Prof Velmurugu Ravindran Massey University, New Zealand

Transcription

1 Prof Velmurugu Ravindran Massey University, New Zealand Digestible amino acids in feedstuffs for poultry Sponsored by:

2 Ileal Digestible Amino acids in Feedstuffs for Poultry V. Ravindran Massey University Palmerston North, New Zealand

3 Apparent ileal lysine digestibility

4 Australasian Situation

5 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

6 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

7 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

8 First set of trials Comparison of ileal vs. excreta digestibility for a range of ingredients

9 Ileal measurements Effects of hindgut microbes on undigested protein Contribution of microbial proteins to excreta amino acids Contribution of urinary AA

10 Ileal vs. excreta digestibility Maize Arg His Ile Leu Lys Met Phe Thr Val Ileal Excreta

11 Wheat Arg His Ile Leu Lys Met Phe Thr Val Ileal Excreta

12 Meat and bone meal Arg His Ile Leu Lys Met Phe Thr Val Ileal Excreta

13 Site of digesta collection

14

15 N digestibility over the GI tract

16 N digestibility in three ileal sub-sections (Kluth et al., 2005)

17 Assay diets Direct method Difference method Regression method

18 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

19 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 % Vitamins, trace minerals 1.0% 1.0% 1.0%* Marker (AIA/ TiO 2 ) + + +

20 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)

21 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

22 Suggested methodology

23 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

24 True vs. apparent digestibility

25 True Digestibility Amino Acid Digestibility (%) 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

26 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

27 Measurement of endogenous losses

28 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

29 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)

30 Standardization of apparent digestibility values

31 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)

32 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.

33 Apparent Ileal Amino Acid Digestibility (%) Obs CP Met Met+ Cys Lys Thr Trp Arg Corn Wheat Sorghum Soybean meal Canola meal Cottonseed meal Meat and bone meal

34 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

35 Animal protein sources Blood meal > fish meal >> MBM, feather meal Wide variations Cys was the least digestible AA Except in blood meal - Ile

36 Other issues of interest Effect of age of broilers Huang et al Brit Poult Sci. 46: feed ingredients - 14, 28 and 42 days of age

37 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

38 Combined effects on all ingredients Lys Meth Thr Ile 14 d 28 d 42 d

39 Newly hatched chick Protein digestion is compromised during week 1

40 Ileal N digestibility Corn/soy diets Day 3 Day 5 Day 7 Day 14

41 AME data AME, MJ/kg DM Day Wheat-soy Corn-soy

42 Influence of bird type Broilers vs. Layers Huang et al Poult. Sci. 85: 625 Huang et al J. Sci. Food Agric. 87:

43 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

44 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