Ileal Digestible and Metabolizable Energy of Corn, Wheat, and Barley in Growing Japanese Quail

: This study aimed to determine the ileal digestible energy (IDE), apparent metabolizable energy (AME), and nitrogen-corrected AME (AMEn) of three typical cereals for quail chicks with two age periods (day 15–21 and 22–28). The experimental diets comprised a corn–soybean meal reference diet (RD), and three test diets (TD) that were fed to quail chicks in a completely randomized design with ﬁ ve replicates per diet and 15 birds each. The TD comprised corn, wheat, and barley that partly replaced the RD at 300 g/kg (70% reference diet + 30% test ingredient). Age did not in ﬂ uence the IDE, AME, and AMEn values, while the e ﬀ ect of ingredient type was highly signi ﬁ cant on the energy estimates ( p < 0.001). The IDE values of corn, wheat, and barley were estimated as 2924, 3440, and 3184 kcal/kg, respectively. The AME values of corn, wheat, and barley were 3519, 2979, and 2710 kcal/kg, respectively. The estimated AMEn values of corn, wheat, and barley were 3255, 2676, and 2281 kcal/kg, respectively. These ﬁ ndings are crucial for optimizing diet formulations to support quail growth and performance e ﬀ ectively, as they provide valuable insights into the energy content of di ﬀ erent cereals for quail production. Notably, the high IDE and AME values of wheat suggest its potential as a valuable energy source for quail diets. Understanding these values can aid in formulating diets that meet the energy requirements of quail chicks, leading to improved growth rates, feed e ﬃ ciency, and overall productivity in quail production systems.


Introduction
Commonly used in the poultry industry, the metabolizable energy (ME) system is employed to define poultry energy needs, incorporating apparent metabolizable energy (AME) and nitrogen-corrected AME (AMEn) [1].The AME and AMEn values of poultry feed ingredients can be influenced by factors such as age, breed, and diet composition.
Studies have shown that the age of the chicken can impact the AME and AMEn of feed ingredients like soybean meal and canola meal [1,2].Poultry breeds impact the AME and AMEn as well.Many published papers have evaluated numerous grains, like corn and wheat, and have evaluated using cockerel or broilers.However, Japanese quails possess a distinctive digestive physiology with a shorter digestive tract and higher gut pH compared to other poultry species, which makes a difference in AME values for starch in quails compared with broilers.
Japanese quails have unique nutritional requirements compared to other poultry species.They require higher protein levels, particularly during the early growth stages, to support their rapid growth and development [1].The specific energy requirements of quail chicks can vary depending on factors such as age, sex, and production stage [2,3].
Poultry 2024, 3 191 Determining AME values for Japanese quails is crucial due to their unique nutritional needs and digestive physiology.The current study aimed to determine the IDE, AME, and AMEn of corn, wheat, and barley for Japanese quail at two different age periods.

Materials and Methods
This study's experimental protocols were approved by the Research Animal Ethic Committee of the University of Zabol, in line with the "Animal Research: Reporting of In Vivo Experiments" (ARRIVE) guidelines [1].

Bird Management and Experimental Diets
The digestibility, metabolizability, and nitrogen retention of corn, wheat, and barley were studied in a feeding trial with growing Japanese quail at two age periods: 15-21 days and 22-28 days.The proximate and nutrient composition of the tested feed ingredients is shown in Table 1.Two groups of Japanese quail chicks, only one day old, were provided from the experimental farm of the University of Zabol.Afterward, they were placed in floor pens in controlled environments until they were assigned to the experimental groups.The experimental diets comprised a corn-soybean meal reference diet (RD), and three test diets (TDs) that were fed to quail chicks in a completely randomized design, resulting in statistical evaluation with a factorial arrangement of 3 × 2 with five replicates per treatment and 15 birds each.The reference diet was used only as part of the methodology.The temperature was kept at 35 • C on day 1 and then slowly decreased to 29, 26, and 23 • C by the end of weeks 2, 3, and 4. A lighting schedule of 18 h of light and 6 h of darkness was used during the trial.Central ceiling extraction fans and wall inlet ducts controlled ventilation.Birds were given a standard diet from day 0 to day 14 after hatching before being assigned to the experimental diets.A total of 300 quail chicks with a similar body weight (42.6 ± 4.62 g for 15 to 21 days) were present in each age period.The substitution method was used to estimate the IDE, AME, and AMEn of feed ingredients.In this method, a reference diet was formulated to meet or exceed the NRC [2] nutrient recommendations for growing Japanese quails (Table 2).Then, the test diets were formulated by replacing (w/w) 300 g/kg of the reference diet with one of the tested feed ingredients.Experimental diets and water were provided ad libitum to the birds.

Ileal Digestibility Measurements
The ileal digestibility of DM and CP was determined using the marker-assisted method, allowing for the estimation of IDE for each test ingredient.In order to serve as an indigestible marker, the experimental diets were supplemented with titanium dioxide (TiO 2 ) at a concentration of 5 g/kg.The birds (n = 15) were euthanized using CO 2 asphyxiation on days 21 and 28, and their ileal digesta was extracted by gently flushing distilled water into a container.The sample was then placed on ice, frozen at −20 • C, freeze-dried, and ground to a particle size of 0.1 mm.

Metabolizability Measurements
The total excreta collection procedure [3] was employed to assess the metabolizability of DM and CP and estimate the NR, AME, and AMEn of test ingredients.Diets were administered for 7 days in each period, with the first 4 days for adaptation and the following 3 days for data collection [4].The excreta collection was performed twice daily.The collected excreta were pooled within a replicate floor pen (any contamination was removed) and then oven-dried at 105 • C for 24 h ground (0.5-mm screen) and stored at −4 • C for further analysis.   250 Ca (g/kg) 3  8.00 P available (g/kg) 3  3.00 Na (g/kg) 3  1.60 Cl (g/kg) 3  2.60 K (g/kg) 3  9.60 DEB (mEq/kg) 5

Chemical Analysis
The analysis of dry matter (DM) for the test ingredients, test diets, digesta, and collected excreta was conducted using standard procedures (method 930.15;AOAC, 2006).The ash content was examined using a standard procedure (method 942.05,AOAC, 2006).The standard procedure was used to determine crude fiber (method 978.10,AOAC, 2006).To determine the crude fat (method 2003.05), the Soxtec extraction procedure was employed.The crude protein (CP) was assessed using a standard method (method 990.03, [5]).Gross energy (GE) was measured using an adiabatic oxygen bomb calorimeter (Parr Instruments, Moline, IL, USA) that was calibrated with benzoic acid.

Calculations
All data were expressed on a DM basis.The substitution method was used to calculate the IDE (the excreta output was replaced with digesta output and GE of digesta), AME, and AMEn of feed ingredients, as described by Wu, et al. [4]: The AME of the tested feed ingredients was then calculated using the following formula: where P bd and P ti represent the proportion of the reference diet and test ingredient in the test diet, respectively.Based on the composition of the reference diet, P bd and P ti were 0.6876 and 0.30, respectively.Nitrogen retention, as a percentage of intake, was determined: The AMEn was then calculated by correction for zero N retention by assuming 8.22 kcal/g N retained in the body, as described by [3].
The coefficient (C) of apparent ileal digestibility or total tract metabolizability of DM and CP in test diets was determined using the following formula [6]: where T d represents the concentration of titanium dioxide in the diet; T o signify the concentration of titanium dioxide in the output (excreta or digesta); E o shows the nutrient concentration in the output (excreta or digesta); and E d denotes the nutrient concentration in the diet.Thereafter, the ileal digestibility or metabolizability of DM and CP in test ingredients was calculated by a difference method, as described for the AME of test ingredients in Equation ( 3).

Statistical Analysis
Data were analyzed using the one-way ANOVA with SAS [7] in a completely randomized design with a factorial arrangement of 3 × 2: where Y ijk represents the observed response variable for the ith level of the ingredient, the jth level of the age, and the kth replicate; µ is the overall mean; τ i is the effect of the ith level of the ingredient; ß j is the effect of the jth level of the age; ε ijk is the random error term.Pen was treated as the experimental unit, and test diets and age were the fixed effects included in the model.Treatment means were calculated using the LSMEANS statement adjusted for Tukey's test to separate the statistical differences among the treatments.Differences were reported as significant at p < 0.05.Before conducting ANOVA, we assessed the normality and homogeneity of variances in the data using Shapiro-Wilk and Levene's tests, respectively.The correlation between the AME:IDE ratio and CP content of the ingredients was assessed by the REG procedure of SAS [7].

Ileal Digestibility and Total Tract Metabolizability
The ileal digestibility of DM (iDM) and CP (iCP) and the metabolizability of DM (mcDM) and CP (mcCP) are shown in Tables 3 and 4, respectively.Feed type significantly affects the ileal digestibility of iDM (p < 0.001), where the highest iDM was attributed to wheat (88.1%), followed by barley (84.6%) and corn (73.6%).The interaction of feed × age affects the ileal digestibility of CP (p = 0.003), where the iCP in corn (56.1 to 74.0%) and barley (69.0 to 84.0%) diets was increased with increasing age.The main effect or interactive effect of feed and age was not significant on the mcDM and mcCP (Table 4); however, the mcCP showed a decreasing trend with advancing age (85.1 to 79.7%; p = 0.098).The interaction of feed × age affects the NR, where the NR was deceased with advancing age in corn (86.2 to 74.7%) while it was increased with increasing age in barley (81.7 to 87.8%).Means in a column not sharing a common letter (a-c) are significantly different (p < 0.05). 1 Each value is the mean of five replicate pens with 15 birds per pen.

The IDE, AME, and AMEn of Feed Ingredients
Although age did not influence the IDE, AME, and AMEn values, the ingredient type was highly significant in the energy estimates (p < 0.001).It should be noted that age showed an increasing trend on AME (p = 0.077), while a decreasing trend on AMEn (p = 0.081).The estimated IDE of corn, wheat, and barley in younger quails (15 to 21 d) were 2954, 3441, and 3194 kcal/kg, respectively, and the corresponding values in older quails (22 to 28 d) were 2894, 3439, and 3173 kcal/kg, respectively (Table 3).According to the estimates (Table 4), the AME values of corn, wheat, and barley in younger quails (from 15 to 21 d) were 3340, 2899, and 2663 kcal/kg, respectively, while in older quails (from 22 to 28 d), the corresponding values were 3698, 3058, and 2757 kcal/kg, respectively.The AMEn values of corn, wheat, and barley in younger quails (from 15 to 21 d) were 3300, 2831, and 2506 kcal/kg, respectively, while in older quails (from 22 to 28 d), the corresponding values were 3210, 2521, and 2056 kcal/kg, respectively.Age significantly affects the ∆AME (AME − AMEn), where it increased from 88.6 to 576 kcal with advancing age (p < 0.001).The AME: IDE ratio (y) negatively correlated with CP (x; %) content of the cereals: y = 15.29 − 5.77x; R² = 0.721.

Discussion
The present study aimed to determine the IDE, AME, and AMEn values of three main cereals (i.e., corn, wheat, and barley), as the principal energy sources for Japanese quails.Unfortunately, no data on the AMEn values of the studied feed ingredients for Japanese quail chicks are available, so a comparison with the AMEn values of the feed ingredients for broiler chickens may be the only reference point available.
The findings of the present study highlight significant variations in AME and AMEn values across different feed ingredients and age groups, underscoring the complexity of nutrient utilization in poultry.For a more thorough understanding of the underlying biological or physiological mechanisms driving these observations, it is crucial to examine the impact of dietary components, such as non-starch polysaccharides (NSPs).Exploring the implications of these findings on practical feeding strategies or feed formulation is warranted.The effects of non-starch polysaccharides (NSPs) on the energy values of corn, wheat, and barley in Japanese quails are complex and influenced by various factors.Corn, wheat, and barley have different NSP contents, which can affect their digestibility and energy values.For example, corn has a lower NSP content compared to wheat and barley, which can make it more digestible [8,9].The digestibility of NSPs in Japanese quails can vary depending on factors such as the type of NSP, the age of the bird, and the enzymes in the diet.It was found that the digestibility of NSPs in Japanese quails was influenced by the type of NSP and enzymes in the diet [10].The age and sex of Japanese quails can also influence the effects of NSPs on energy values.For example, a study by Nóbrega et al. [9] found that the rate of passage in the gastrointestinal tract of Japanese quails was influenced by sex and apparent metabolizable energy (AMEn) content in the diet.
Although the lowest IDE value was observed for corn and the highest IDE was estimated for wheat, among the studied ingredients, the highest AME and AMEn were obtained for corn, which was under the lowest ileal digestibility of DM and CP in corn.One plausible reason may be that a lower ileal digestibility of DM and CP can lead to higher AME and AMEn values for corn by providing more available nutrients in the lower part of the intestine and resulting in higher AME or AMEn values than IDE.Our data showed that there was a negative correlation between the AME:IDE ratio and the CP content of the cereals, and each percent increase in CP resulted in a 5.77 unit decrease in the AME:IDE ratio.The negative correlation between the ratio of AME:IDE and the CP content of ingredients in poultry is related to the energy available for the bird's growth and maintenance.AME is the energy available for the bird's metabolism, while IDE is the energy that is not absorbed and is excreted, and CP is a source of energy but also a source of nitrogen for the bird's growth.When the CP content of ingredients is high, the bird's metabolism is focused on the digestion and utilization of nitrogen, which can reduce the energy available for growth and maintenance.This is because the bird's metabolism requires energy to digest and absorb the nitrogen from the CP, which can reduce the energy available for other metabolic processes.Furthermore, the efficiency of AME for net energy (NE) in broilers is affected by the CP content of the diet.As the CP content decreases, the efficiency of AME for NE increases, which can also contribute to the negative correlation between the AME:IDE and CP content [11].Another study by Wu et al. [12] found that the NE content was positively related to AME and ether extract, but negatively to crude protein.This suggests that, as the CP content of ingredients increases, the energy available for the bird's growth and maintenance decreases.This is supported by several studies, such as the one by Toghyani et al. [13], which found that the AMEn values of expeller-extracted canola meal (ECM) were negatively correlated with its composition and AME content for broiler chickens.The study also found that the IDE value was only 2.2% higher than the AME value, indicating that a significant portion of the energy in the ECM was not available for the bird's metabolism.
Although bird age is a determinant factor affecting the AMEn in growing birds [14], we could not find any significant improvement in the AMEn of the studied feed ingredients.In the study of Khalil et al. [14], the AMEn quadratically changed with the increasing age of broilers, while the behavior of AMEn in most cereals plateaued during the third and fourth week of age, which agreed with our findings.In the current study, the AMEn values of cereal grains did not differ between weeks 3 and 4, which was associated with equal NR in the two age groups, suggesting that the potential of the quail chicks to metabolize energy could not be different between the third and fourth week of age.
It has been shown that the penalty imposed by the N correction to the AME in cereals such as corn, wheat, and barley was 1.02, 2.56, and 6.71%, respectively.This lower AME penalization in cereal grains compared with protein-rich sources is expected, based on their lower protein content and N retention [15].Apart from the higher N retention in younger chicks and less catabolism of the retained protein in the body compared to older birds [16], the protein metabolizability also decreased with advancing age in the present study, which could be justified by significant increases in feed intake in older chicks (Figure 1).Lopez and Leeson [16] showed that feed intake in broilers continues to increase.In contrast, the N retention declines as birds grow over time, and higher feed intake increases the passage rate while decreasing the retention time, leading to lower CP digestibility.However, different ages of poultry may have variable abilities to digest and metabolize feed components [17].Some limiting factors, including the secretion and activities of digestive enzymes and the surface area for absorption in younger chicks, are overcome with advancing age, resulting in better nutrient utilization in older broilers [18,19].However, this may not be valid in our case, possibly due to the close age difference between quail chicks in the present study.
In the current study, the AMEn values of corn in quail chicks were compared with those values determined in broiler chickens by Lopez and Leeson [20].The AMEn of corn for quail chicks in the present study (ranging from 3210 to 3300 kcal/kg) was comparable to those reported for broiler chickens (ranging from 3162 to 3459 kcal/kg; Figure 2).The same was observed for the AMEn of wheat, where the estimated values of AMEn for quail chicks were comparable with those reported for broiler chickens (Figure 2).The reported AMEn of wheat for starting broiler chickens by Del Alamo, et al. [21] ranged from 2876 to 2982 kcal/kg, and Khalil et al. [22] estimated that the AMEn of wheat was 2576, which was close to our estimations.Comparing our estimates of the AMEn of barley also indicated that there was no difference between the AMEn of barley for broiler chickens and growing quail chicks (Figure 2).The AMEn of barley for broiler chickens ranged from 2369 kcal/kg [22] to 2654 kcal/kg [23], 2682 kcal/kg [24], and 2841 kcal/kg [25].The AMEn of the corn, wheat, and barley in quail chicks did not differ from those values in broiler chickens, showing that both growing quail and broiler chickens may equally use these cereal grains for energy extraction.However, some morphological differences, such as the length of the intestine and passage rate, likely affect the energy utilization of various classes of birds.For example, a longer intestine and subsequently slower passage rate in a laying hen intestine may result in higher energy utilization in layers compared to broilers [26].
that there was no difference between the AMEn of barley for broiler chickens and growing quail chicks (Figure 2).The AMEn of barley for broiler chickens ranged from 2369 kcal/kg [22] to 2654 kcal/kg [23], 2682 kcal/kg [24], and 2841 kcal/kg [25].The AMEn of the corn, wheat, and barley in quail chicks did not differ from those values in broiler chickens, showing that both growing quail and broiler chickens may equally use these cereal grains for energy extraction.However, some morphological differences, such as the length of the intestine and passage rate, likely affect the energy utilization of various classes of birds.For example, a longer intestine and subsequently slower passage rate in a laying hen intestine may result in higher energy utilization in layers compared to broilers [26].wheat, and barley in quail chicks did not differ from those values in broiler chickens, showing that both growing quail and broiler chickens may equally use these cereal grains for energy extraction.However, some morphological differences, such as the length of the intestine and passage rate, likely affect the energy utilization of various classes of birds.For example, a longer intestine and subsequently slower passage rate in a laying hen intestine may result in higher energy utilization in layers compared to broilers [26].The present study reflects that the difference between AME and AMEn (∆AME) was higher in older quails than in younger birds.In fact, the difference between AME and AMEn represents the energy that is retained in the body as nitrogen, which is a valuable nutrient for growth and development.The higher ∆AME means a higher penalty imposed on the AME by N correction, which shows that more energy is retained in the body as nitrogen.Khalil et al. [14] found that the AMEn of a corn-soy diet increased numerically by 98 kcal/kg from d 14 to 21, indicating a higher penalty imposed on the AME by N correction in older birds, which agreed with our results.However, Abdollahi et al. [15] stated that the N correction can also penalize the energy value of cereal grains, with the penalty ranging from 1.69% in maize to 2.46% in barley, which was close to our findings in the present study.These studies demonstrate that the ∆AME is an important indicator of the energy retained in the body as nitrogen and that a higher penalty imposed by N correction shows a higher retention of energy as nitrogen.The older birds retain more nitrogen compared to younger birds, which is consistent with the fact that older birds have a higher body weight and muscle mass compared to younger birds [15,16,27].

Conclusions
This study investigated the nutrient utilization of Japanese quail-fed cereal grains.Corn exhibited superior ME values than wheat and barley in growing quail chicks.Agerelated changes were noted, particularly in protein metabolizability, which tended to decrease with advancing age, while nitrogen retention remained consistent across treatments and age groups.The AME values of corn, wheat, and barley were 3519, 2979, and 2710 kcal/kg, respectively.The estimated AMEn values of corn, wheat, and barley were 3255, 2676, and 2281 kcal/kg, respectively.Future research should focus on optimizing feed formulation for quail hicks, exploring alternative energy sources, and considering age-specific nutrient requirements to enhance quail performance and production efficiency.This study contributes valuable insights for the quail industry, guiding future research towards more effective diet strategies for improved profitability.

Figure 1 .Figure 1 .
Figure 1.Comparison of the feed intake in quail chicks in the third (3rd) and fourth (4th) weeks of age.

Figure 1 .
Figure 1.Comparison of the feed intake in quail chicks in the third (3rd) and fourth (4th) weeks of age.

Figure 2 .
Figure 2. One sample t-test of the determined apparent metabolizable energy corrected for zero nitrogen (AMEn) of corn, wheat, and barley in quail chicks with the AMEn values reported in broiler chickens.

Table 1 .
Nutrient content of feed ingredients (g/kg; as received basis).

Table 2 .
Composition of the reference diet.
Means in a column not sharing a common letter (a-c) are significantly different (p < 0.05).1Eachvalue is the mean of five replicate pens with 15 birds per pen.