Prediction of the apparent ileal digestible amino acid contents of canola meal for broilers from crude protein content

X. Li; Y. M. Sun; D. Zhang; K. H. Huang; V. Ravindran; W. L. Bryden

doi:10.1071/AN24138

RESEARCH ARTICLE (Open Access)

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Prediction of the apparent ileal digestible amino acid contents of canola meal for broilers from crude protein content

X. Li

^A ^* , Y. M. Sun

^A , D. Zhang ^A , K. H. Huang ^B , V. Ravindran ^C and W. L. Bryden

^A ^D

+ Author Affiliations

- Author Affiliations

^A School of Agriculture and Food Sustainability, University of Queensland, Gatton, Qld 4343, Australia.

^B Ridley Agriproducts Ltd Pty., 565 Bourke Street, Melbourne, Vic, Australia.

^C Monogastric Research Centre, School of Agriculture and Environment, Massey University, Palmerston North 4442, New Zealand.

^D Queensland Alliance for Agriculture and Food Innovation, University of Queensland, St Lucia, Qld 4072, Australia.

^* Correspondence to: x.li1@uq.edu.au

Handling Editor: Kapil Chousalkar

Animal Production Science 64, AN24138 https://doi.org/10.1071/AN24138

Submitted: 26 April 2024 Accepted: 15 August 2024 Published: 9 September 2024

© 2024 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

Context

Canola meal is a protein-rich feedstuff with an amino acid profile that is reasonably well balanced and has the potential to replace soybean meal in poultry diets.

Aim

The objective of the present study was to investigate the relationship between the crude protein content and apparent ileal digestible amino acid contents of Australian canola meals.

Methods

Thirteen canola meal samples, processed by expeller or solvent extractions, were collected. The digestibility assay diets were based on dextrose and contained canola meal as the sole source of protein. The proportions of dextrose and canola meal were varied in each diet to obtain ~200 g/kg crude protein. Each diet was fed to three cages of six 35-day-old broilers for 7 days. At the end of the assay, digesta from the terminal ileum was collected for digestibility determination.

Key results

Crude protein contents were positively correlated with amino acid contents (P < 0.05 to 0.001), except that of serine (r = 0.43; P = 0.11). Significant correlations between the crude protein content and ileal digestible contents were observed for most of amino acids, with coefficients of >0.80 (P < 0.05 to 0.001). Low correlation coefficients were observed for lysine (r = 0.48; P = 0.11) and serine (r = 0.55; P = 0.06). The poor correlation for lysine may be reflective of reduced lysine availability during processing.

Conclusions

The results showed that the crude protein content of canola meal could serve as a predictor of apparent ileal digestible content of most amino acids for broiler chickens.

Implications

Regression equations developed in the present study could be used to predict the content of ileal digestible amino acids in canola meal by using analysed crude protein contents.

Keywords: broilers, canola meal, correlation, crude protein, digestible amino acids, prediction.

Introduction

Provision of adequate digestible amino acids is critical in diet formulations for poultry. The steady expansion of global poultry production increases the demand for a diverse range of ingredients to supply the protein in poultry diets. In Australia, canola (Brassica napus) has emerged as an important crop for both the human-food and animal-feed sectors (Spragg 2018). Canola has received much attention during recent decades, especially through breeding programs to improve the yield, oil stability, climate resilience, disease resistance and, to reduce erucic acid in the oil and glucosinolates in the meal (Potter et al. 2016; Salisbury et al. 2016). The plant toxins in rapeseed, the progenitor of modern canola varieties, were major deterrents to the use of rapeseed meal in poultry diets (Bell 1984). However, canola seeds are mainly used as a source of high-quality oil for human consumption, whereas the meal accounting for 60% of the whole canola seed is used as a protein source for livestock and poultry (Bell 1993; Khajali and Slominski 2012).

The amino acid profile of canola meal is reasonably well balanced (Spragg and Mailer 2007; Khattab and Arntfield 2009; Khajali and Slominski 2012), but digestibility of amino acids is key to the value of canola meal as a protein source for poultry. The importance of considering the availability of amino acids in commercial feed formulations has become accepted practice as diets formulated on digestible amino acid values are superior to those based on total amino acids (Ravindran and Bryden 1999; Lemme et al. 2004; Bryden and Li 2010). Amino acid analysis and in vivo digestibility assays are costly and time consuming for routine feedstuff evaluation. It would be of great benefit to the poultry industry if the digestible amino acid content of canola meals could be deduced from its crude protein content, which is routinely determined. The primary objective of the present study was, therefore, to investigate the relationship between crude protein content and ileal digestible amino acid content of Australian canola meals.

Materials and methods

The experimental procedures were approved by the Animal Care and Ethics Committee of the University of Queensland and complied with the Australia Code of Practice for the Care and Use of Animals for Scientific Purposes (NHMRC 2013).

Amino acid digestibility assay

Experimental diets

The experimental diets were formulated as outlined by Ravindran et al. (2005). Thirteen canola meal samples were collected from commercial sources in Victoria and New South Wales. The samples included four expeller-extracted meals and nine solvent-extracted meals (Table 1). Canola meals were incorporated as the sole source of dietary protein in experimental diets and the dextrose proportion varied in experimental diets so that each diet contained ~200 g/kg of crude protein (Table 1). All diets contained, per kilogram, 19 g dicalcium phosphate and 10 g limestone. No attempt was made to balance the dietary contents of calcium and phosphorus. Celite (Celite Corporation, Lompoc, CA, USA), a source of acid-insoluble ash (AIA), was added (20 g/kg) to all diets as an indigestible marker (Table 1).

Table 1.Crude protein content of canola meal and the composition of amino acid digestibility assay diets (g/kg air dry basis).

Ingredient	1	2	3	4	5	6	7	8	9	10	11	12	13
Canola meal
Crude protein (nitrogen × 6.25)	277	291	297	312	340	350	351	355	365	370	379	388	394
Composition of assay diets
Canola meal^A	723	687	673	641	589	571	570	563	548	540	528	516	508
Dextrose^A	156	192	206	238	290	308	309	316	331	339	351	364	371
Vegetable oil	60	60	60	60	60	60	60	60	60	60	60	60	60
Celite^B	20	20	20	20	20	20	20	20	20	20	20	20	20
Dicalcium phosphate	19	19	19	19	19	19	19	19	19	19	19	19	19
Limestone	10	10	10	10	10	10	10	10	10	10	10	10	10
Choline chloride	3	3	3	3	3	3	3	3	3	3	3	3	3
Salt	2	2	2	2	2	2	2	2	2	2	2	2	2
Vitamin–trace mineral premix^C	7	7	7	7	7	7	7	7	7	7	7	7	7
Total	1000	1000	1000	1000	1000	1000	1000	1000	1000	1000	1000	1000	1000

Samples 1–4 were expeller-extracted and Samples 5–13 were solvent-extracted.

^A Proportions of canola meal and dextrose were varied to supply 200 g of crude protein per kilogram of diet.

^B Source of acid-insoluble ash.

^C Each kilogram of premix contained: vitamin A, 4.8 mIU; vitamin D₃, 0.96 mIU; vitamin E, 10 g; vitamin K₃; 0.8 g; riboflavin, 5 g; pyridoxine, 2.4 g; cyanocobalamin, 6 mg; biotin, 0.06 g; niacin, 24 g; thiamine; 0.8 g; pantothenic acid, 6 g; folic acid, 0.6 g; magnesium, 40 g; manganese, 40 g; zinc, 32 g; iron, 32 g; copper, 4 g; iodine, 0.2 g; cobalt, 0.04 g; selenium, 0.04 g; molybdenum, 0.04 g; antioxidant, 50 g; liquid Paraffin white, 10 g.

Birds

Day-old, male, broiler (Cobb) chicks were obtained from a local hatchery and housed in a brooder in an environmentally controlled room. Room temperature was maintained at 32°C during Week 1 and gradually decreased to ~23°C by the end of Week 3. A temperature of about 21°C was maintained to the end of the experimental period. The birds received a commercial broiler starter diet (230 g crude protein/kg) from Day 1 to Day 21. On Day 22, birds were transferred to cages housed in thermostatically controlled rooms (23°C) and fed a commercial broiler finisher diet (180 g crude protein/kg) from Day 22 to Day 35 post-hatch. Feed and water were offered ad libitum. On Day 35, the birds were weighed and the birds with bodyweights close to the mean were selected, and each test diet was randomly allocated to three cages of six birds each. The diets were offered ad libitum from Day 35 to Day 42 post-hatch.

Digesta sampling

On Day 42, all birds were euthanised by an intracardial injection of diluted sodium pentobarbitone solution, and the contents of the lower half of the ileum were collected by gently flushing with distilled water into plastic containers. The ileum is defined as the portion of the small intestine extending from vitelline diverticulum to a point 40 mm proximal to the ileo–caecal junction. The ileum was further divided into upper and lower portions of equal length. Samples from all birds within a cage were pooled, frozen immediately after collection and subsequently freeze-dried. Diet and dried ileal digesta samples were ground to pass through a 0.5-mm sieve and stored in airtight containers at −20°C before chemical analyses.

Chemical analysis

The nitrogen (N) content of canola meals and, the diet and ileal digesta samples was determined using a FP-428 nitrogen determinator (LECO® Corporation, St Joseph, MI, USA), according to the procedures of Sweeney (1989). The N content was multiplied by 6.25 to obtain the crude protein (CP) content. AIA content of the diet and ileal digesta samples was determined using the method of Mollah et al (1983).

Amino acid content of diet and ileal digesta samples were determined by high-performance liquid chromatography as described by Li et al (2006). Briefly, samples containing 80 mg CP were hydrolysed under N with 8 N hydrochloric acid containing phenol (3 g/L) at 120°C under a pressure of 15 psi at 121°C for 16 h. DL-norleucine was added to the hydrolysate as an internal standard. Each hydrolysate was then diluted and adjusted to pH 2.2–2.3, the same as the amino acid standard (Standard H, Pierce Chemicals Co., Rockford, IL, USA). The hydrolysates were passed through a 0.22-μm nylon 66 membrane filter (Alltech, Baulkham Hills, New South Wales, Australia). Aliquots of the hydrolysates were then subjected to ion-exchange column chromatography, using a Shimadzu amino acid analysis system (Shimadzu Corporation, Kyoto, Japan). Amino acids were eluted by a gradient of pH 3.20 sodium citrate eluent to pH 10.0 sodium citrate eluent at a flow rate of 0.3 mL/min and a column temperature of 60°C. Chicken egg-white lysozyme (Seikagaku Co., Chuo-ku, Tokyo, Japan) was used as an analytical control to monitor the reproducibility and accuracy of the amino acid determinations. Amino acids in the hydrolysate were separated using cation-exchange column chromatography with post-column derivatisation with O-phthaldialdehyde (Sigma Chemicals Co., St Louis, MO, USA) and fluorometric detection. Tryptophan was not determined.

Calculations

Apparent ileal digestibility coefficients of CP and amino acids were calculated using the AIA as a marker as follows:

Apparent ileal amino acid digestibility coefficients = \frac{(AA / AIA) d - (AA / AIA) i}{(AA / AIA) d}

where (AA/AIA)d = ratio of amino acid to AIA in diet, and (AA/AIA)i = ratio of amino acid to AIA in ileal digesta.

Statistical analyses

General linear model and Minitab program (ver. 16.0, Minitab Pty Ltd, Sydney, NSW, Australia) were used to analyse the data (Steele et al. 1997). Pearson correlation coefficients (r) were calculated and linear regression techniques were used to determine the relationship of CP content with amino acid and digestible amino acid contents. The significance was declared at P < 0.05.

Results and discussion

The CP contents of expeller- and solvent-extracted canola meals distinctly differed, but both categories were considered together in the statistical analysis because of the small number of expeller samples (Table 1). A description of the processing and oil extraction of canola in Australia has been provided by Spragg and Mailer (2007). The mean, minimum, maximum and standard deviation of CP and amino acid contents of the 13 canola meal samples are shown in Table 2. The CP content ranged from 277 to 394 g/kg, with a mean value of 344 g/kg. The amino acid contents also varied greatly; for example, the range of values for lysine was 17.0–20.7. The data showed that the amino acid profile of canola meal is reasonably well balanced. The CP and amino acid contents of the canola meal samples were within the range reported in the literature (Bell and Keith 1991; Spragg and Mailer 2007; Wiltafsky et al. 2016). The observed variability may be explained inter alia by differences in genotype/cultivar, geographical location, growing season, agronomic practices, environmental conditions during crop growth and harvest (Spragg and Mailer 2007; Adewole et al. 2016). Protein and amino acid contents can vary from season to season, with dry conditions producing low oil and high protein contents (Spragg and Mailer 2007; Newkirk 2011). In addition, the processing method could influence the protein and amino acid contents of the meal. It has been reported in Australia (Spragg and Mailer 2007) and Canada (Bell and Keith 1991; Adewole et al. 2016), that different crushing plants produce canola meals differing in composition, as was also evident in this study

Table 2.Crude protein and amino acid contents (g/kg, air-dry basis) of canola meal.

Item	Mean	Minimum	Maximum	Standard deviation
Crude protein	344	277	394	38.2
Alanine	15.3	12.5	17.8	1.69
Arginine	21.1	16.6	24.9	2.58
Aspartic acid	24.6	20.0	28.3	2.49
Glutamic acid	61.9	48.7	71.6	8.12
Glycine	17.5	15.1	20	1.80
Histidine	10.7	8.6	13.1	1.24
Isoleucine	14.4	12.7	16.5	1.44
Leucine	24.7	20.9	28.4	2.67
Lysine	20.7	17.0	23.7	1.90
Methionine	4.9	3.7	6.0	0.83
Phenylalanine	14.0	12.0	15.9	1.31
Serine	15.3	9.7	18.7	3.44
Threonine	15.4	12.0	17.7	1.94
Tyrosine	10.8	9.8	12.0	0.75
Valine	18.3	16.1	21.5	1.95

Number of samples = 13.

The ileal protein and amino acid digestibilities of canola meal were lower and more variable (Table 3) than those reported for soybean meal (Ravindran et al. 2005; Khajali and Slominski 2012; Barua et al. 2024). The protein digestibility coefficients varied widely from 0.66 to 0.81. The ranges for lysine and threonine digestibility coefficients were 0.64–0.84 and 0.51–0.75 respectively. The variations observed in the apparent ileal digestibility for broilers in the current study were as expected, with Li et al. (2002) and Fan et al. (1996) reporting similar findings with pigs. The variations primarily reflect differences in processing conditions during oil removal and production of the meal. Thermal treatment is an integral part of the processing of oilseeds. Heat is generated during expeller extraction, whereas distillation is applied during solvent extraction to remove the solvent and to inactivate the anti-nutritional factors. However, the extent of negative effects of thermal treatment on the quality of the residual meal are determined by the temperature, time, moisture and reducing sugar content (Lund and Ray 2017). Excessive heat was found to reduce the lysine content, protein solubility (Jensen et al. 1995) and the digestibility of amino acids in canola meal for poultry (Anderson-Hafermann et al. 1993; Toghyani et al. 2015) and pigs (Almeida et al. 2014; Oliveira et al. 2020). Differences in the type and content of anti-nutritional factors could also contribute to the observed variation in digestibility, and these include tannins (Spragg and Mailer 2007), fibre (Toghyani et al. 2015) and phytate (Moss et al. 2018).

Table 3.Apparent ileal crude protein and amino acid digestibility coefficients of canola meals.

Item	Mean	Minimum	Maximum	Standard deviation
Crude protein	0.75	0.66	0.81	0.04
Alanine	0.77	0.63	0.84	0.05
Arginine	0.83	0.74	0.89	0.04
Aspartic acid	0.73	0.60	0.82	0.06
Glutamic acid	0.84	0.80	0.89	0.04
Glycine	0.76	0.65	0.90	0.06
Histidine	0.78	0.68	0.82	0.04
Isoleucine	0.75	0.61	0.81	0.05
Leucine	0.78	0.67	0.85	0.04
Lysine	0.77	0.64	0.84	0.05
Methionine	0.90	0.85	0.93	0.02
Phenylalanine	0.79	0.73	0.85	0.03
Serine	0.70	0.58	0.78	0.05
Threonine	0.67	0.51	0.75	0.06
Tyrosine	0.76	0.68	0.81	0.04
Valine	0.73	0.58	0.80	0.05

Number of samples = 13.

The range of values for digestible protein and amino acid contents of the 13 canola meal samples are presented in Table 4. There were significant (P < 0.05–0.001) correlations between CP and amino acid contents (Table 5); the only exception was serine content (P = 0.11). The correlation coefficients of CP and amino acid contents were >0.80 for most amino acids, except histidine (r = 0.56), isoleucine (r = 0.78), lysine (r = 0.62) and serine (r = 0.43). Such a strong correlation between CP and amino acid contents indicates that the contents of most amino acids can be predicted by analysing the CP content of canola meal.

Table 4.Intercept, slope and correlation coefficients of regression lines describing amino acid content (g/kg) as a function of crude protein content (g/kg) in canola meals.

Amino acid	Intercept (a) (±s.e.)	Slope (b) (±s.e.)	Correlation coefficient (r)	P-value
Alanine	1.19 (±1.74)	0.040 (±0.0005)	0.93	<0.001
Arginine	0.19 (±3.02)	0.061 (±0.009)	0.91	<0.001
Aspartic acid	4.65 (±3.10)	0.058 (±0.009)	0.90	<0.001
Glutamic acid	−8.18 (±6.19)	0.204 (±0.018)	0.96	<0.001
Glycine	3.40 (±2.43)	0.041 (±0.007)	0.87	<0.001
Histidine	3.62 (±2.61)	0.021 (±0.008)	0.64	0.019
Isoleucine	5.10 (±2.73)	0.027 (±0.008)	0.72	0.006
Leucine	2.32 (±2.59)	0.065 (±0.007)	0.93	<0.001
Lysine	10.07 (±4.07)	0.031 (±0.012)	0.62	0.024
Methionine	−1.37 (±1.23)	0.018 (±0.004)	0.84	<0.001
Phenylalanine	3.66 (±1.76)	0.030 (±0.005)	0.87	<0.001
Serine	0.85 (±8.29)	0.042 (±0.024)	0.47	0.107
Threonine	1.76 (±3.28)	0.040 (±0.01)	0.78	0.002
Tyrosine	5.78 (±1.35)	0.015 (±0.004)	0.75	0.003
Valine	5.34 (±3.58)	0.038 (±0.010)	0.74	0.004

Y = a + bX, where Y = amino acid content (g/kg) and X = crude protein content (g/kg). Number of samples = 13.

Table 5.Apparent ileal digestible crude protein and amino acid contents (g/kg, air-dry basis) of canola meals.

Item	Mean	Minimum	Maximum	Standard deviation
Crude protein	261.8	188.1	307.0	34.40
Alanine	11.8	9.3	13.8	1.68
Arginine	17.6	12.8	21.6	2.77
Aspartic acid	17.9	13.4	21.6	2.50
Glutamic acid	51.8	39.0	62.6	6.94
Glycine	13.4	10.7	15.5	1.83
Histidine	8.3	6.5	10.1	1.03
Isoleucine	10.8	7.3	13.0	1.64
Leucine	19.4	15.5	23.1	2.79
Lysine	15.9	12.1	18.7	2.22
Methionine	4.4	3.2	5.5	0.77
Phenylalanine	11.0	9.0	12.7	1.26
Serine	10.6	6.3	14.2	2.38
Threonine	10.3	7.7	13.1	1.63
Tyrosine	8.2	7.0	9.5	0.82
Valine	13.5	9.3	16.8	2.12

Ileal digestible protein/amino acid content (g/kg) = protein/amino acid content (g/kg) × ileal digestibility coefficient. Number of samples = 13.

The range of values for the ileal digestible protein and amino acid contents of the 13 canola meal samples are summarised in Table 5. Significant correlations between the CP content and ileal digestible contents were observed for most of amino acids (Table 6) with coefficients of >0.80 (P < 0.05–0.001). Lower correlation coefficients were found for lysine (r = 0.48; P = 0.11) and serine (r = 0.55; P = 0.06). The poor correlation for lysine may be attributed to its susceptibility to destruction during processing (Newkirk et al. 2003), perhaps owing to heat or the Maillard reaction because lysine has an ε-amino group that can react directly with reducing sugars under hot and moist conditions (Lund and Ray 2017). Moreover, the apparent digestibility of lysine in canola was reported to decrease by 5–8% during the solvent extraction process (Anderson-Hafermann et al. 1993; Newkirk et al. 2003).

Table 6.Intercept, slope and correlation coefficients of regression lines describing ileal digestible amino acid content (g/kg) as a function of crude protein content (g/kg) in canola meals.

Amino acid	Intercept (a) (±s.e.)	Slope (b) (±s.e.)	Correlation coefficient	P-value
Alanine	−0.58 (±1.49)	0.037 (±0.004)	0.94	<0.001
Arginine	−2.61 (±3.36)	0.060 (±0.010)	0.89	<0.001
Aspartic acid	2.90 (±3.76)	0.045 (±0.011)	0.79	0.002
Glutamic acid	−2.28 (±8.84)	0.159 (±0.026)	0.89	<0.001
Glycine	−1.05 (±1.43)	0.043 (±0.004)	0.96	<0.001
Histidine	3.17 (±2.14)	0.015 (±0.006)	0.62	0.032
Isoleucine	1.74 (±1.97)	0.027 (±0.006)	0.84	<0.001
Leucine	−1.73 (±2.72)	0.062 (±0.008)	0.93	<0.001
Lysine	7.75 (±4.90)	0.025 (±0.014)	0.48	0.112
Methionine	−1.21 (±1.19)	0.016 (±0.003)	0.83	<0.001
Phenylalanine	0.91 (±1.53)	0.030 (±0.004)	0.90	<0.001
Serine	−1.12 (±5.70)	0.034 (±0.016)	0.55	0.065
Threonine	−0.14 (±2.28)	0.031 (±0.007)	0.83	<0.001
Tyrosine	2.54 (±1.35)	0.017 (±0.004)	0.80	0.002
Valine	1.30 (±2.88)	0.036 (±0.008)	0.81	0.001

Y = a + bX, where Y = digestible amino acid content (g/kg) and X = crude protein content (g/kg). Number of samples = 13.

The accepted method of measuring the digestible amino acid contents in feedstuffs for broilers is using in vivo assays and chromatographic analysis, but these are costly and time-consuming. It is therefore of interest to find rapid and inexpensive methods for assessing digestible amino acid contents of feedstuffs. The regression equations reported herein show that CP content can be used to predict digestible amino acid contents of canola meal, although equations for lysine, serine and histidine should be treated with caution.

In conclusion, a limited number of samples was tested in this study. To improve the reliability of prediction equations, a greater number of samples is required from different seasons, growing locations and processing procedures. Nevertheless, the strong correlation coefficients determined in this study indicated that apparent ileal amino acid content can be derived from the CP content of canola meal.

Data availability

Data will be made available upon reasonable request to the corresponding author.

Conflicts of interest

W. L. B. is a member of the Editorial Board of Animal Production Science. To mitigate this potential conflict of interest they had no editor-level access to this manuscript during peer review. The authors have no further conflicts of interest to declare.

Declaration of funding

This study was supported by the Chicken Meat Programme of the RIRDC and the School of Agriculture and Food Sustainability, the University of Queensland.

Acknowledgements

We acknowledge the assistance of the postgraduate students in the conduct of digestibility assays.

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