A Comparison of Total & Digestible Amino Acids in Diets for Broilers and Layers

Transcription

1 A Comparison of Total & Digestible Amino Acids in Diets for Broilers and Layers A report for the Rural Industries Research and Development Corporation By David J. Farrell August 2000 RIRDC Publication No 98/124 RIRDC Project No UQ-52A

2 2000 Rural Industries Research and Development Corporation. All rights reserved. ISBN ISSN A Comparison of Total and Digestible Amino Acids in Diets for Broilers and Layers Publication No. 98/124 Project No. UQ-52A The views expressed and the conclusions reached in this publication are those of the author and not necessarily those of persons consulted. RIRDC shall not be responsible in any way whatsoever to any person who relies in whole or in part on the contents of this report. This publication is copyright. However, RIRDC encourages wide dissemination of its research, providing the Corporation is clearly acknowledged. For any other enquiries concerning reproduction, contact the Publications Manager on phone Researcher Contact Details David J. Farrell Queensland Poultry Research and Development Centre PO Box 327 CLEVELAND QLD 4163 Phone: Fax: farreld@dpi.qld.gov.au RIRDC Contact Details Rural Industries Research and Development Corporation Level 1, AMA House 42 Macquarie Street BARTON ACT 2600 PO Box 4776 KINGSTON ACT 2604 Phone: Fax: rirdc@rirdc.gov.au Website: Published in August 2000 Printed on environmentally friendly paper by Canprint

3 Foreword There has for many years been much discussion concerning the merits of formulating diets on the basis of digestible versus total amino acids in feedstuffs. A major problem has been the method of measurement. There are several methods and all are open to criticism. Industry has been making some adjustment to account for differences in the digestibility of the amino acids in different feedstuffs based on research and experience in diet formulation. The outcome of the research reported here should offer a practical guide for such adjustment. This project was funded from industry revenue which is matched by funds provided by the Federal Government and is an addition to RIRDC s diverse range of over 500 research publications, forms part of our Chicken Meat R&D program, which aims to support increased sustainability and profitability in the chicken meat industry by focusing research and development on those areas that will enable the industry to become more efficient and globally competitive and that will assist in the development of good industry and product images. Most of our publications are available for viewing, downloading or purchasing online through our website: downloads at purchases at Peter Core Managing Director Rural Industries Research and Development Corporation iii

4 Acknowledgment The success of this project stems largely from the dedication of the scientific, technical and farm staff at QPRDC. It is not generally recognised that dedication and hard work are the essential ingredients for satisfactory research outcomes. We thank Rhone- Poulenc Animal Nutrition, Commentry, France for their contribution to this study, in particular Dr David Jackson and Mr Theo van Kempen who coordinated the analyses and amino acid measurements. iv

5 Contents FOREWORD...III ACKNOWLEDGMENT... IV CONTENTS...ERROR! BOOKMARK NOT DEFINED. EXECUTIVE SUMMARY... VI INTRODUCTION... 1 MATERIALS AND METHODS... 2 BIOASSAYS AND CHEMICAL ANALYSES... 2 LAYER EXPERIMENTS... 2 BROILER EXPERIMENTS... 4 RESULTS... 7 LAYER EXPERIMENTS BROILER GROWTH EXPERIMENT THREONINE REQUIREMENTS OF BROILERS TO 24D DISCUSSION IMPLICATIONS RECOMMENDATIONS COMMUNICATIONS/STRATEGY...ERROR! BOOKMARK NOT DEFINED. REFERENCES ATTACHMENT 2 COMPENDIUM SUMMARY v

6 Executive Summary There has been a prodigious research effort over the years into the measurement of the amino acid digestibility of various feedstuffs using a variety of methods. Despite this, industry has been reluctant to use values because of disagreement about methodology and often conflicting results. There are few laboratories that have produced a suitable number of measurements using the one method. In this series of experiments undertaken at the Queensland Poultry Research and Development Centre (QPRDC) with layers and broilers, we first undertook detailed analyses, including apparent metabolisable energy and amino acid total and digestible measurements, of 11 foodstuffs; two of these were grains and the remainder protein concentrates. In the two layer experiments, we used 25 or 50 individually-caged young Isabrown hens per treatment. In experiment 1, diets were formulated to either 100% or 85% of nutrient specifications expected to support good egg production on a total or digestible amino acid basis. The ingredients were arbitrarily divided into two groups (group 1 and 2) and there were formulations undertaken within each group. There were eight dietary treatments. The experiment ran for 20 weeks. In the second layer experiment, there were four formulations. These were based on 97% and 90% of nutrient specifications for total and digestible amino acids. The experiment ran for 20 weeks. The purpose of the first broiler trial was to determine the biological responses of broilers during the starter and finisher phase to diets based on 100%, 97%, 94% and 91% of total and digestible amino acid specifications expected to support a high rate of growth. There were four groups of 40 males and four groups of 40 females per dietary treatment. The objective of the second experiment was to determine the threonine requirements of starter chicks and compare the biological responses to varying intakes of total or digestible threonine using the 11 feedstuffs on which detailed analyses were undertaken. The amino acid analysis gave relatively small differences in amino acid digestibility coefficients for most ingredients. Two exceptions were cottonseed meal and one meat and bone meal A (60% CP) for digestible lysine in particular. AME values for all ingredients were similar to those published. The results of the first layer experiment showed no difference in any parameter between total and digestible amino acids in group 1 except that food intake was lower (P<0.05) in the digestible amino acid formulation. In group 2, the total amino acid 100% formulation gave lower (P<0.05) hen-day production and egg mass than the corresponding digestible formulation. The 85% formulations gave lower outputs for hen-day egg production and often egg mass than their counterpart 100% treatments. The digestible amino acid 85% group 2 gave very poor overall performance. Amino acid profile of this diet indicated that lysine was well below specifications but this was not so for the corresponding diet formulated from group 1 ingredients. vi

7 In the second experiment, there were no differences (P>0.05) in any parameter between any of the treatments. Egg production was consistently high over the 20 weeks of the experiment (87.3% - 91%) and food conversion ratio (FCR) was In the broiler growth experiment, there were no differences in final bodyweights and FCR on any of the eight treatments nor any diet x treatment interactions. At 21 d of age there was a reduction (P<0.05) in FCR as formulations declined from 100 to 91% of requirements but only in diets formulated on a total but not on a digestible amino acid basis. Generally these formulations gave better FCRs than their corresponding digestible amino acid formulations. In the experiment designed to determine threonine requirements of starter broilers six diets were formulated from well below to above threonine requirements using a diet dilution technique. Based on growth rate, the total digestible threonine requirement (g/kg) was 7.8 and that for threonine was 6.7; using FCR as the criterion, corresponding values were 8.6 and 7.2 respectively. vii

8 Introduction It has been known for many years that not all of the amino acids in a feedingstuff are digested by the bird and then available for protein synthesis. It is also known that there is considerable variation between, and often within, protein sources in the digestibility of amino acids. Furthermore the digestibility coefficient of individual amino acids within a feedstuff may differ considerably. The methods used to measure amino acid digestibility vary considerably and these have been reviewed on numerous occasions (see Sibbald, 1987; Johnson, 1992; McNab, 1995). Site of sampling is important and the indigestible marker used to calculate ileal digestibility may also vary between laboratories. There has been some criticism of the use of excreta in order to determine amino acid digestibility because of changes in amino acid profile due to microbial fermentation (Terpstra, 1997; Low, 1977) even in caecectomized birds (Yaharjo and Farrell, 1984). However there are few tables that provide information on digestible amino acids of a wide range of feedstuffs using the same method and from the one laboratory. There are, however, notable exceptions (Anonymous, 1989; Ravindran et al. 1998). There has been a number of papers demonstrating the advantages of using digestible, rather than total, amino acids to formulate broiler diets. These have generally used poor quality ingredients in large amounts, such as cottonseed meal (Fernandez et al., 1995) to demonstrate an advantage. There are very few papers that have demonstrated a significant improvement in diets for layers and for broilers formulated on the basis of digestible amino acids when several ingredients have been combined. The purpose of the first three experiments reported here was to test the hypothesis that the use of amino acid digestibility values of feedstuffs gives a significant improvement in biological response and/or economic response compared to ingredients using total amino acids to formulate layer and broiler diets. Because of the detailed analyses of the 11 raw ingredients, the opportunity was taken to determine the total and digestible threonine requirements of broiler chicks during the starter phase with some of the ingredients that were surplus to requirements. Based on current estimates of amino acid requirements, threonine is often the third limiting essential amino acid after methionine and lysine in typical Australian diets for broiler chickens. The requirement for threonine is often most cheaply met by its direct addition to the diet but the current cost of manufactured threonine is considerably greater than that of either lysine or methionine. There are no published data comparing responses of broilers to intakes of total and digestible threonine from diets based solely on Australian foodstuffs and from which estimates of requirements can be made. We examined this here with broilers grown to 24 d of age. 1

9 Materials and Methods Bioassays and chemical analyses Substantial quantities of eleven food ingredients were held in silos or bags prior to use in poultry experiments. Samples (10 kg) were transported to Rhone-Poulenc Animal Nutrition, Commentry, France for bioassay using adult birds (Sibbald, 1987) with modifications (Anonymous, 1989) to determine true amino acid digestibility. Isa brown cockerels were caecetomized and five birds per treatment were used in a Latin square design (Green and Kiener, 1989). The apparent metabolisable energy (AME) of the ingredients was determined with individual laying hens using the classical, total collection method over four days. Birds were on the experimental diets for a three-day adjustment period. There were three hens per dietary treatment. The two grains were included at 98% of the diet; the protein sources replaced sorghum at two different levels; these levels depended on the ingredient. A premix, which contained minerals and vitamins, was included at 2% of the diet. AME was calculated by regression analysis and then extrapolating the line to 100% inclusion of the test ingredient. Chemical analyses of the raw ingredients followed the methods of the AOAC (1984). Layer experiments A least-cost formulation package (Feedmania) was used to construct diets using the determined amino acid and AME values for the feedstuffs. There were two experiments. The first was a preliminary experiment. Here layer diets were formulated to 100% and 85% of total or digestible amino acid requirements (SCA, 1987; Anonymous, 1989). The protein concentrates were arbitrarily divided into two groups. Each group was used to formulate least cost-diets. Thus there were eight diets in total. The ingredient and calculated chemical composition of the eight diets is given in Table 1. Each diet was fed to 25 individually-caged Isabrown laying hens aged 26 weeks and housed in a saw-toothed shed for 20 weeks. In the second layer experiment, diets were formulated to 97% and 90% of total and digestible amino acid requirements. Unlike experiment 1, there was only one set of formulations at each level giving a total of four diets. The composition of the least-cost formulated diets is given in Table 2. Each diet was fed for 20 weeks to 50 individually-caged Isabrown birds and housed as previously described In both experiments, diets were fed ad libitum in mash form. A mineral and vitamin layer premix and a yolk pigmentor were added to all layer diets at the recommended levels. Egg production was recorded on five days a week, eggs were weighed weekly, food intake recorded monthly and egg specific gravity monthly. Hens were weighed at the start and end of each experiment. 2

10 Table 1. Ingredient and calculated chemical composition (g/kg) of diets based on total (T) and digestible (D) amino acids at 100% and 85% of requirements in two formulations (1, 2) in layer experiment 1 T100-1 T100-2 D100-1 D100-2 T85-1 T85-2 D85-1 D85-2 Wheat Sorghum Cottonseed meal Faba beans Fish meal Meat & bone meal A Rapeseed meal Soybean meal Sunflower meal Sweet lupins Soybean oil Dical P Limestone Salt D-L methionine L-lysine Chemical composition (g/kg) Crude protein AME (MJ/kg) Lysine Methionine Methionine cystine Tryptophan Threonine Table 2. Ingredient and calculated chemical composition (g/kg) of diets formulated on a total (T) and digestible (D) amino acid basis at 97% and 90% of amino acid recommendations (Layer experiment 2) T-97 T-90 D-97 D-90 Sorghum Wheat Cottonseed meal Faba beans Meat & bone meal A Rapeseed Soybean oil Limestone Dical P Salt DL-Methionine Chemical composition (g/kg) Crude protein AME (MJ/kg) Lysine Methionine Methonine + cyst Tryptophan Threonine

11 Broiler experiments There were two broiler experiments. In the first, we compared diets formulated to total and digestible amino acids at 100%, 97%, 94% and 91% of nutrient requirements for starter and finisher broilers. The diets are shown in Tables 3 and 4. Chicks of a commercial strain were grown from one-day-old. There were four groups each of 40 males and four groups each of 40 females per dietary treatment. Birds were grown on the floor with wood shavings as litter. Treatments were assigned randomly in blocks of eight pens. Birds and food were weighed at 1, 21 and 42 d of age. Lighting was adjusted according to commercial practice. Mortality was recorded daily. In the second experiment, we determined total and digestible threonine requirements for broiler chickens grown from 3 to 4 d of age. Table 3. Broiler diets formulated to total (T) and digestible (D) amino acid requirements that ranged from 100% to 91% of requirement Starter formulations (g/kg) Ingredients T-100 T-97 T-94 T-91 D-100 D-97 D-94 D-91 Wheat Sorghum Cottonseed meal Fish meal Meat & bone meal A Meat & bone meal B Soybean meal Sunflower meal Sweet lupins Sunflower oil Limestone Salt Vitamin premix DL-Methionine L-Lysine Chemical composition (g/kg) Crude protein AME (MJ/kg) Lysine Methionine Meth + cyst Tryptophan Threonine

12 Table 4. Broiler diets formulated to total (T) and digestible (D) amino acid requirements that range from 100% to 91% of requirements Ingredients Finisher formulations (g/kg) T-100 T-97 T-94 T-91 D-100 D-97 D-94 D-91 Wheat Sorghum Cottonseed meal Fish meal Meat & bone meal (B) Meat & bone meal (A) Soybean meal Sunflower meal Sweet lupins Sunflower oil Limestone Salt Vit + Min premix DL-methionine L-lysine Chemical composition (g/kg) AME (MJ/kg) crude protein Lysine Methionine Meth + cyst Tryptophan Threonine Data were analysed using a computer package (SAS, SAS Institute, 1985) appropriate for a completely randomised block design. Means were separated using the least significant difference test (Steel and Torrie, 1960). There were 12 experimental diets comprising two series each of six diets. The two series were based on formulations using total and digestible amino acid contents of the dietary ingredients. Within each series a range of threonine contents was obtained by blending a summit diet with a low protein dilution mixture in appropriate proportions to give five diets. The summit diet (diet 1) of each series had a threonine content that was 1.2 times the requirement estimated for maximum growth; the other essential amino acids were no less than 1.4 times requirement. The sixth diet in each series was produced by adding sufficient synthetic L-threonine to the diet with the lowest threonine (diet 5) to raise its threonine content to that of the next highest diet in the series. The dilution mixture was formulated to contain the same calcium, phosphorus and calculated metabolisable energy content as the summit diets. The composition of the two summit diets and of the dilution mixture are given in Table 5. 5

13 Table 5. The ingredient composition (g/kg) of the summit diets for total (TAA) and digestible (DAA) amino acids and the dilution mixture for the threonine bioassay Summit TAA Summit DAA Dilution Sorghum Soybean meal Cottonseed meal Meat and bone meal B Fishmeal 28.3 Faba beans 58.7 Ground rice husks Starch Sucrose Soybean oil Limestone Dicalcium phosphate Sodium chloride Ferrous sulphate 1.6 DL-methionine L-lysine HC L-isoleucine L-leucine 1.3 L-histidine 0.5 L-valine Mineral premix Vitamin premix There were 96 experimental cages, enabling the 12 dietary treatments, applied to two sexes, to be randomly allocated within four positional replicates in a randomized block layout. Broiler chickens, obtained from a commercial hatchery which had been vent sexed and vaccinated for IB, were reared in wire cages in a heated room from one-day-old. At three days of age chickens within each sex were individually weighed and assigned to groups, each with a weight range of 5 g. The heaviest and lightest were discarded and the remainder were randomly assembled into groups of eight chickens, such that each group had a liveweight of similar mean and variance. Each group was housed in a wire cage until the completion of the experiment at 24 days of age. Food and water were available ad libitum. Illumination was for 23 h and hot-air brooders provided heating and ventilation. The temperature of the experimental rooms was regulated thermostatically in accordance with the comfort of the birds (30 o to 23 o C). Food intake and liveweight were measured after 21 d on the experimental diets. Birds which died were individually weighed and the food residue recorded at that time in the affected cage. 6

14 Results The proximate analysis of the 11 ingredients used is given in Table 6, and their amino acid profiles in Table 7. The two meat and bone meals contained 53.5% crude protein (A), and 59.6 (B) on an 'as is' basis The true digestibility of the amino acids in each ingredient is given in Table 8. The two meat meals showed considerable differences in amino acid digestibility coefficients. Cotton seed meal had the lowest lysine digestibility of 60%, followed by meat meal B of 78%. The apparent metabolisable energy of eight of the 11 ingredients is given in Table 9. All compare favourably with those reported in the literature. AME values for sweet lupins and faba beans were taken from a previous study (Perez-Maldonado et al. 1998). Table 6. Proximate analysis of feed ingredients on an as fed basis (g/kg) Crude protein Dry matter Ash Fat Crude fibre Cotton seed meal Soybean meal Sorghum Lupins Faba beans Sunflower meal Rapeseed Wheat Meat & bone meal A nd Meat & bone meal B nd Fish meal nd 1 Urease activity: 0.11 mg N (from ammonia)/(g*min) 2 Ca=73.3, Phos= Ca=86.6, Phos= Ca=33.7, Phos=22.4 7

15 Table 7. Amino acid content of feed ingredients on an as fed basis (g/kg) CSM 1 SBM 2 Sorg 3 Lup 4 Fab 5 SF 6 Rap 7 Wh 8 MBA 9 MBB 10 FM 11 Asp Thr Ser Glu Pro Gly Ala Cys Val Met Ile Leu Tyr Phe Lys His Arg Try CSM = cottonseed meal, 2 SBM = soybean meal, 3 Sorg = grain sorghum, 4 Lup = sweet lupins, 5 Fab = faba beans, 6 SF = sunflower meal 7 Rap -= Rapeseed meal, 8 Wh = Wheat, 9 MBA = meat and bone meal A, 10 MBB = meat and bone meal B, 11 FM = fish meal 8

16 Table 8. True digestibility (%) of protein and amino acids in 11 feed ingredients measured using adult caecetomised cockerels CSM SBM Sorg Lup Fab SF Rap Wh MA54 MB60 FM Protein Asp Thr Ser Glu Pro Gly Ala Val Ile Leu Tyr Phe Lys His Arg Cys Met Try

17 Table 9. The apparent metabolisable energy (MJ/kg DM) of nine ingredients Cottonseed meal 7.21 Fish meal Meat & bone meal A Meat & bone meal B Rapeseed (full fat) Sunflower meal (33%) 7.18 Soybean meal Sorghum Wheat Layer experiments Production data for experiment 1 are given in Table 10. Bodyweight change of birds over the 20 week period was least on the four diets formulated to only 85% of amino acid specifications. Diets formulated to 100% of specifications on a digestible amino acid basis maintained average egg production of >90%. This was also seen for the total digestible formulation 1. Those diets formulated to 85% of amino acid requirements showed lower egg production and generally lower egg mass. Egg mass was higher (P<0.05) on diets formulated to 100% of digestible amino acids and 100% of total amino acids except for 100% of total 2. The diet formulated to 85% of digestible amino acids (2) gave inferior (P<0.05) production and egg mass compared to other diets, reflecting the low food intake of 95 g/d per bird. Food conversion ratio was poorer for birds on diets formulated to 85% of digestible amino acid specifications. Because of the unusually poor performance of the 85% digestible amino acid diet (2), amino acid analysis was undertaken on this diet and that of 85% digestible amino acid (1) for comparison. The results are given in Table 11. Although these diets were calculated to contain 15% and 16% crude protein, the values in Table 10 are 17.7% and 17.3% for D85-1 and D85-2 respectively. Total lysine of 0.61 and only 0.53 would probably explain the difference in performance. All other important amino acids were similar in the two formulations. 10

18 Table 10. Egg production, egg weight, egg mass, food intake and food conversion ratio, and specific gravity are given for each of the eight diets (Layer experiment 1) 1 Diet description Egg production (%) Egg weight (g) Egg mass (g) Food intake (g/d) Food conversion ratio (g/g) Specific gravity 100% Total AA (1) 90.5 ab 61.2 a 55.3 a a 2.19 bc ab 100% Digestible AA (1) 91.3 a 61.1 a 55.8 a bc 2.05 d b 100% Total AA (2) 86.4 bc 58.6 b 50.6 cd bc 2.19 bc ab 100% Digestible AA (2) 91.3 ab 59.5 ab 54.3 ab ab 2.12 cd ab 85% Total AA (1) 86.7 abc 58.4 bc 50.8 cd bc 2.27 ab ab 85% Digestible AA(1) 85.0 c 60.1 ab 51.1 bc bc 2.29 ab ab 85% Total AA (2) 83.9 c 56.7 cd 47.6 d c 2.30 ab ab 85% Digestible AA (2) 72.7 d 56.1 d 40.7 e 94.6 d 2.38 a a LSD P< Values with different superscripts differ significantly (P>0.05) Table 11. Total amino acid profiles (%) of the two diets formulated to 85% of digestible(d) amino acid specifications (layer experiment 1) D85-1 D85-2 Crude protein Hydroxyproline Aspartic acid Threonine Serine Glutamic acid Proline Glycine Alanine Cysteine Valine Methionine Isoleucine Leucine Tyrosine Phenylalanine Histidine Lysine Arginine Tryptophan

19 The overall results of experiment 2 show no treatment effect on any parameter (Table 12). There was some indication that the diet formulated to 90% of total amino acid requirements gave a lower egg mass by 2 g/d compared to other treatments. The diet formulated to 90% of digestible amino acids was the least expensive when only ingredient costs were considered. Table 12. Performance of birds on diets formulated to 97% and 90% of amino acid requirements on a total and digestible basis over 20 weeks (Layer experiment 2) Total Digestible P 1 97% 90% 97% 90% Egg production (%) Food intake (g/d) Egg weight (g) Egg mass (g/d) Food conversion ratio (g/g) Specific gravity Weight change (kg) Ingredient cost ($/tonne) Food cost/kg eggs ( ) Probability Broiler growth experiment The results are shown in Table 13. Since there was no diet x sex interaction, data were therefore combined for the two sexes. The only difference between dietary treatments was in FCR during the starter phase. However there was a tendency (P=0.10) for FCR to decline as the amino acid specifications declined from 100% to 91%; this was particularly so for the diet formulated to 91% of digestible amino acid requirements. FCR also tended to be worse (P = 0.071) when data were combined for total (1.40) and digestible (1.43) amino acids at 21 days of age but not at 42 days. Table 13. Bodyweight and feed conversion ratio (FCR) of broilers (sexes combined) given diets formulated on a total (T) or digestible (D) amino acid basis and to % of specifications. Bodyweight FCR Bodyweight FCR (g/bird) (g/bird) % 21 d 21 d 42 d 42 d Diet 1 T bc T c T abc T a D abc D ab D abc D a SEM

20 Threonine requirements of broilers to 24d Liveweight gain, food intake and FCR measured over the 21 d experimental period (3-24 d) and combined across sexes all responded significantly to the different dietary levels of both total and digestible threonine (Fig. 1). Interactions with sex were not significant (P>0.05). The fact that these observations represent responses to the level of dietary threonine in both the total and digestible series is supported by the significant increases (P<0.05) in liveweight gain and food intake to added L-threonine in diet 6 compared with performance on diet 5 in each series. Although the threonine content of diet 6 was the same as that of diet 4 in each diet series, performance was not the same because of restrictions imposed by the second most limiting amino acid. Diets formulated using digestible amino acids gave a significantly (P<0.05) better mean FCR than for the total amino acid series although there were no differences (P>0.05) in liveweight gain or feed intake (Fig, 2). None of the interactions were significant (P>0.05), indicating that the superior FCR for the digestible amino acid series applies over the range of dietary threonine concentration and to both male and female chicks. A quadratic model accounted for at least 98% of the variation between diets for both liveweight gain and FCR and at least 87% for food intake. The regression equations and r 2 values are given in Figure 1. Neither the linear nor quadratic coefficients of the regression equations differed (P>0.05) between the diet series for any of the parameters shown in Figure 1. Maximum liveweight gain and minimum FCR values together with their corresponding dietary threonine concentration were calculated (Table 14). These values can be compared with total threonine requirements in the range 6.3 to 7.7 g/kg reported by Kidd and Kerr (1996) for broiler chickens. Table 14. Calculated maximum liveweight gain (g/bird), minimum FCR (g/g) and corresponding dietary threonine concentration (g/kg). Data were combined across sexes Liveweight gain Dietary threonine FCR Dietary threonine TAA series DAA series To better compare the responses to both total and digestible threonine, liveweight gain and FCR were regressed on the daily intake of digestible threonine calculated for each diet in both series (Figure 2). These appear to confirm the results from the analysis of variance that formulating diets on the basis of digestible amino acids improved FCR while having no effect on liveweight gain. 13

21 Discussion There are few published experiments in which detailed chemical analysis and amino acid profiles have been constructed for as wide a range of ingredients as those used here. Although there was several months delay between the time the ingredients were dispatched to France and results received, most of the individual 14

22 Live weight gain (g/bird) Food intake (g/bird) Food conversion ratio (g/g) Y= X-25.32X 2 Y= X-26.77X 2 Y= X X r 2 r 2 = = r 2 = Digestible dietary threonine Digestible dietary threonine Digestible dietary threonine Y= X-21.05X 2 Y= X-25.32X 2 Y= X X r 2 = r 2 = r 2 = Total dietary threonine Total dietary threonine Total dietary threonine Figure 1. Fitted response curves to digestible and total dietary threonine (g/kg). 0 Response of birds fed Diet 6. Liveweight gain Food conversion Y= X r = DAA 600 TAA 500 Y= X- 2 r = Y= X E- 2 r =0.999 Y= X E- TAA DAA r = Intake digestible threonine Intake digestible threonine Figure 2. Fitted response curves for both DAA and TAA series to intake of digestible threonine. o! Response of birds fed Diet 6 of DAA or TAA series, respectively. 15

23 ingredients had not deteriorated visibly during this time. However the two grains were later replaced with grains of similar protein content for the broiler trials because of deterioration. The chemical composition and AME values were typical of each ingredient and agreed well with published data. Amino acid content and their digestibility coefficients were also generally high and similar to those reported for these ingredients. True digestibility values for almost all amino acids were high. The two exceptions were meat and bone meal B and cottonseed meal where true lysine digestibility was 78% and 60% respectively. Surprisingly, meat and bone meal B had a crude protein content of 60% (Table 6). Except for wheat, digestibility coefficients for lysine varied from 86% to 91%, and for threonine from 84% to 92%. Thus these ingredients when combined into practical least-cost formulations would produce diets with generally high and similar true amino acid digestibility values, and only about 10-15% less than total, but consistently so. It would be difficult therefore to show differences between dietary treatments particularly as amino acid requirement used are normally over-generous. Also, where requirements for total amino acids have been determined using a diet dilution technique (i.e. not dosing with synthetic amino acids) the results take account of any indigestibility of the amino acids in the experimental diets. Thus it is not surprising that one can not demonstrate a difference between formulating using total vs digestible amino acids unless ingredients of very low availability are used. A recent paper by Rostango et al. (1995) showed that there was economic benefit in formulating diets on a digestible rather than a total amino acid basis. But the benefit was not seen on the diet with highly digestible amino acids. Only when diets contained feedstuffs of low digestibility was there a benefit in formulating diets on a digestible amino acid basis. The results of these experiments with laying hens suggest that their amino acid requirements are over-generous. Although 85% of requirements gave generally depressed performance (Table 10), this was not observed when included at 90% of requirements (Table 12). There was also no clear indication that formulating diets to a digestible amino acid requirement gave improved performance over that when formulated on a total basis. Feed conversion ratio which might show some response to a marginal amino acid insufficiency was not different between diets in experiment 2. It did show a clear decline on diets with 85% of requirements in experiment 1. It is interesting that although broilers showed no significant difference in growth rate that related to total or digestible amino acid levels on any of the diets, there was an indication that growth rate tended to be inferior on the digestible amino acid formulations. Compared to the total, FCR also tended to be worse on these latter diets. The reason for this may be that the digestible amino acid requirements of broilers are not known precisely. It is however clear that diets formulated to 100% of digestible amino acid specifications are over-specified by at least 10%. Alternatively, the method used to determine the true digestibility of amino acids, using caectomized cockerels force-fed individual ingredients, may not be appropriate. However the response by starter broiler chickens to diets with a range of total and digestible threonine values would not confirm this. Food intake was increased on all diets formulated on a total compared to a digestible amino acid basis; consequently FCR was poorer on the former compared to the latter diets. The values found for the total and digestible threonine requirements of broilers during the starter phase (3-24 days) are higher than those found in the 16

24 literature particularly when FCR is used as the criterion of response. This indicated that the rapid growth of the modern broiler chick requires an increased level of threonine to support this rapid growth. 17

25 Implications The use of digestible amino acids in diet formulation does not appear to be justified unless ingredients are being used that are known either to vary greatly or to have low digestible amino acid coefficients, e.g. cottonseed meal, some meat and bone meals. Considerable saving can be made for both layers and broilers in fine-tuning specifications for some essential amino acids. From these studies, requirements for egg production may be over 10% too high, while those for broilers may be from 5-10% too high. Although it is recognised that feed formulators must err on the generous side in determining amino acid specifications there is opportunity to optimise diets in order to give maximum economic returns. The requirements for both total and digestible threonine are currently higher than those now in use in broiler starter diets, particularly when FCR is used as the criterion for response. However, the benefits of increasing dietary threonine from the previous published requirements to those found here is about g/kg, and this may not be economically viable. Recommendations It would be prudent if feed formulators were tore-examine their nutrient specifications for both layers and broilers with a view to reducing some and giving reductions in diet costs. The advantage of digestible versus total amino acids in diet formulation is problematic unless unusual ingredients are being used. The method of determining digestible amino acids in feedingstuffs should also be considered carefully. Furthermore, the use of adult birds to undertake these measurements and to extrapolate the results to growing broilers may not always be appropriate. 18

26 References Anonymous (1989). Nutrition Guide. Feed Formulation with Digestible Amino Acids 1 st edition 35 pp. Rhone Poulenc Animal Nutrition, Commentry. AOAC (1984). Association of Official Analytical Chemists (1984). Methods of Analysis, 14 th edition. Association of Official Analytical Chemists, Washington, DC. Fernandez, S.R., Zhang, Y., and Parsons, C.M. (1995). Dietary formulation with cottonseed meal on a total amino acid versus a digestible amino acid basis. Poultry Science 74, Green, S and Kiener, T. (1989). Digestibilities of nitrogen and amino acids in soybean, sunflower, meat and rapeseed meals measured with pigs and poultry. Animal Production 48, Johnson, R.J. (1992). Principles. problems and application of amino acid digestibility in poultry. World's Poultry Science Journal 48, Low, A.G. (1977). Digestibility at several sites in pigs. Proceedings of the Nutrition Society 36, McNab, J.M. (1995). Amino acid digestibilities : determination and application. In Recent Advances in Animal Nutrition in Australia, pp Eds J.B. Rowe and J.V. Nolan. The University of New England, Armidale. Perez-Maldonado, R.A. Mannion, P.F. and Farrell, D.J. (1998). Practical levels of inclusions of four grain legumes in broiler diets in a large-scale experiment. Proceedings Australian Poultry Science Symposium 10, Ravindran, V., Hew, L.I. and Bryden, W.L. (1998). Digestible Amino Acids in Poultry Feedstuffs. RIRDC Publication No. 98/9, Project No. US-67CM PRF Occasional Bulletin No. 4. Rostagno, H.S., Pupa, J.M.R. and Pack, M. (1995). Diet formulation for broilers based on total versus digestible amino acids. Journal of Applied Poultry Research 4, SCA (1987). Standing Committee on Agriculture Poultry Sub Committee. Feeding Standards for Australian Livestock Poultry 76 pp. Sibbald, I.R. (1987). Estimation of bioavailable amino acids in feedingstuffs for poultry and pigs : a review with emphasis on balanced experiments. Canadian Journal of Animal Science 67: Steel, R.G.D. and Torrie, J.H. (1960). Principles and Procedures of Statistics. McGraw Hill, New York. Terpstra, K. (1997). Determination of digestibilities of protein and amino acids in poultry feeds. Proceedings V th International Symposium of Amino Acids, pp Budapest, February Yaharjo, Y.C. and Farrell, D.J. (1984). Effects of caecectomy and dietary antibiotics on the digestibility of amino acids in poultry feeds determined by excreta analysis. Australian Journal of Experimental Agriculture and Animal Husbandry 24,

27 ATTACHMENT 2 COMPENDIUM SUMMARY Project Title Objectives Background Research A COMPARISON OF TOTAL AND DIGESTIBLE AMINO ACIDS IN DIETS FOR BROILERS AND LAYERS 1. To measure the chemical composition of two feed grains and nine protein concentrates and determine the digestibility of their amino acids using caecetomized adult cockerels and excreta collection, following forcefeeding. 2. To compare production of hens and growth rate of broiler chickens on diets formulated on a total and digestible amino acid basis and to identify any economic benefits. 3. To determine the total and digestible amino acid requirement of starter broilers to 24 days of age. There is considerable debate as to the merits of formulating poultry diets on a total or digestible amino acid basis. There is also debate regarding the method used to measure in vivo the amino acid digestibility of feed ingredients as there are several options. It is known that some feedstuffs give a low digestibility coefficient for some essential amino acids e.g. cottonseed meal, heat-damaged proteins. Most feed ingredients have comparatively high amino acid digestibility values (>80%), thus when formulating diets on a total amino acid basis this difference of <20% is normally taken into account by the nutritionist. There have been few experiments that have been designed to test the hypothesis that formulating diets on the basis of digestible rather than on a total amino acid basis gives an economic advantage when using conventional feedingstuffs. This was the basis of experiments designed here. Threonine is an important essential amino acid and is usually third limiting in poultry diets. With changes in genotypes that grow faster and with improved food efficiency there is the need to re-evaluate broiler requirements for threonine. This was done with broilers grown to 24 days of age Small quantities of eleven feed ingredients were transported to France to be assayed for chemical composition and total digestible amino acids using standard procedures. A modified Sibbald method was used with caecetomized adult cockerels. The fore-fed birds gave a true digestible amino acid profile for each ingredient. Apparent metabolisable energy of diets was determined using laying hens and total 20

28 Outcomes Implications collection over four days (classical method). There were two practical type layer experiments in which diets were formulated to 100% and 85% of total and digestible amino acid basis (experiment 1) or to 97% and 90% basis (experiment 2). In a large-scale broiler trial diets were also formulated to a total or digestible amino acid basis ranging from 100% to 91% of requirements in increments of 3%. In determining total and digestible threonine requirements, a summit diet and a basal diet were blended to give levels that ranged from well below to well-above requirements. These were offered separately to male or female broiler chicks from 3-24 days of age. Analyses of the feed ingredients agreed with those reported in the literature. With few exceptions amino acid digestibility coefficients were high however cottonseed meal and one meat and bone meal (B) gave generally lower values than the other ingredients. The first layer experiment gave no differences in any production parameter between diets formulated on a total or digestible amino acid basis at 100% of requirements. The broiler growth trial showed no differences in growth rate and FCR at 42 days between diets. Since there was no sex x diet interaction, groups were combined for each diet. FCR at 21 days showed some differences between diets. In all cases there was a tendency for diets formulated on total rather than digestible amino acid basis to give better performance. Total and digestible threonine requirements were higher than those previously reported. The actual value varied depending on whether growth rate or FCR was used as the parameter of responses. The results of the experiments in which digestible and total amino acid formulations were used suggest that nutrient specifications for layer and broiler diets may be too high. With conventional ingredients, there does not appear to be any clear advantage in using digestible rather than total amino acid values. If anything total gave a non significant advantage over digestible in the broiler experiment. Although the diet formulated to 90% of digestible amino acid specifications gave the lowest cost ($/kg eggs) in experiment 2. Caution must be exercised when interpreting some of these results because of the method of determining amino acid digestibility. The use of excreta for amino acid analysis even in caecetomized adult birds raises some doubts. Finally the recent genotypes of broiler that grow more rapidly with lower FCR's than previously would be 21

29 expected to have increased amino acid requirements. This was shown to be true for threonine but this increase should be evaluated on an economic basis by the feed formulators. Publications Mannion, P.F., Perez-Maldonado, R., and Farrell, D.J. (1998). Responses of meat chickens to diets differing in total and digestible threonine content. Proc. Aust. Poult. Sci. Symp. 1998, 8, Project Details Project Number Project Supervisors Organisation: UQ-52 AJ D.J. Farrell P.F. Mannion The Queensland Poultry Research and Development Centre through The Queensland Department of Primary Industries Phone No. (07) Facsimile No. (07)