Abstract: In order to evaluate the effects of different levels of energy and methods of formulation of Amino Acid (AA) requirements of diets, this experiment was conducted using 392 broiler chicks. The experiment was carried out using a complete randomize block design with 7 levels of energy 3175, 3075, 2975, 2875, 2775, 2675 and 2575 kcal kg-1 for grower diet and 3225, 3125, 3025, 2925, 2825, 2725 and 2625 kcal kg-1 for finisher diet and two methods of formulation of diets AA requirements (total and digestible) as a factorial arrangement. Results showed that by increasing level of energy feed intake, body weight and FCR were promoted in grower diet (p<0.05). Effect of decreasing level of energy up to 2725 and 2825 kcal kg-1 was not significant on body weight and FCR in finisher diet, respectively. Formulating of diet based on total or digestible AA affected feed intake and FCR in finisher diet (p<0.05). Interaction effect of independent factors affected on body weight in grower diet (p<0.05). Decreasing level of energy increased gastrointestinal tract percentage weight (p<0.05). Formulation of diet based on digestible AA decreased gastrointestinal tract percentage weight (p<0.05). Abdominal fat decreased significantly as ME content of diets decreased. Results showed that it`s possible to reduce the level of energy up to 3175 kcal kg-1 in grower and 2725 kcal kg-1 in finisher diet for giving the best and economical performance response. Formulation of diet based on digestible AA in finisher diet resulted in promotion of performance.
INTRODUCTION
Energy is not a nutritive substance, rather is a quality or property which exists in nutritive food and is released by oxidation. The first step in diet formulation for chicks is selecting diet energy level which is often considered as the basis for selecting the thickness of the nutritive feed (National Research Council, 1994).
Animals, e.g., birds, consume food to fulfill the internal requirement to energy. Food intake is then terminated when this internal requirement is satisfied.
Therefore, the appropriate proportion between energy requirement level and the nutritive substances of the diet (which is a theory) has a logical explanation and is necessary for attaining the best performance in birds feeding (Leeson and Summers, 2001).
In addition to maintaining the appropriate energy level for attaining the best outcome, there must be an appropriate balance between energy and protein. Proteins are composed of various amino acids. In order to supply amino acids requirements for chicks to reach at maximum grower, formulating diets using various crude proteins is a must. Today, the challenge of using multiple proteins is resolved by formulating diets based on amino acids and then adding synthetic amino acids to the diet (Maiorka et al., 2004). On the other hand, amino acids existing in foods are not fully digestible by chicks and the capability of different foods in digesting amino acids varies. Therefore, it is obvious that comparing foods based on digestible amino acids provides a more accurate measure for their relative nutritive value in total required amino acids (Farrell et al., 1999; Parsons, 1991).
In many developing countries, formulating diets using foods having high capability of digesting amino acids (corn and soybean meal) and high energy levels results in cost price increaser.
We therefore face this question: By formulating diets based on digestible amino acids, is it possible to employ diluted diets of foods like wheat, barley and bran wheat, while observing no significant effect on broilers performance?
For answering this question, also attention to energy importance and connection of energy with amino acid in diet, this study was conducted to evaluate appropriateness of formulation of corn soybean meal based diet on the basis of total and digestible AA requirement when diets had varying levels of metabolic energy.
MATERIALS AND METHODS
All of the experimental procedures were conducted in the Poultry Lab and Nutrition Lab of the Tehran University between 2006 and 2007. A total of 392 as hatched Ross 308 broiler chicks were used in this study. Chicks were reared on floor pens from day old to 10 days of age and received a standard starter diet (3010 kcal kg-1 ME and 23% CP), Then after being subjected to an overnight period of feed withdrawal, chicks were weighted individually and transferred to battery cages (40x78x90 cm) and allocated to dietary treatments so that pens had equal initial weight and weight distribution. Four replicate groups of 7 chicks were fed each of dietary treatments. Experimental period began at 10 days of age and lasted in 49 days of age. The experiment was carried out using a complete randomize block design with a 7x2 factorial arrangement. Factors were included different levels of energy (7 energy levels) and methods of formulation of diets AA requirements (total and digestible). Chicks received a grower diet from 10-28 days of age and a finisher diet from 28-49 days of age. Seven levels of ME used for formulation of diets in grower period were 3175, 3075, 2975, 2875, 2675 and 2575 kcal ME per kg of diet. Energy level in finisher period began with 2625 and increased by 100 kcal to achieve 3225 kcal. As diets were diluted, the ratio between ME and other nutrients were kept fix. For each ME level, two method of formulation of AA requirements of diets (total and digestible AA requirement) were employed. All the diets met or exceeded nutrients recommended by Ross management manual (Table 1). Before formulation of diets, feed ingredients were analyzed for CP, total P, Ca and ether extract according to the AOAC procedures (1995), data showed in Table 2. Diets used in this study in finisher period are presented in Table 3. The same ingredients were used for formulation of diets in finisher period.
Body weight and feed consumption were measured at 28 and 49 days of age and then weight gain and feed conversion ratios were calculated. At the termination of experiment, 2 birds from each replicate were selected randomly and were slaughtered and their empty carcass weight in relation to body weight (%), gastrointestinal tract, abdominal fat, liver and heart were expressed as percentage of the carcass weight.
Data were statistically evaluated by the analysis of variance procedure of SAS software (1998), involving a factorial arrangement of main factor (energy level and method of formulation of AA requirements) in a complete randomize block design. Significant differences between
| Table 1: | Feed specifications for as-hatched Ross 308 broilers |
| Table 2: | Chemical analysis of feed ingredients (As fed basis) |
| Table 3: | Composition and nutrient content (g kg-1) of experimental diets in finisher (28-49 days) period |
| D: Diet formulation based on digestible amino acid, T: Diet formulation based on total amino acid, D (AA): Digestible amino acid | |
means were separated by the GLM procedure of SAS software (1998). Means were compared using Duncan`s multiple-range test and significance was determined at p≤0.05 (Duncan, 1955).
RESULTS AND DISCUSSION
Feed intake was not significantly influenced by the way amino acid requirements were expressed in grower period (11-28 days) (Table 4), which is consistent with previously published results from experiments comparing diets based on alternative ingredients with low amino acid digestibility to diets based on ingredients with high amino acid digestibility (corn and soybean meal) and to diets with low digestibility ingredients supplemented with synthetic amino acids (Rostagno et al., 1995; Dari and Penz, 1996).
Formulation of finisher diet based on total or digestible AA had significant effect on feed intake (p<0.05). Diet formulation based on digestible AA resulted on decreasing feed intake in finisher period (Table 4). It seems that, reduced food intake observed in formulated rations based on digestible AA, is due to ability of this formulation method to balance rations close to broilers requirements, because amino acids existing in foods are not fully digestible by chicks and the capability of different foods in digesting amino acids varies. As reported by other researches Parsons (1991) and Fernandez et al. (1995), by increasing the amount of food intake in the finisher period, the superiority of diets formulated based on digestible amino acids in formulating more balanced diets was observed. The diet energy level had significant effect on the amount of food intake in grower period (p<0.05). By decreasing the diet energy
| Table 4: | Performance of broiler fed diets formulated based on total and digestible amino acid |
| abc: Means in the same column with a different superscript are significantly different (p<0.05) | |
level, the amount of food intake decreased also (Table 4). This decrease was due to the required increment in the amount of food intake which encountered the barrier of low capacity of chicks GIT, while the latter was the consequence of insufficient grower of chicks in the ages of 11 to 28 days, which is in accordance with results obtained by National Research Council (1994).
The amount of food intake in the finisher period was not influenced by the diet energy level (Table 4). Sunder et al. (1988) proved that there is a reverse relationship between capacity of GI tract and diet energy level. Therefore, consuming dilute energy in the starter period allowed chicks to meet their total energy requirements by having more food intake in the finisher period and showed that, by taking low-calorie diets, chicks consume energy more efficiently. Thus an increase of 100 kcal kg-1 of energy in the finisher period diets along with more efficient energy consumption resulted in no significant influence on the amount of food intake in the finisher period.
Diet formulation based on amino acids had no significant effect on the weight gain of chicks in the grower and the finisher periods (Table 4). This is in accordance with results obtained by other researchers (Maiorka et al., 2004; Farrell et al., 1999; Dari and Penz, 1996).
The diets energy level had significant effect on chicks weight gain in the grower period (p<0.05). By decreasing the diet energy level, the rate of weight gain of chicks was reduced (Table 4). The results showed that the best energy level in the grower period is 3175 kcal kg-1. Researchers have reported that, especially in grower period, broilers weight gain is influenced by diet energy level and therefore, high energy-level diets in comparison with low energy-level ones result in significant increment in the rate of grower (Donaldson, 1985; Hussein et al., 1996; Leeson et al., 1996).
By increasing the diet energy level in the finisher period, weight gain was improved but this was not statistically significant (Table 4). Hence, the diet can be diluted up to 2725 kcal kg-1 in the finisher period.
Increment food intake in finisher period (28-49 days) along with more efficient energy consumption resulted to same weight gain in all levels of energy diet (Olumu and Offiong, 1980). Method of diet formulation based on AA had no significant effect on feed conversion ratios in grower and finisher periods (Table 4). These results obtained in previous researches (Farrell et al., 1999; Fernandez et al., 1995; Maiorka et al., 2004).
Feed conversion ratios had better with diet formulation based on digestible AA in finisher period (p<0.05) (Table 4). These result showed when diet formulation based on digestible AA was balanced, provided chicken requirements and reduced food in take. Results showed that by increasing levels of energy in diet feed conversion ratios was decreased in grower period (p<0.05). Because decreasing level of energy diet had significant effected on broiler efficiency on grower period (Sizemore and Siegel, 1993; Pirgozlieve and Rose, 1999). Feed conversion ratios had no influence significant decreasing level of ME diet until 2725 kcal kg-1 in finisher period (Table 4). These result was agreement whit those obtained by Leeson et al. (1996).
Interaction effect of independent factors affected just on weight gain in grower period (p<0.05). The evaluation of the contrasts showed that the formulation of diet based on digestible AA was best when diets contained the low energy level. For rations with low energy level, we usually
| Table 5: | Carcass yields of broiler fed diets formulated based on total and digestible AA with different levels of ME |
| abc: Means in the same column with a different superscript are significantly different (p<0.05) | |
use low digestible food stuff. So, formulation according to digestible AA is close to chickens requirements and chickens that feed with these rations (low energy levels), have suitable performance.
Carcass yield of broiler received dietary treatment are shown in Table 5. Results showed that formulation based on AA did not influence carcass yield, independent of the dietary energy level (Table 5). Also interaction effect of energy and method of diet formulation had no significant on carcass yield (Maiorka et al., 2004, 2005). Level of ME diet had significant effect on GIT (p<0.05), diet contained low energy levels eventuate increasing GIT weight (Table 5). Results Diet formulation method (digestible or total amino acids based) had significant effect on the weight share of digestive system from total body mass (p<0.05) and this ratio was lower in chicks fed by the diet formulated based on digestible amino acids. This is in accordance with the results of previous studies (Sunder et al., 1988; Waldroup et al., 1990). As diets energy level increased, abdominal fat pad increased significantly (p<0.05). Diet formulation based on amino acids had no significant effect on abdominal fat pad (Table 5). As many previous experiments have reported, abdominal fat pad increases as diet energy level goes up (Maiorka et al., 2004; Farrell et al., 1999; Rostagno et al., 1995).
Liver weight share from total body mass was not affected by formulation method or diet energy level (Table 5). In high energy-level diets, formulation based on amino acids had no negative effect on liver, which is in accordance with Mairoka et al. (2004) findings. Heart weight share from total body mass was affected by diet energy level (p<0.05).These result may be related to higher metabolism in chicks fed high density diets (Table 5). The results of this study demonstrate that employing thick diets in grower period (ages of 11 to 28 days) and using diets diluted up to 2725 kcal kg-1 and formulated based on digestible amino acids in finisher period results in performance improvement and by reducing cost price leads to significant economical benefits.