A comparison of total and digestible amino acids
in diets for broilers and layers
D.J. Farrell
a,b,*, P.F. Mannion
a, R.A. Perez-Maldonado
a aThe Queensland Poultry Research and Development Centre, PO Box 327,Cleveland, Qld. 4163, Australia
bSchool of Land and Food, The University of Queensland, St. Lucia, Qld 4072, Australia
Received 14 October 1998; received in revised form 17 March 1999; accepted 9 June 1999
Abstract
Eleven samples of food ingredients were analysed for their total and true digestible amino acid content, apparent metabolisable energy and other components. Large batches of these ingredients were retained for a broiler and a layer experiment. Four layer diets were formulated at 0.97 and 0.90 of total and digestible amino acid requirements for egg production using the analysed ingredients. Eight broiler diets were also formulated from 1.0 to 0.91 of total and digestible amino acid requirements in starter and finisher diets. Proximate and amino acid analyses and AME values were within the normal range for the 11 foodstuffs. Digestibility of amino acids was high with very few exceptions, e.g. cottonseed meal, meat and bone meal. Diets formulated on a total or digestible amino acid basis gave no differences in egg production parameters or broiler production parameters with no effect of level of inclusion. However, the main effects showed that diets formulated on a total compared to a digestible amino acid basis gave better growth rate and feed conversion efficiency in broilers. It was concluded that nutrient specifications for layers and broilers are not sufficiently precise to be able to differentiate between 1.97 and 0.90 of requirement for egg production or 1.0 and 0.91 for broiler growth. The use of digestible amino acids may be justified in diet formulations only when unusual protein concentrates with low amino acid digestibility values are used in large amounts.#1999 Elsevier Science B.V. All rights reserved.
Keywords: Ingredient amino acid digestibility; AME values 82 (1999) 131±142
*Corresponding author. Tel.:61-7-3824-3081; fax.:61-7-3824-4316
E-mail address: farreld@dpi.qld.gov.au (D.J. Farrell)
1. Introduction
It is well known that not all of the amino acids in a feedingstuff are digested by the bird and become 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 coefficients of individual amino acids within a feedstuff may differ considerably.
The methods used to measure amino acid digestibility vary greatly and these have been reviewed on numerous occasions (Sibbald, 1987; Johnson, 1992; McNab, 1995; Raharjo and Farrell, 1984a). Site of sampling material for analysis is important and the indigestible marker used to calculate amino acid digestibility may also differ 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 (Raharjo and Farrell, 1984b). However, there are few tables that provide information on the digestibility of 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 have 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), or over-processed meals (Fernandez and Parsons, 1996) to demonstrate an advantage. There are very few published papers that have demonstrated a significant improvement in practical diets for layers and for broilers formulated on the basis of digestible amino acids when several conventional dietary ingredients have been combined.
The purpose of the two 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 practical layer and broiler diets using a range of foodstuffs.
2. Materials and methods
2.1. Bioassays and chemical analyses
Substantial quantities of 11 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 amino acid bioassay using adult birds (Sibbald, 1987) with modifications (Anonymous, 1989) to determine true amino acid digestibility. Isabrown 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 at each level of inclusion per dietary treatment and six hens on the all-grain diets. The two
grains were included at 980 g/kg 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 20 g/kg of the diet. AME was calculated by regression analysis and then extrapolating the line to the rate of inclusion of the test ingredient of 1000 g/kg diet. Chemical analyses of the raw ingredients followed the methods of the AOAC, 1984. Gross energy was determined in an adiabatic bomb calorimeter.
2.2. Layer experiment
A least-cost formulation package (Feedmania) was used to construct diets using the determined amino acid and AME values for the feedstuffs.
In the layer experiment, diets were formulated to 97% and 90% of total and of digestible amino acid requirements (SCA, 1987; Anonymous, 1989). The composition of the least-cost formulated diets is given in Table 1. Each diet was fed for 20 weeks to 50 individually-caged Isabrown birds housed in a saw-tooth shed with open sides and adjustable side curtains.
Table 1
Ingredient and calculated chemical composition (g/kg as fed basis) of diets formulated on a total (T) and digestible (D) amino acid basis at 0.97 and 0.90 of amino acid recommendations (Layer experiment)
T-97 T-90 D-97 D-90
Sorghum 280 303 269 291
Wheat 280 303 269 291
Cottonseed meal 70 70 70 70
Faba beans 94 67 97 72
Meat and bone meal B 67 50 67 67
Rapeseed meal 87 81 85 89
Soybean meal ± ± 22 ±
Soybean oil 38.5 36.7 38 37
Limestone 79 82 79 79
Dical P ± 1.3 ± ±
Sodium chloride 1.9 2.1 1.9 1.8
DL-methionine 0.6 0.6 0.7 0.5
Vitamin premixa 2.3 2.3 2.3 2.3
Chemical composition
Crude protein 177 164 158 150
AME (MJ/kg) 11.9 11.9 11.9 11.9
Lysine 7.3 6.4 6.3 5.6
Methionine 3.2 3.0 2.9 2.7
Methoninecyst 6.1 5.7 5.1 4.8
Tryptophan 2.1 2.1 1.9 1.8
Threonine 5.7 5.2 4.8 4.5
aThe vitamin and mineral premix added per kg of diet: 2.5 mg retionol, 75
mg cholecalciferol, 5 mg a-tocopherol acetate, 2 mg menadione sodium bisulfite, 1 mg thiamine, 4 mg riboflavin, 2 mg pyridoxine, 10mg cyanocobalamin, 1 mg folic acid, 10 mg niacin, 10 mg Ca pantothenate, 30mg biotin, 150 mg choline, 50 mg Mn, 50 mg Zn, 50 mg Fe, 600mg Mo, 500mg Co, 600mg I, 4 mg Cu, 70mg Se, 80 mg Banox (BHABHT).
Diets were fed ad libitum in mash form. A mineral and vitamin layer premix and a yolk pigmentor were added to all diets at the recommended levels. Egg production was recorded on five days each week, eggs were weighed weekly, food intake recorded monthly and egg specific gravity measured monthly. Hens were weighed at the start and end of the experiment.
2.3. Broiler experiment
Diets were formulated to total and digestible amino acids at 1.0, 0.97, 0.94 and 0.91 of nutrient requirements for starter and finisher broilers (SCA, 1987), taking into account the total and digestible amino acid requirements reported by Baker et al. (1993) and Han and Baker (1994), and the ideal ratios of amino acids (Baker and Han, 1994; Baker et al., 1993) for starter and finisher broilers. The starter diets were fed to 21 days and the finisher diets from 22 to 41 days of age. The diets are shown in Tables 2 and 3.
Table 2
Broiler diets formulated to total (T) and digestible (D) amino acid requirements that range from 1.0 to 0.91 of requirement
Starter formulations (g/kg)
T-100 T-97 T-94 T-91 D-100 D-97 D-94 D-91
Ingredients
Wheat 270 280 290 300 280 290 290 300
Sorghum 272 281 289 298 274 282 299 307
Cottonseed meal 50 50 50 50 50 50 50 50
Fish meal 30 30 30 30 30 30 30 30
Meat and bone meal A 35 39 30 39 30 30 30 30
Meat and bone meal B 33 30 38 30 37 37 38 38
Sweet lupins 40 40 40 40 40 40 40 40
Soybean meal 216 198 181 162 205 188 172 155
Sunflower oil 35 34 33 32 35 33 32 31
Limestone 7.3 7.3 7.2 7.3 7.2 7.2 7.2 7.3
Sodium chloride 1.4 1.4 1.4 1.4 1.4 1.4 1.4 1.4
Vitmin premixa 6.7 6.7 6.7 6.7 6.7 6.7 6.7 6.7
DL-methionine 1.9 1.8 1.7 1.6 1.8 1.7 1.6 1.5
L-lysine HCl 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5
Chemical composition (g/kg)
Crude protein 244 239 234 228 214 209 205 200
AME (MJ/kg) 12.7 12.7 12.7 12.7 12.7 12.7 12.7 12.7
Lysine 12.7 12.3 11.9 11.6 10.8 10.5 10.2 9.8
Methionine 5.6 5.4 5.2 5.0 5.0 4.8 4.6 4.5
Methcyst 9.3 9.0 8.7 8.5 7.8 7.5 7.3 7.1
Tryptophan 3.0 2.9 2.8 2.7 2.5 2.4 2.4 2.3
Threonine 8.3 8.1 7.9 7.7 7.2 7.0 6.8 6.6
aThe vitamin and mineral premix added per kg of diet: 3.75 mg retinol, 112
mg D3, 30 mg a-tocopherol
acetate, 3 mg menadione sodium bisulfite, 1.5 mg thiamine, 6 mg riboflavin, 3 mg pyridoxine, 15mg B12,
1.5 mg folic acid, 55 mg niacin, 15 mg Ca pantothanate, 180mg biotin, 600 mg choline, 75 mg Mn, 75 mg Zn, 75 mg Fe, 900mg Mo, 750mg Co, 900mg I, 6 mg Cu, 105mg Se, 120 mg Banox.
Chicks of a commercial strain (Cobb) 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 in floor pens with wood shavings as litter. Treatments were assigned randomly in blocks of eight pens. Birds and food were weighed at 1, 21 and 41 days of age. Lighting was adjusted according to commercial practice (Farrell et al., 1999). Mortality was recorded daily.
Data were analysed using a randomised block analysis of variance model (SAS/STAT 6.04, 1987: SAS Institute Inc., Cary, North Carolina). For broiler treatments therefore all factorial combinations of two types of amino acids and four levels of formulation; for layer treatments, there were two types of amino acids and two levels of formulation. Main effect means and interaction means were compared using the protected LSD test operating at the 0.05 level of significance. Regression analysis was also undertaken (Steel and Torrie, 1960).
The experiments were approved by the Animal Research Institute's Animal Ethics Review Committee.
Table 3
Broiler diets formulated to total (T) and digestible (D) amino acid requirements that range from 1.0 to 0.91 of requirements
Ingredients Finisher formulations (g/kg)
T-100 T-97 T-94 T-91 D-100 D-97 D-94 D-91
Wheat 300 300 300 300 300 300 300 300
Sorghum 327 338 349 361 308 326 345 363
Cottonseed meal 65 68 72 75 ± ± ± ±
Fish meal 30 30 30 30 30 30 30 30
Meat and bone meal (B) 54 53 51 50 54 54 54 54
Soybean meal 160 147 133 120 180 163 147 130
Sunflower meal ± ± ± ± 66 65 65 64
Sunflower oil 40 40 40 40 41 39 38 36
Limestone 8.3 8.0 9.0 8.8 7.7 7.7 7.8 7.8
Dicalcium phosphate 2.3 2.6 2.9 3.2 2.3 2.4 2.5 2.5
Sodium chloride 1.7 2.0 2.0 1.7 1.7 1.7 1.7 1.7
VitMin premixa 6.7 6.7 6.7 6.7 6.7 6.7 6.7 6.7
DL-methionine 2.2 2.0 2.0 1.7 1.9 1.8 1.8 1.7
L-lysine HCl 1.7 1.6 1.67 1.5 1.0 1.1 1.2 1.3
Chemical composition (g/kg)
AME (MJ/kg) 13 13 13 13 13 13 13 13
crude protein 221 217 212 208 199 194 189 184
Lysine 11.1 10.8 10.4 10.1 9.4 9.1 8.9 8.6
Methionine 5.5 5.0 5.0 4.9 5.0 4.9 4.7 4.6
Methcyst 8.8 9.0 8.0 8.0 7.7 7.5 7.2 7.0
Tryptophan 2.6 3.0 2.0 2.4 2.3 2.2 2.2 2.1
Threonine 8.2 8.0 8.0 7.4 7.0 6.8 6.6 6.4
aThe vitamin and mineral premix added per kg of diet: 3.75 mg retinol, 112
mg D3, 30 mg a-tocopherol
acetate, 3 mg menadione sodium bisulfite, 1.5 mg thiamine, 6 mg riboflavin, 3 mg pyridoxine, 15mg B12,
1.5 mg folic acid, 55 mg niacin, 15 mg Ca pantothanate, 180mg biotin, 600 mg choline, 75 mg Mn, 75 mg Zn, 75 mg Fe, 900mg Mo, 750mg Co, 900mg I, 6 mg Cu, 105mg Se, 120 mg Banox.
3. Results
The proximate analysis of the 11 ingredients used is given in Table 4, and their amino acid profiles in Table 5. The two meat and bone meals contained 535 g crude protein (A), and 596 g crude protein (B)/kg on an 'as is' basis. The true digestibility of the amino acids for each ingredient is given in Table 6.
The two meat meals showed considerable differences in amino acid digestibility coefficients. Digestible lysine and threonine coefficients were 0.83 and 0.86; and .75 and 0.78 for meat meals A and B, respectively. Cottonseed meal had the lowest lysine digestibility of 0.60, followed by meat meal B of 0.78.
The apparent metabolisable energy of nine of the 11 ingredients is given in Table 7. 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).
3.1. Layer experiment
The overall results of the layer experiment showed no significant treatment effect on any parameter (Table 8). There was some indication that the diet formulated to 0.90 of total amino acid requirements gave a lower egg mass by 2 g/day compared to other treatments.
3.2. Broiler experiment
The results are shown in Table 9. Since there was no dietsex interaction, data were combined for the two sexes. Growth rate and FCR to 41 days were about the same as industry standards. The only difference between dietary treatments was in FCR during the starter phase. Mean liveweight gain at 21 days of age was significantly higher (p< 0.05)
Table 4
Proximate analysis of feed ingredients on an `as fed' basis (g/kg)
Crude
Cotton seed meal 392 895 63 17 121
Soybean meala 423 890 57 27 87
Sorghum 108 856 16 33 26
Lupins 255 904 30 57 157
Faba beans 237 879 33 15 91
Sunflower meal 337 915 57 16 210
Rapeseed 285 917 35 306 82
Wheat 162 898 16 14 28
Meat and bone meal Ab 535 950 233 147 nd
Meat and bone meal Bc 596 950 263 87 nd
Fish meald 657 915 152 66 nd
aUrease activity: 0.11 mg N (from ammonia)/(g*min). bCa73.3, Phos36.8.
cCa
86.6, Phos42.1.
dCa33.7, Phos22.4.
on the diets formulated to total (723 g) compared to digestible (709 g) amino acid specifications. This same trend (p< 0.01) was seen at 41 days (2189 g vs. 2152 g) of age. FCR was also worse (p0.05) when data were combined for digestible (1.43) compared to total (1.40) amino acids at 21 days. A similar trend (p0.06) was observed for FCR at 41 days of age. When data at 21 days were combined, there was a significant (p< 0.05) decline in FCR as formulations increased from 0.91 to 1.0 of amino acid specifications.
4. 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 ingredients had not deteriorated visibly during this time. However, the two grains were later replaced with grains of similar protein content for the broiler trial because of deterioration.
Table 5
Amino acid content of feed ingredients on an `as fed' basis (g/kg)
CSMa SBMb Sorgc Lupd Fabe SFf Rapg Whh MBAi MBBj FMk Leu 21.2 31.3 14.1 15.9 16.9 21.2 19.4 10.3 32.2 33.1 46.6 Tyr 10.5 15.6 4.2 9.5 8.1 9.6 8.3 5.2 13.0 13.1 21.5
Table 6
True digestibility coefficients of protein and amino acids in 11 feed ingredients measured using adult caecetomised cockerels
CSMa SBMb Sorgc Lupd Fabe SFf Rapg Whh MBAi MBBj FMk
Protein 0.791 0.887 0.913 0.934 0.835 0.904 0.881 0.918 0.857 0.824 0.918 Asp 0.785 0.865 0.919 0.917 0.875 0.884 0.873 0.844 0.662 0.589 0.856 Thr 0.729 0.842 0.906 0.918 0.842 0.885 0.845 0.877 0.833 0.750 0.914 Ser 0.764 0.868 0.933 0.918 0.853 0.866 0.859 0.919 0.801 0.732 0.897 Glu 0.873 0.901 0.958 0.955 0.934 0.950 0.927 0.968 0.834 0.761 0.911 Pro 0.791 0.872 0.934 0.919 0.851 0.903 0.863 0.966 0.790 0.778 0.862 Gly 0.718 0.802 0.905 0.904 0.804 0.784 0.845 0.869 0.787 0.769 0.839 Ala 0.710 0.826 0.955 0.863 0.862 0.863 0.878 0.852 0.782 0.745 0.849 Val 0.766 0.852 0.923 0.905 0.857 0.907 0.860 0.904 0.833 0.696 0.876 Ile 0.737 0.874 0.939 0.927 0.871 0.919 0.878 0.922 0.855 0.785 0.914 Leu 0.760 0.867 0.959 0.936 0.892 0.917 0.897 0.930 0.862 0.702 0.925 Tyr 0.834 0.902 0.952 0.961 0.865 0.932 0.886 0.941 0.877 0.796 0.921 Phe 0.846 0.882 0.950 0.934 0.886 0.932 0.901 0.938 0.856 0.826 0.905 Lys 0.601 0.888 0.860 0.884 0.888 0.873 0.870 0.828 0.856 0.778 0.913 His 0.822 0.891 0.912 0.930 0.865 0.908 0.920 0.914 0.849 0.793 0.908 Arg 0.892 0.930 0.937 0.927 0.921 0.956 0.932 0.896 0.861 0.820 0.921 Cys 0.731 0.807 0.864 0.855 0.669 0.772 0.763 0.896 0.612 0.370 0.743 Met 0.776 0.902 0.917 0.877 0.797 0.942 0.925 0.921 0.888 0.823 0.923 Try 0.796 0.875 0.927 0.914 0.806 0.884 0.887 0.902 0.822 0.688 0.897
aCottonseed meal.
The apparent metabolisable energy (MJ/kg DM) of nine ingredients
Cottonseed meal 7.21
Fish meal 12.11
Meat and bone meal A 11.01
Meat and bone meal B 12.28
Rapeseed (full fat) 14.27
Sunflower meal 7.18
Soybean meal 11.35
Sorghum 14.67
Wheat 12.91
The chemical composition and AME values were typical of each ingredient and agreed well with published data. Amino acid content and their true digestibility coefficients were also generally high and similar to those reported for these ingredients. The two exceptions were meat and bone meal B and cottonseed meal where true lysine digestibility was 0.78 and 0.60, respectively. Surprisingly, meat and bone meal B had a high crude protein content of 600 g/kg (Table 4). Composition of the starting material and heat treatment can affect amino acid digestibility of meat and bone meals. Except for wheat, cottonseed meal and meat and bone meal B, digestibility coefficients for lysine varied from 0.86 to 0.91, and for threonine from 0.84 to 0.92 for the remaining ingredients. 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 the amino acid requirements used are normally over-Table 8
Performance of birds on diets formulated to 0.97 and 0.90 of amino acid requirements on a total and digestible basis over 20 weeks
Total Digestible SEM Pa
0.97 0.90 0.97 0.90
Egg production (%) 90.9 87.3 89.8 89.0 1.81 0.28
Food intake (g/day) 106.8 105.9 108.5 107.6 1.80 0.99
Egg weight (g) 61.4 61.3 61.7 61.5 0.69 0.91
Egg mass (g/day) 55.8 53.5 55.4 55.8 1.23 0.33
Food conversion ratio (g/g) 1.92 2.00 1.98 1.99 0.043 0.24 Specific gravity 1.087 1.088 1.088 1.087 0.0009 0.24 Body weight change (kg) 0.204 0.187 0.186 0.152 0.0346 0.504
aProbability.
Table 9
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 0.91ÿ1.0 of requirements
Diet Amino acid
(21 days) (21 days) (41 days) (41 days)
1 T 1.0 726 1.39bc 2192 1.78
2 T 0.97 728 1.39c 2192 1.79
3 T 0.94 726 1.41abc 2205 1.81
4 T 0.91 714 1.43a 2167 1.81
5 D 1.0 717 1.41abc 2163 1.80
6 D 0.97 706 1.43ab 2165 1.81
7 D 0.94 711 1.42abc 2142 1.81
8 D 0.91 701 1.45a 2134 1.87
Probability 0.44 0.045 0.15 0.18
SEM 14.3 0.018 27.4 0.015
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 the indigestibility of the amino acids in the experimental diets. Thus, it is not surprising that we were unable to demonstrate a significant difference in performance when formulating on a total vs. digestible amino acid basis particularly as ingredients of very low digestibility were not used in significant amounts. As pointed out in SCA (1987), estimates of amino acid allowances for poultry have already taken their digestibility into account.
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.
Wang and Parsons (1998) were unable to show a consistent advantage in using digestible amino acids in diets containing high and low quality meat and bone meals when fed to broilers. They conceded that the method of measurement used to determine true amino acid digestibility may overestimate amino acid bioavailability.
The results of the experiment with laying hens suggest that their amino acid requirements are over-generous. Excellent production was observed when amino acids were included at only 0.90 of requirements. 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.
Recently, Schutte and Swink (1998) found that the total lysine requirement of a laying hen consuming 110 g/day of a diet with a calculated AME content of 11.8 MJ/kg was 7.3 g/kg for maximum egg mass but higher for optimum food efficiency. For apparent faecal digestible lysine the figure was 5.37 g/kg. These are similar to those values used here (Table 1) for diets with 0.97 of requirements and higher than our 0.90 formulation. The faecal digestibility method for measuring amino acids will likely give raised values for the reasons discussed previously.
It is interesting that although broilers showed no significant difference in growth rate that related to total or digestible amino acids 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 1.0 of digestible amino acid specifications are over-specified by at least 10%.
Han and Baker (1994) found that optimum food efficiency was seen for digestible lysine at 8.9 g/kg for males and 8.5 g/kg for females between three and six weeks of age. These values are slightly lower than the 9.4 g/kg used in the 1.0 digestible lysine formulation (Table 3) for both sexes.
The requirement for total lysine (Table 2) was only marginally higher than that recommended by NRC (1994) for starter birds (12.2 g/kg) but is in line with that predicted by a computer simulation model (Gous, 1998). It is the same as that recommended by the NRC (1994) for birds 3±6 weeks of age.
Alternatively, the method used to determine the true digestibility of amino acids, using caecectomised cockerels force-fed individual ingredients, may not be appropriate.
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 in amino acid composition or to have low digestible amino acid coefficients, e.g. cottonseed meal, canola meal, some meat and bone meals.
In conclusion, considerable savings 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% to 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.
5. Acknowledgements
We thank the RIRDC (Chicken Meat and Egg Programs) for financial support and the staff at QPRDC for skilled technical assistance.
References
Anonymous, 1989. Nutrition Guide. Feed Formulation with Digestible Amino Acids 1st ed., pp. 35. Rhone Poulenc Animal Nutrition, Commentry.
Association of Official Analytical Chemists, 1984. Official Methods of Analysis, 14th ed. Association of Official Analytical Chemists, Washington, DC.
Baker, D.H., Han, Y., 1994. Ideal amino acid profile for chickens during the first three weeks of growth. Poult. Sci. 73, 1441±1447.
Baker, D.H., Parsons, C.N. Fernandez, S.A., Aoygai, S., Han. Y., 1993. Digestible amino acid requirements of broiler chickens based upon ideal protein considerations. Proc. Arkansas Nut. Conf. University of Arkansas, Fayetteville, A.R., pp. 22-24.
Farrell, D.J., Perez-Maldonado, R.A., Mannion, P.F., 1999. The optimum inclusion of field peas, faba beans, chick peas and sweet lupins in poultry diets. II Broiler experiments. Br. Poult. Sci. (in press).
Fernandez, S.R., Parsons, C.M., 1996. Bioavailability of digestible lysine in heat-damaged soybean meal for chick growth. Poult. Sci. 75, 224±231.
Fernandez, S.R., Zhang, Y., Parsons, C.M., 1995. Dietary formulation with cottonseed meal on a total amino acid versus a digestible amino acid basis. Poult. Sci. 74, 1168±1179.
Gous, R.M., 1998. Making progress in the nutrition of broilers. Poult. Sci. 77, 111±117.
Green, S., Kiener, T., 1989. Digestibilities of nitrogen and amino acids in soybean, sunflower, meat and rapeseed meals measured with pigs and poultry. Anim. Prod. 48, 157±179.
Han, J., Baker, D.H., 1994. Digestible lysine requirements of male and female broiler chicks during the period three to six weeks posthatching. Poult. Sci. 13, 1739±1745.
Johnson, R.J., 1992. Principles. problems and application of amino acid digestibility in poultry. Wld's Poult. Sci. J. 48, 232±246.
Low, A.G., 1977. Digestibility at several sites in pigs. Proc. Nut. Soc. 36, 189±194.
McNab, J.M., 1995. Amino acid digestibilities : determination and application. In: Rowe, J.B., Nolan, J.V. (Eds.), Recent Advances in Animal Nutrition in Australia. University of New England, Armidale, NSW, pp. 7±13.
Perez-Maldonado, R.A., Mannion, P.F., Farrell, D.J., 1998. Practical levels of inclusions of four grain legumes in broiler diets in a large-scale experiment. . Proc. Aust. Poult. Sci. Symp. 10, 144±147.
Raharjo, Y., Farrell, D.J., 1984a. A new biological method for determining amino acid digestibility in poultry feedstuffs using a simple cannula and the influence of dietary fibre on endogenous amino acid output. Anim. Feed Sci. Technol. 12, 29±45.
Raharjo, Y.C., Farrell, D.J., 1984b. Effects of caecectomy and dietary antibiotics on the digestibility of amino acids in poultry feeds determined by excreta analysis. Aust. J. of Exp. Agric. and Anim. Husb. 24, 516±521. Ravindran, V., Hew, L.I., Bryden, W.L., 1998. Digestible Amino Acids in Poultry Feedstuffs. RIRDC
Publication No. 98/9, Project No. US-67CM PRF Occasional Bulletin No. 4.
Rostango, H.S., Pupa, J.M.R., Pack, M., 1995. Diet formulation for broilers based on total versus digestible amino acids. J. of Appl. Poult. Res. 4, 293±299.
SCA, 1987. Standing Committee on Agriculture Poultry Sub Committee. Feeding Standards for Australian Livestock Poultry CSIRO, East Melbourne, Vic.
Schutte, J.B., Swink, W., 1998. Requirement of the laying hen for apparent fecal digestible lysine. Poult. Sci. 77, 697±701.
Sibbald, I.R., 1987. Estimation of bioavailable amino acids in feedingstuffs for poultry and pigs : a review with emphasis on balanced experiments. Can. J. of Anim. Sci. 67, 221±301.
Steel, R.G.D., 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. Proc. Vth Int. Symp. on Amino Acids, Budapest, February 1997 pp. 221±226.
Wang, X., Parsons, C.M., 1998. Dietary formulation with meat and bone meal on a total versus a digestible amino acid basis. Poult. Sci. 77, 1010±1019.
