Applicability of the True Metabolizable Energy System in Practical Feed Formulation

Applicability of the True Metabolizable Energy System in Practical Feed Formulation N. M. DALE and H. L. FULLER

Department of Poultry Science, University of Georgia, Athens, Georgia 30602 (Received for publication March 12, 1981)

INTRODUCTION

MATERIALS AND METHODS

In the true metabolizable energy (TME) system of Sibbald (1976), the caloric content of feedstuffs is assayed using roosters as the experimental subject. The roosters are first fasted and are then either force-fed a precisely measured quantity of the material being assayed or held without food so as to estimate endogenous energy loss. As the experimental conditions imposed during the TME assay have little resemblance to those employed in the practical rearing of poultry, it cannot be assumed that TME values would necessarily be an applicable measure of the available energetic content of feedstuffs. Sibbald (1977a) and Dale and Fuller (1980) found the TME values of individual feed ingredients to be additive, suggesting the feasibility of using the values in practical feed formulation. A more meaningful test of the applicability of TME would be one based on actual chick performance. It is die purpose of this set of experiments to evaluate the TME system on the basis of its ability to correlate with observed production parameters of broiler chicks.

In the first study, the TME and the apparent metabolizable energy (AME) contents of five diets of increasing caloric and nutrient density and chick response to these diets were compared. In the second study, the TME of a number of feed ingredients was determined, and chick response to diets formulated on the basis of these determinations was assumed to be an indicator of the relative applicability of TME values. Experiment 1. Five test diets were formulated which, on a calculated basis, increased progressively in energy and nutrient density while maintaining the same calorie:protein ratio (Table 1). Three groups of 10 male broiler chicks (Hubbard) housed in battery brooders received each of the five diets ad libitum from 0 to 3 weeks of age. Feed consumption and body weight gains were recorded. During the final four days of the experiment, the AME content of each diet was assayed using the total collection technique. All diets were simultaneously assayed for TME content according to the method of Sibbald (1976) using Single Comb White Leghorn roosters (Shaver). Eight roosters 351

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ABSTRACT Two experiments were conducted to investigate whether values obtained using the true metabolizable energy (TME) assay are applicable in the formulation of practical diets for poultry. In the first study, five diets of increasing energy and nutrient density were assayed for TME and nitrogen corrected, apparent metabolizable energy. (AMEn). Chick response to each diet was evaluated in a 3-week growth trial. The determined TME of three practical diets exceeded the respective determined AMEn by 13 to 14%. A comparison between feed efficiency of chicks and the TME and AMEn content of the test diets indicated that TME values more closely reflected observed chick performance than did AMEn. In the second study, seven feed ingredients were assayed for TME and crude protein content. On the basis of these analyses, four isocaloric, isonitrogenous diets were prepared using the assayed lots of ingredients in varying proportions. In all diets, critical nutrients were included in excess of requirements, energy thus being limiting for optimal chick performance. In a 3-week growth study, chicks receiving each of the test diets exhibited virtually identical body weight gains and feed conversion ratios. Assays of the mixed diets indicated TME values of individual ingredients to be additive to within 1.6% of calculated totals. It was concluded that the TME system provided an accurate measure of metabolizable energy. (Key words: true metabolizable energy, apparent metabolizable energy, applicability, additivity, roosters, broilers) 1982 Poultry Science 61:351-356

DALE AND FULLER

352

TABLE 1. Composition and calculated analysis of diets (Experiment 1) Diets A

B

C

D

E

Yellow corn Soybean meal Corn gluten meal (60% protein) Poultry by-product meal Poultry fat Soy mill feed D-L methionine L-lysine Premix'

55.00 25.30 2.00

55.97 27.78 2.00

55.87 30.15 2.00

52.85 33.00 2.00

47.86 35.60 2.00

4.00 1.50 9.40 .10 .10 2.60 100.00

4.00 2.10 5.30 .09 .07 2.69 100.00

4.00 3.00 2.10 .08 .02 2.78 100.00

4.00 4.70 .50 .08

4.00 7.50

2.87 100.00

2.96 100.00

Calculated analysis AME (kcal/kg) Protein (%) Calorie: protein ratio

2860 21.7 132

2970 22.5 132

3080 23.3 132

3190 24.2 132

.08

3300 25.0 132

'Premix composed of defluorinated phosphate, 54%; limestone, 23%; NaCl, 12.5%; vitamin premix, 7.5%; and trace mineral premix, 3.0%. Trace mineral mix provides (ppm) for diet A; Mn, 60, Zn, 50; Fe, 30; Cu, 5; I, 1.05. Vitamin mix provides per kilogram of Diet A: vitamin A, 11000 IU; vitamin D 3 , 1100 ICU; vitamin E, 11 IU; riboflavin, 4.4 rag; Ca pantothenate, 9.6 mg; nicotinic acid, 44 mg; choline CI, 220 mg; vitamin B 1 2 , 6.6 Mg; vitamin B 6 , 2.2 mg; menadione, 1.1 mg (as menadione sodium bisulfite complex); folic acid, .55 mg; d-biotin, .11 mg; thiamine mononitrate, 2.2 mg; ethoxyquin, 125 mg. Vitamin and trace mineral supplementation increased in diets B, C, D, and E in proportion to energy density.

were force-fed 25 g of t h e respective diet, while a n o t h e r 8 served as fasted controls. Excreta were collected for 4 8 h r postfeeding and were dried for 18 h r in a forced-air oven at 6 0 C. Experiment 2. F o u r feed ingredients (yellow corn, dehulled soybean meal, corn gluten meal, p o u l t r y b y - p r o d u c t meal) were analyzed for p r o x i m a t e composition and TME c o n t e n t , while three others (poultry fat, b e e t molasses,

and glucose m o n o h y d r a t e ) were assayed only for TME and moisture (Table 2). T h e TME assays were c o n d u c t e d as described above, except t h a t p o u l t r y fat replaced 15%, and molasses 25%, of a corn carrier. Excreta collection periods were 30 h r for soybean meal and 4 8 hr for p o u l t r y b y - p r o d u c t meal. On t h e basis of these assays, four isocaloric, isonitrogenous diets were prepared

TABLE 2. Proximate composition and TME content of feed ingredients (Experiment 2)1

Ingredient

Moisture

Crude protein

Crude fiber

Ether extract

TME (kcal/kg)

Yellow corn Soybean meal Poultry by-product meal Corn gluten meal (60% protein) Glucose Poultry fat Molasses (beet) 1

13.9 11.2 4.1

8.3 46.6 64.5

2.2 4.5 1.7

10.1 9.0 <1.0 27.5

61.5

.9

All values expressed on an "air dry" basis.

2.9 2.5 12.4

3 520 2820 3560

.8

4070 3 320 9380 2660

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Ingredient (%)

353

TME APPLICABILITY

In order to test the additivity of TME values determined for the individual feed ingredients, each of the mixed feeds was assayed for TME as described above. RESULTS AND DISCUSSION Experiment 1. Determined AME n and TME contents of the five test diets are shown in Table 4. The TME values were consistently greater than AME n , exceeding the latter by 13 to 14% for diets C, D, and E and by 17 to 18% for the less practical diets A and B. The percent by which the TME of the more practical diets (C, D, and E) exceeded the respective AME n was intermediate between the approximation of 10% of Sibbald (1977b) and 12 to 16% by Halloran(1980). Chicks fed the lower density diets A and B gained less weight than those receiving the higher density diets C, D, and E. Feed efficiency (body weight gain/feed consumption) increased with each increase in dietary density, the increase being significant between diets B and C.

TABLE 3. Composition of test diets (Experiment 2) Diets Ingredients (%)

A

B

C

D

Yellow corn Soybean meal (dehulled) Corn gluten meal (60% protein) Poultry by-product meal Glucose Poultry fat Molasses (beet) Defluorinated phosphate Limestone D-L methionine L-lysine Constant 1

45.00 32.50 5.00

50.00 27.00 6.00

55.00 23.00 7.00

60.00 17.00 9.00

5.00

7.00

8.20

10.00

6.00 2.63 1.00 1.44

4.00 1.83 1.50 1.22

2.00 2.00 1.19 1.06

1.41 .94

.71 .07

.74 .06

.65 100.00

.65 100.00

.76 .04 .10 .65 100.00

.76 .04 .20 .65 100.00

3350 25.0 1.32 .51 1.04 .50

3350 25.0 1.22 .51 1.05 .50

3350 25.0 1.22 .51 1.04 .50

3350 25.0 1.22 .51 1.05 .50

Calculated analysis TME (kcal/kg) 2 Protein (%)2 Lysine (%) Methionine (%) Calcium (%) Phosphorus (available %) 1 2

Provided .25% salt and levels of vitamins and trace minerals listed for diet A, Table 1. Calculated from analysis of individual ingredients.

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using the same lots of ingredients that had previously been assayed but in differing proportions (Table 3). In all cases, crude protein and critical amino acids were provided in excess of requirements at the energy level employed (Thomas e.t al, 1975). For the purpose of estimating these requirements, the nitrogen corrected AME (AME n ) content of the diets was assumed to be 13% less than TME, or roughly 2970 kcal/kg (see results of Experiment 1). Energy was thus the most limiting factor for optimal chick performance; therefore, the applicability of the determined TME values would be reflected by the relative agreement in body weight gains and especially feed conversion ratios among chicks receiving each of the supposedly isocaloric diets. One hundred and sixty male broiler chicks (Hubbard), 1 day of age, were divided into groups of 10 and assigned to pens in battery brooders. Four such groups received each of the four test diets ad libitum from 1 day to 3 weeks of age. Feed consumption and body weight gains were recorded weekly.

DALE AND FULLER

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TABLE 4. Determined caloric content of test diets and performance of chicks (Experiment 1) Diets

AME n (kcal/kg) 1 TME (kcal/kg) 1 TME/AME n Body weight gain g/chick (0-21 days) Gain/feed consumed

A

B

2761 3247 1.18

2861 3351 1.17

412a .56*

C 3066 3459 1.13

417ab

454b .61b

.57*

D

E

3138 3587 1.14

3191 3617 1.13

445ab .62 b

445ab

.65b

1

Air dry basis.

The feed efficiency of chicks receiving the five diets was plotted against the respective determined energetic densities, expressed as AME n and TME (Fig. 1). The observed relationship between determined AME density and feed efficiency paralleled the TME response more closely than did the calculated AME, for which a perfectly linear plot would have been anticipated. The relationship between feed efficiency and kilocalories per kilogram of diet was described by the equation Y = .11 X + .26,

FEED EFFICIENCY

.66 TME

AME

where Y equals feed efficiency and X equals kcal/g expressed as AME n , on a dry basis. The corresponding equation when energy is expressed as TME is Y = .22 X - .16 (Table 5). From comparing die r values of the two equations, it is concluded that the TME values more closely reflect die observed chick response to varying levels of energy density than do the corresponding AME n values. Experiment 2. To test how well the TME content of various feedstuffs reflected the energy available to broilers, the performance was compared of chicks receiving four diets calculated to be isocaloric. In the test diets, critical nutrients were supplied in excess of requirements. It was thus assumed that any actual differences in caloric density would be reflected in variations in chick response. Chicks fed each of the four diets had remarkably similar production characteristics (Table 6). Body weight gains and feed conversions in all treatments were almost identical. It is concluded that the determined TME values gave a precise indication of the metabolizable

.63

.60

.57 TABLE 5. Estimates for the coefficients of regression for the relationship between feed efficiency and system of energy measurement (estimate ± SE)

.54

•f

1

'3000

3400

3800

Slope1

Y Intercept

r2

.11 ± .02 .22 ± .03

.26 ± .08 - . 1 6 ± .12

.56 .80

4200

kcal/kg (dry)

FIG. and feed efficiency of chicks (Experiment 1).

AME n TME 1

Coefficient corresponds to kcal/g of dry diet.

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a ' b Means without common superscript differ significantly (P<.05).

TME APPLICABILITY

355

TABLE 6. Body weight gains and feed conversions (Experiment 2) Diets A Body weight gain + SE (g/chick, 0-21 days) Feed/gain ±SE

494 ± 23a 1.47 ± .03

B

495 ±12 1.46 ± .02

C

D

494 +7 1.47 ± .02

484 ±12 1.48 ± .01

'Differences among means were not statistically significant (P<.05).

Diet

TME (kcal/kg), air dry basis Calculated1 Determined

Determined/ calculated

A B C D

3360 3360 3360 3360

101.0 101.5 101.6 100.1

1

3395 3411 3414 3365

Calculated from the determined TME contents of individual feed ingredients.

energy c o n t e n t of t h e feed ingredients employed in this study. Results of the test of additivity of TME values are s h o w n in Table 7, t h e m a x i m u m difference b e t w e e n calculated and d e t e r m i n e d values being 1.6%. This confirms the earlier reports of Sibbald ( 1 9 7 7 a , b ) and Dale and Fuller ( 1 9 8 0 ) , in which a satisfactory additivity was also observed (Table 7). Differences in levels of fat inclusion in diets were t o o slight to p e r m i t a satisfactory test of t h e additivity of TME values for this ingredient. Horani a n d Sell ( 1 9 7 7 ) p o s t u l a t e d t h e existence of an " e x t r a metabolic effect" of fat, which suggests nonadditivity. It is of interest t o n o t e t h a t in t h e present s t u d y , t h e d e t e r m i n e d T M E of t h e three diets containing added fat were numerically, b u t n o t significantly, higher t h a n t h e calculated TME, while t h e determined and calculated TME's of diet D (with n o a d d e d fat) were virtually identical. U n d o u b t e d l y a p o r t i o n of t h e agreement in p e r f o r m a n c e parameters b e t w e e n diets is d u e t o t h e fact t h a t feeds were prepared using t h e same lots of ingredients t h a t had previously been assayed. Their isonitrogenous n a t u r e was t h u s assured. Under these conditions,

however, an accurate d e t e r m i n a t i o n of t h e available energy in all feedstuffs b e c a m e especially critical. It is concluded t h a t t h e TME system provided a highly satisfactory measure of t h e caloric c o n t e n t of t h e feedstuffs u s e d in this e x p e r i m e n t and t h a t values obtained using the assay are applicable t o broilers.

ACKNOWLEDGMENT This work was s u p p o r t e d in p a r t by a grant-in-aid from t h e F a t s and Proteins Research F o u n d a t i o n , Inc., Des Plaines, IL.

REFERENCES Dale, N. M., and H. L. Fuller, 1980. Additivity of true metabolizable energy values as measured with roosters, broiler chicks and poults. Poultry Sci. 59:1941-1942. Halloran, H. R., 1980. Comparison of metabolizable energy methods on identical ingredient samples. Poultry Sci. 59:1552-1553. Horani, F., and J. L. Sell, 1977. Effect of feed grade animal fat on laying hen performance and on metabolizable energy of rations. Poultry Sci. 56:1972-1980. Sibbald, I. R., 1976. Abioassay for true metabolizable energy in feedstuffs. Poultry Sci. 55:303-308. Sibbald, I. R., 1977a. A test of the additivity of true

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TABLE 7. Degree of additivity of TME values (Experiment 2)

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DALE AND FULLER

metabolizable energy values of feedstuffs. Poultry Sci. 56:363-366. Sibbald, I. R., 1977b. The "true metabolizable energy system" (Part II). Feedstuffs 49(43): 23-24. Snedecor, G. W., and W. G. Cochran, 1967. Statistical

methods. 6th ed. Iowa State Univ. Press, Ames, IA. Thomas, O. P., P. V. Twining, Jr., and E. H. Bossard, 1975. The amino acid and protein requirements for broilers. Pages 48—52 in Proc. Maryland. Nutr. Conf.

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