PROJECT RESULTS

Determination of the Digestible Amino Acid Content of Feedstuffs

Applicant: 

Dr. L.D. Campbell
Department of Animal Science
University of Manitoba
Winnipeg, Manitoba  R3T 2N2  Canada

Table of Contents:

• Study 1
• Study 2
• Study 3

ARDI Project:

#00-382

Project Status:

Completed February, 2004

This project is broken down into three separate studies as follows:

• Study 1 - Amino acid composition and true amino acid digestibility values for Western Canadian barley, canola meal and peas.

• Study 2 - Variability in lysine excretion among roosters used in the precision-fed rooster assay for determination of feedstuff amino acid digestibility values.

• Study 3 - Assessment of the effect of heat treatment on amino acid digestibility.

STUDY 1:  Amino acid composition and true amino acid digestibility values for Western Canadian barley, canola meal and peas

Background and Objective:

Protein feedstuffs as a source of amino acids are one of the most costly components of a poultry diet.  Formulation of poultry diets based on digestible amino acid values provides the feed formulator with a cost effective way of meeting the birds’ amino acid requirements and also helps to ensure minimal nitrogen pollution of the environment.

Procedure and Project Activities:

Representative samples of Western Canadian barley, canola meal and peas were obtained and analyzed for constituent amino acids at the University of Manitoba.  Using the precision-fed rooster assay for feedstuff digestibility, assays  researchers Lloyd Campbell and Abolghasem Golian, determined the true amino acid digestibility of the barley, canola meal and pea samples.  In the rooster assay, cecectomized roosters housed in metabolism cages are fed 25-30g of the test sample to determine feedstuff digestibility.  Each sample is diluted based on protein analysis data with non-nitrogen constituents to result in the consumption of 5g protein by each rooster in the assay.  Excreta samples were collected and analyzed to calculate digestibility of individual amino acids.  A correction for endogenous amino acids in the calculation of true amino acid digestibility values is made from an estimate of endogenous amino acid output based on the amino acid excretion of roosters fed a non-nitrogen diet. 

Results and Discussion:

Average values for amino acid content and true amino acid digestibility for the representative Western Canadian feedstuffs are given in Table 1.  Using these values in feed preparation, feed formulators can accurately formulate for digestible amino acids offering them an opportunity to reduce excess crude protein in diets hence reducing the amount of protein waste and decreasing the level of nitrogen release back into the environment by the birds.  Overall both producers and consumers should benefit from the cost effective use of feed ingredients that result in minimal pollution of the environment.

Table 1.  Amino acid composition and true amino acid digestibility (TAAD) of Western Canadian barley, canola meal and peas¹

¹ Values are mean ± standard deviation of fifteen barley, eleven canola meal and ten pea samples.

Acknowledgements:

This research was made possible due to funding from the Governments of Manitoba and Canada through the Canada-Manitoba Agri-Food Research and Development Initiative (ARDI); Maple Leaf Food Inc.; Pioneer Hi-Bred International Inc.; BASF Canada; and the University of Manitoba.

Study 2 - Variability in lysine excretion among roosters used in the precision-fed rooster assay for determination of feedstuff amino acid digestibility values

In the digestibility assay conducted at the University of Manitoba using the precision-fed rooster assay variability in the excretion rate for lysine was noted among roosters.  Variation in lysine excretion rates among birds used in the assay were shown to be 3-4 times higher than that for other amino acids.  The effect was also evident for other basic amino acids (histidine and arginine), as well as for cysteine.  The response appeared to be similar to literature data reports of studies with humans suffering from cystinuria due to a genetic defect for a transporter protein in the kidney responsible for the reabsorption of basic amino acids and cysteine.  Since excreta in birds contains urine as well as feces, the high level of lysine excretion could be associated with an ineffective reabsorption of lysine in the kidney of the birds.

Studies conducted at the University of Manitoba confirmed that the variability noted in the lysine, histidine, arginine and cysteine excretion by roosters was associated with a relatively high content of free amino acids in excreta samples suggesting the kidney reabsorption defect as the cause of the variability in the excretion rate of basic amino acids.  One solution to the problem included the development of methodology for extraction of free amino acids from excreta samples prior to analyses for amino acids of protein origin (i.e. undigested feed protein).  The effectiveness of the methodology for the extraction of free amino acid from excreta samples is shown in Table 2.  A second solution of the problem involved a screening of birds used in the amino acid digestibility assay to determine the extent of variability in lysine excretion.  In this later regard, studies conducted at the University of Manitoba indicated that different group of birds demonstrated different rates of lysine excretion.  Variability within and among groups of birds is demonstrated in the data presented in Table 3.  Consequently it is recommended that laboratories conducting amino acid digestibility assay should determine the extent of variability among birds in lysine extraction rate and use this information to determine if additional methodology should be employed to ensure the precision and accuracy of the assay procedure.

Table 2.  Extraction of free amino acids in excreta from unfed and non-nitrogen diet fed roosters with low (<50mg/48hr) and high (>50mg/48hr) lysine excretion

¹ Data based on the duplicate analyses of 250mg samples of pooled excreta for each group and calculated according to a standard excreta sample (.i.e. normal output over 48hr collection period). Original samples were extracted with 30% ethanol to remove free amino acids.

Table 3.  Amino acid excretion of roosters used in the precision-fed rooster assay showing variation within and among different group of birds

 ¹ Source of birds was from different groups of Single Comb White Leghorn roosters.

Acknowledgements:

This research was made possible due to funding from the Governments of Manitoba and Canada through the Canada-Manitoba Agri-Food Research and Development Initiative (ARDI), Maple Leaf Food Inc, Pioneer Hi-Bred International Inc, and the University of Manitoba.

STUDY 3 - Assessment of the Effect of Heat Treatment on Amino Acid Digestibility

Background and Objective:

Research has shown that vitamin availability following heat treatment using expander technology results in extensive loss of vitamin availability.  The question was posed whether a similar loss of availability of amino acids may occur under similar heat treatment conditions.  A commercial evaluation was conducted to determine whether, under practical conditions using an expander in a pre-pelleting application to control salmonella, there is an effect on amino acid digestibility.

Procedure and Project Activities:

Two feed formulas differing substantially in their ingredient composition were selected.  These formulas were manufactured under normal commercial conditions.  Samples were obtained from both products post-mixing/pre-heat treatment and again as finished product.  Temperatures achieved during expander and pelleting phases were recorded and the expander temperature time was estimated (Table 4).

Table 4.  Expander Retention Time

Feed #1 was a holding diet based upon corn and wheat shorts with no supplemental protein ingredients.  Feed #2 was primarily a corn and wheat based ration with significant addition of protein ingredients (soybean meal, meat meal and canola meal).  It was anticipated that the amino acid digestibility would be greater for Feed #2 than Feed #1.  It was further anticipated that if equipment manufacturers’ claims are to be valid, an improvement in amino acids digestibility might be observed for Feed #1.

The four feed samples were analyzed for both free and total amino acid content.  It was hypothesized that the supplemental amino acids could react during the heat treatment with other ration components.  This would result in the formation of unavailable compounds (ex. Maillard reactions) and there would be a reduction in the free amino acid digestibility as detected by the cecectomized rooster procedure.

Results and Discussion:

In both Feed #1 and Feed #2 no difference in either free supplemental or total amino acids was detected between pre and post heat treatments (Table 5).  Similarly, no notable difference was evident in amino acid digestibility between samples, pre and post heat treatment (Table 6). 

When Feed #1 was compared to Feed #2, it was noted that the digestibility of amino acids was significantly lower in Feed 1.  This stands to reason since Feed #1 contained a high level of wheat shorts that are typically of poorer digestibility.  Feed #2 contained ingredients that are known to be more highly digestible.

Table 5.  Total and Supplemental Amino Acid Content - Pre and Post Heat Treatment

Table 6.  Pre and Post Heat Treatment Percent Amino Acid Digestibilities

Conclusion:

The study indicates that heat treatment through the expander process does not cause a reduction in amino acid digestibility.

Acknowledgements:

This project was made possible due to funding from the Governments of Manitoba and Canada through the Canada-Manitoba Agri-Food Research and Development Initiative (ARDI), Degussa-Huls Corporation and the University of Manitoba. 

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