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Research Article

Comparative Amino Acid Ileal Digestibility of Feed Ingredients Measured with Indigenous and Commercial Strains of Chickens

W. Al-Marzooqi
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Background and Objective: The determination of ileal digestibility has become the preferred method for estimating amino acid availability. This study was conducted to determine the apparent ileal digestibility of amino acids in 3 feed ingredients using commercial and indigenous strains of chickens. Materials and Methods: Three experimental diets, representing three feed ingredients wheat, barley and sorghum were formulated and evaluated using six replicates of five birds per cage at 19 days of age. On day 23, after adaptation to the experimental diets, feed troughs were removed from every cage for 1 h and then reintroduced for 2 h. Then, the birds were killed to sample the ileal digesta from Meckel’s diverticulum to the ileal-cecal-colonic injunction. Results: Broiler birds showed significantly (p<0.001) higher digestibility coefficients and digestible amino acid contents for all the cereal grains than local birds. Of the three cereal grains evaluated in this study, sorghum had the lowest amino acid digestibility coefficient and digestible content for the two bird breeds (p<0.001). The digestibility coefficient and digestible amino acid content estimates for wheat were the highest for both breeds (p<0.001). Conclusion: These data suggest that the classes of chickens significantly influenced the apparent ileal digestibility and digestible amino acid content in the feed ingredients assessed in this study.

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W. Al-Marzooqi , 2020. Comparative Amino Acid Ileal Digestibility of Feed Ingredients Measured with Indigenous and Commercial Strains of Chickens. International Journal of Poultry Science, 19: 396-402.

DOI: 10.3923/ijps.2020.396.402

Copyright: © 2020. This is an open access article distributed under the terms of the creative commons attribution License, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited.


Dietary protein comprises a major element of the cost of poultry feed. In poultry production, it is essential to formulate diets that meet the nutrient requirements of different classes of poultry while minimizing the excretion of excess nutrients into the environment. It is well documented that the contribution of dietary protein to an animal depends not only on its amino acid composition but also on how effectively the amino acids are utilized1. Therefore, describing the proteins in dietary ingredients in terms of the digestible amino acid content rather than the total amino acid content better reflects the amino acid amount actually available for maintenance and production purposes2. It is well recognized that amino acid digestibility is a sensitive indicator of amino acid availability in dietary ingredients for poultry3.

To date, there is a large body of published work on amino acid digestibility coefficients of different feed ingredients4. However, the data are variable due to differences in the methodology used, including the site of measurement5,6.

The use of digestibility values generated from adult rooster assays of dietary formulations for different genetic strains of chickens, especially those with various growth rates, such as local native chickens, may not be an appropriate practice, as the class of bird can influence the digestibility of amino acids in different feed ingredients7. There is a general lack of information on the digestible nutrient contents of local varieties of common cereal grains grown in Oman. Published data on the ileal digestibility of amino acids for these grains are scant. The digestible nutrient contents of these varieties are critical for selection.

All dietary components are important in the formulation of poultry diets but significant attention should be paid to dietary amino acids because controlling the protein status and digestible amino acids has been shown to increase weight gain and feed intake and improve the body composition in broilers8,9.

With the expansion of livestock husbandry practices in Oman, local “indigenous” chicken production is becoming widespread. The economic and social value of local chickens in developing countries of the Middle East, such as Oman especially those in rural areas is well recognized; therefore, it is essential to explore opportunities to improve the production of local chickens10.

The objective of the current study was to assess the digestibility coefficients of amino acids in feed ingredients using commercial and indigenous strains of chickens.


Ethical approval: All experimental work was conducted at the Poultry Research Unit at the Agricultural Experiment Station in accordance with the experimental unit policy on animal welfare and the requirements of the procedures involving animals/birds and their care. The study was approved by the Animal Research Ethics Board at Sultan Qaboos University (IG/AGR/ANVS/05/03).

Ingredients: The local wheat, barley and sorghum grains used in the current study were developed at the Jimah and Wadi Quriyat research stations in Oman. Various developments have been previously described by Al-Bakri et al.11.

Birds and housing: Ninety newly hatched chicks of Cobb 500-type broiler chickens and local Omani chickens were obtained from reputable commercial hatcheries at Barka in Muscat. The birds were housed in suspended grower cages. The cages were located in an environmentally controlled metabolic room maintained at 35°C on day 1, with the temperature reduced by 1°C per day to 22°C. The birds had free access to water and feed and lighting was maintained at a photoperiod of 23 h every 24 h. The birds were initially allocated to replicate cages beginning on day 13, with the live weights of birds in replicates differing by less than 10 g. The birds were fed a crumble commercial broiler diet from day one to day 18. The birds were 19 days old at the commencement of the ileal digestibility assay.

Experimental diets and procedures: Three test ingredients representing three cereal grains wheat, barley and sorghum were ground using a laboratory hammer mill fitted with a 3 mm screen and then incorporated into semisynthetic diets at one rate of inclusion (500 g kg1, Table 1) as the only component containing protein/amino acids (Table 1). Other raw materials were added sequentially with mixing at slow speed (to ensure the effective homogenization of all ingredients).

These diets included the indigestible marker titanium dioxide, a vitamin/mineral premix, vegetable oil and a 50:50 mixture of purified maize starch and glucose (in amounts to make the diets 1000 g kg1). Each of the three experimental diets was evaluated in six replicates, with each cage containing 5 birds. Experimental diets were fed ad libitum for four days from 19-23 days of age.

On day 23, the birds were starved for one hour and then fed for 2 h to ensure sufficient gut fill for digesta sample collection. The birds were then killed by an intracardial injection of sodium pentobarbitone. Following dissection of the lower small intestine, the digesta sample was gently flushed with distilled water and collected into a collection vessel. Samples from birds of the same a cage were pooled to provide a large enough sample for chemical analysis following the procedure described by Al-Marzooqi and Wiseman12.

Calculations: The titanium and amino acid data were used to calculate the coefficient of apparent amino acid digestibility using the following equation, as described by Al-Marzooqi and Wiseman12:


aadig : Amino acid concentration in the digesta

markerdiet : Titanium concentration in the diet

aadiet : Amino acid concentration in the diet

markerdig : Titanium concentration in the digesta

From the coefficients and the amino acid contents of the diet, the concentration of ileal apparently digestible amino acids kg1 was calculated.

Chemical analyses: Samples of test ingredients and ileal digesta samples used for laboratory analysis were ground to pass through a 1 mm mesh in a micro-Wiley mill. Samples of ileal contents were freeze dried prior to grinding. Duplicate determinations of the dry matter, crude protein, ether extract, crude fiber and gross energy content were conducted for the test ingredients according to the AOAC13. The amino acid contents of duplicate test ingredients and ileal digesta samples were determined at Massey University Analytical Laboratory in New Zealand. The amino acid contents were determined by using a Waters ion-exchange HPLC system, utilizing postcolumn ninhydrin derivatization and fluorescence detection, following hydrolysis in 6 M glass-distilled hydrochloric acid containing 0.1% phenol for 24 h at 110+2°C in evacuated sealed tubes. Lysozyme was used as an external standard for the amino acid analysis. Titanium (the inert internal marker) was analyzed following the procedure described by Short et al.14. Chemical analyses were performed in duplicate and repeated if individual data differed by <5%.

Statistical analysis: Data were analyzed by analysis of variance using the general linear model procedure of the Statistical Analysis System (SAS)15 (SAS Institute Inc., versions 2 and 6, 2001). The experimental design was a 2×3 factorial with 2 breeds (Cobb 500 and local Omani chicken) and 3 test ingredients (wheat, barley and sorghum). The main parameters tested in the analysis of variance were digestibility coefficients and digestible amino acid contents. Significant differences between treatment means were assessed using the least-significant-difference procedure. Interactions between the treatments were tested using Tukey's multiple comparisons test when significant and excluded from the model when not significant (p>0.05).


The chemical compositions of wheat, barley and sorghum are summarized in Table 2. The crude protein was higher in wheat than those of barley and sorghum by 6.2 and 21.9%, respectively.

The fiber contents of barley, wheat and sorghum were 68.2, 29.3 and 49.1 g kg1, respectively, which indicates that barley had more fiber than wheat and sorghum by 57 and 28%, respectively. The gross energy content was 4.3% higher in wheat than in the other grains. Sorghum had a higher fat content, as determined by the ether extract, than those of wheat and barley by 40.2 and 29.5%, respectively. The gross energy contents of the three grains were similar.

The amino acid contents of wheat, barley and sorghum are presented in Table 2. Sorghum had lower levels of sulfur-containing amino acids than the other two grains. For the most essential amino acids for poultry performance, wheat and barley contained 26.3 and 22.1% more methionine (1.9 and 1.8 vs. 1.4 g kg1 DM); 19.4 and 21.6% more threonine (3.6 and 3.7 vs. 2.9 g kg1 DM) and 44.7 and 48.8% more lysine (3.8 and 4.1 vs. 2.1 g kg1 DM) than sorghum, respectively. The variations in the amino acid concentrations of the feed ingredients evaluated in this study were largely related to the protein level in the grain. In these grains, the amino acid concentrations generally increased with increasing protein levels. Wheat had higher amino acid concentrations than did barley and sorghum (Table 2).

The mean apparent ileal digestibility coefficients and digestible essential and nonessential amino acid contents determined in the ileum for wheat, barley and sorghum are shown in Table 3 and 4, respectively. For the three feed ingredients evaluated, in comparison to the other two grains, sorghum had the lowest digestibility coefficients and digestible contents (p<0.001) in both breeds of chicken. In general, the class of chickens had a significant effect on the digestibility and digestible amino acid contents (p<0.001). The average digestibility coefficients and the digestible amino acid contents in wheat, barley and sorghum for broilers were higher (p<0.001) than those for local Omani chickens. For broiler birds, the overall mean amino acid digestibility coefficients (and ranges across grains) were 0.84 in wheat (0.71-0.94), 0.72 in barley (0.53-0.92) and 0.67 in sorghum (0.48-0.86), whereas for local birds, the overall amino acid digestibility coefficients (and range across grains) were 0.72 in wheat (0.53-0.89), 0.60 in barley (0.39-0.82) and 0.47 in sorghum (0.21-0.68).

The overall mean amino acid digestible content in g kg1 DM (and range across grains) for broiler birds was 3.23 in wheat (0.82-17.75), 2.41 in barley (0.78-11.50) and 1.92 in sorghum (0.61-7.18), whereas for local birds, the overall mean amino acid digestible content in g kg1 DM (and range across grains) was 2.88 in wheat (0.79-16.78), 2.10 in barley (0.69-10.78) and 1.30 in sorghum (0.30-5.50).