). The pullet body requirements changed rapidly during the growth stage and the amino acids had to be adjusted accordingly. After certain growth stage the body of pullet remain constant and requirement of amino acids can be perfectly matched (Sakomura et al., 2015). The limitation of non-essential amino acids, can result in limited protein synthesis and reduce egg production (Cristina et al., 2013).
Nonis & Gous (2008) reported that most authors approached the problem of estimating the amounts of amino acids required for maintenance using response trials with populations of laying hens or growing chickens. The developed ready model has been used to estimate the coefficients of response (amino acids (mg) required per egg output (g) per body weight (kg) daily) to amino acids intake in laying hens (Fisher, Morris & Jennings, 1973). The factorial approach should be used to determine the amino acids requirements for boilers and layers, and to estimate the requirements of growth or egg production and another body maintenance (Nonis & Gous, 2008; Bonato et al., 2016). The accurate estimation of amino acids is essential if nutritional decisions are to be based on calculations. The calculations in simulation model can be used to predict average food intake per chicken and expected performance (Nonis & Gous, 2008; Bonato et al., 2011). The least square of means value, of 4.80 g lysine/kg diet, determined the slope of the line below the estimated lysine requirement for broiler breeders. The mean requirement of 4.88 ± 0.96 g lysine/ kg diet or 365.6 ± 62.6 mg lysine per broiler breeder hen day was obtained (Coleman et al., 2003).
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2.6 PERFORMANCE OF INDIGENOUS, EXOTIC AND COMMERCIAL