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
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
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
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
||Feed specifications for as-hatched Ross 308 broilers
||Chemical analysis of feed ingredients (As fed basis)
||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
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,
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
|| 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
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
||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.