Prof Velmurugu Ravindran Massey University, New Zealand Digestible amino acids in feedstuffs for poultry Sponsored by:
Ileal Digestible Amino acids in Feedstuffs for Poultry V. Ravindran Massey University Palmerston North, New Zealand
Apparent ileal lysine digestibility
Australasian Situation
Typical diets are complex and based on range of less digestible ingredients Industry has always been interested in formulating diets based on digestible AA But considerable confusion about terminology Excreta vs. Ileal True vs. apparent Rooster vs. broiler
Survey of AA digestibility of local ingredients Growing birds, not adult birds Confirm that ileal digestibility provides an advantage Develop a procedure for ileal digestibility assay Start a well-planned survey
OUTLINE Ileal vs. excreta digestibility Overview of suggested methodology Apparent vs. true digestibility Concept of standardizing digestibility values Ileal digestibility estimates of common ingredients Animal factors influencing AA digestibility Conclusions
First set of trials Comparison of ileal vs. excreta digestibility for a range of ingredients
Ileal measurements Effects of hindgut microbes on undigested protein Contribution of microbial proteins to excreta amino acids Contribution of urinary AA
Ileal vs. excreta digestibility Maize 95 85 75 65 55 Arg His Ile Leu Lys Met Phe Thr Val Ileal Excreta
Wheat 90 80 70 60 50 Arg His Ile Leu Lys Met Phe Thr Val Ileal Excreta
Meat and bone meal 90 80 70 60 50 Arg His Ile Leu Lys Met Phe Thr Val Ileal Excreta
Site of digesta collection
N digestibility over the GI tract
N digestibility in three ileal sub-sections (Kluth et al., 2005)
Assay diets Direct method Difference method Regression method
Direct method Test ingredient as the only source of AA To supply around 18% of protein in the diet Semi-purified diet; starch or dextrose as energy source; fortified with minerals and vitamins
Typical composition of test diets Grains Plant Animal byprotein sources products Test substance 91.8% to achieve 18% CP Dextrose/ starch - depends on test substance Vegetable oil 2.0% 6.0% 2.0% Dical phosphate 1.7% 1.9% - Limestone 1.3% 1.0% - Salt 0.2% 0.2% 0.2% Cellulose - - 3.0% Vitamins, trace minerals 1.0% 1.0% 1.0%* Marker (AIA/ TiO 2 ) + + +
Limitations of direct method Assay diets will have high levels of test ingredient for low/ moderate-protein meals Cereals (Corn/ wheat) > 90% Legumes (Peas/ lupins) 50-70% Underestimation of digestibility estimates (due to high proportion of endogenous AA in the digesta)
Difference method A basal diet and a test diet are formulated Test diet will contain a mixture of basal diet and the test ingredient (50:50) Digestibility is measured by differences between the two diets and contribution of AA from test ingredient to the test diet Limitation: assumes that there is no interaction
Suggested methodology
At least 4 replicates per ingredient No of birds per replicate depends on the age of birds and amount of digesta needed Age of birds Assay diet direct method preferred Use appropriate method of euthanasia Site of collection Flush digesta using distilled water Freeze-dry
True vs. apparent digestibility
True Digestibility Amino Acid Digestibility (%) 100 95 90 85 80 75 70 True/ standardized coefficients are independent of AA intake The relative contribution from endogenous sources to total AA excretion decreases with increasing AA intake Dietary Amino Acid Intake
Apparent digestible values Underestimation of digestibility in low-protein ingredients Question of additivity in practical diets BUT apparent digestible amino acid contents are likely to be additive True/ standardized values Reliability of methods to measure endogenous losses under a given dietary condition
Measurement of endogenous losses
Recovery of AA at the distal ileum Endogenous losses Significant losses of endogenous amino acids occur during digestion in the gut. Endogenous AA originate from digestive secretions, mucin and epithelial cells non-digested dietary AA ingredient specific AA losses Non-specific (basal) AA losses* Dietary protein or amino acid intake
Accurate estimation is needed Fasting N-free diet Regression Highly digestible proteins (casein, wheat gluten) at 10% inclusion Enzyme hydrolysed casein Guanidinated proteins Isotope-dilution method ( 15 N)
Standardization of apparent digestibility values
Standardised ileal digestibility values Standardising apparent ileal values by correcting for basal endogenous losses Basal losses represent the minimal loss of endogenous AA and are independent of diet/ ingredient composition = adc (%) + { Basal EAA (g/kg DMI) } x 100 AA of ing (g/kg DM)
Standardised ileal digestibility values Apparent digestibility and endogenous losses need not be determined in the same experiment. Published apparent ileal digestibility values can be transformed to standardised values.
Apparent Ileal Amino Acid Digestibility (%) Obs CP Met Met+ Cys Lys Thr Trp Arg Corn 12 80 90 83 83 68 70 88 Wheat 38 80 88 87 79 73 81 81 Sorghum 22 77 85 78 79 67 81 83 Soybean meal Canola meal Cottonseed meal Meat and bone meal 26 88 90 84 89 82 88 93 12 79 83 79 79 70 78 87 4 76 71 71 63 64 79 87 41 63 71 60 68 59 53 76
Cereals Corn, wheat > sorghum, triticale, barley But variation within cereals > between cereals Thr and lys were the least digestible essential AA Wheat middlings > rice polishings Plant protein sources SBM, sunflower > canola > cottonseed Lupins = SBM >> peas Thr was the least digestible essential AA Except in cottonseed meal - lys
Animal protein sources Blood meal > fish meal >> MBM, feather meal Wide variations Cys was the least digestible AA Except in blood meal - Ile
Other issues of interest Effect of age of broilers Huang et al. 2005. Brit Poult Sci. 46: 236-245 - 8 feed ingredients - 14, 28 and 42 days of age
Effect of age of broilers Digestibility was generally lower at 14 d In general, increased with age (but small increases) Effect of age varied with ingredients Wheat, corn, CM, SBM, MBM (42=28, but different from 14) Wheat middlings, 42 >28=14 Cottonseed meal, 42=28=14
Combined effects on all ingredients 85 80 75 70 65 60 Lys Meth Thr Ile 14 d 28 d 42 d
Newly hatched chick Protein digestion is compromised during week 1
Ileal N digestibility Corn/soy diets 90 85 80 75 70 65 60 Day 3 Day 5 Day 7 Day 14
AME data AME, MJ/kg DM 16 15 14 13 12 11 10 2 4 6 8 10 14 21 Day Wheat-soy Corn-soy
Influence of bird type Broilers vs. Layers Huang et al. 2006. Poult. Sci. 85: 625 Huang et al. 2006. J. Sci. Food Agric. 87: 47-53.
Future Research AA digestibility data for common ingredients generated with growing birds Effect of age and gender Relevance of rooster values to growing birds? Reliable values for basal endogenous amino acid losses
Conclusions Debate regarding the most appropriate ways to measure and describe amino acid digestibility will continue Standardised ileal digestibility values, determined with growing birds, should be considered