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True Metabolizable Energy Corrected to Nitrogen Equilibrium
True Metabolizable Energy Corrected to Nitrogen Equilibrium C. M. PARSONS,1 L. M. POTTER, and B. A. BLISS Department of Poultry Science, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 (Received for publication March 4, 1982)
1982 Poultry Science 61:2241-2246 INTRODUCTION Metabolizable energy of a diet is defined as its gross energy m i n u s t h e energy in feces and urine derived from t h e same q u a n t i t y of t h a t diet. T h e d e t e r m i n e d metabolizable energy of a diet m a y be c o n f o u n d e d b y t h e excretion of e n d o g e n o u s energy (metabolic fecal and e n d o genous u r i n a r y energy) t h a t was n o t derived directly from t h e diet u n d e r test. T o a c c o u n t for t h e latter, Sibbald ( 1 9 7 6 ) developed t h e t r u e m e t a b o l i z a b l e energy (TME) bioassay t h a t corrects t h e e x c r e t a energy for e n d o g e n o u s energy as measured w i t h a c c o m p a n y i n g fasted birds. Many studies have since been c o n d u c t e d t o evaluate t h e accuracy of this bioassay and t o measure t h e T M E of several diets and feed ingredients b y a d u l t roosters or other birds. A p o t e n t i a l p r o b l e m in t h e T M E bioassay b y Sibbald ( 1 9 7 7 ) involves t h e difference in t h e energy associated w i t h t h e loss of nitrogen b y t h e fasted b i r d s a n d t h e m u c h smaller loss or gain of nitrogen of t h e fed birds. E n d o g e n o u s nitrogen e x c r e t i o n b y fasted birds should be greater t h a n t h a t of fed birds d u e t o greater b r e a k d o w n of b o d y p r o t e i n t o m e e t energy
1
Department of Animal Science, University of Illinois, Urbana, IL 61801.
r e q u i r e m e n t s . As a result, t h e m e t a b o l i c fecal and e n d o g e n o u s urinary energy m e a s u r e d w i t h fasted birds in this T M E bioassay should theoretically provide a greater c o r r e c t i o n for e n d o g e n o u s energy t h a n justified. Therefore, t h e effects of t h e c o r r e c t i o n t o nitrogen equilibrium o n ME and TME d e t e r m i n a t i o n were e x a m i n e d in this s t u d y . EXPERIMENTAL PROCEDURE T w o replicate e x p e r i m e n t s using 18 h e n s and 12 roosters were c o n d u c t e d at a 2 - m o n t h interval. In each e x p e r i m e n t , adult Single C o m b White Leghorn roosters and laying hens were fasted for 2 4 hr. Each of five diets containing various p r o p o r t i o n s of a standard layer r a t i o n ( S L R ) and dehulled s o y b e a n meal (DSM) was t h e n force fed 30 g (dry m a t t e r basis) t o each of t h r e e hens and t w o roosters. In addition, a n o t h e r t h r e e hens and t w o roosters were fasted for an additional 4 8 h r t o o b t a i n m e a s u r e m e n t s of e n d o g e n o u s energy. T h e c o m p o s i t i o n of t h e S L R is presented in Table 1. T h e diets were mixed o n a dry m a t t e r basis and consisted of 100% SLR, 7 5 % SLR and 2 5 % DSM, 50% S L R and 50% DSM, 2 5 % S L R and 7 5 % DSM, and 100% DSM. T h e e x c r e t a of each bird were collected quantitatively from 0 t o 30 hr and from 30 t o 4 8 hr after feeding, dried t o c o n s t a n t weight a t
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ABSTRACT A study was conducted to examine the effects of the correction of excreta energy to nitrogen equilibrium in the determination of true metabolizable energy (TME). Roosters and laying hens were fed diets consisting of a standard layer ration blended with increasing amounts of dehulled soybean meal ranging from 0 to 100%. Dry matter digestibility, nitrogen retention, and apparent metabolizable energy were greater for females than the males. For males and females, dehulled soybean meal had values for dry matter digestibility of 50.1 and 52.0%, TME of 3.087 and 3.145 kcal/g dry matter, metabolizable energy corrected to nitrogen equilibrium (ME n ) of 2.683 and 2.719 kcal/g dry matter, and TME corrected to nitrogen equilibrium (TME n ) of 2.890 and 2.946 kcal/g dry matter, respectively. The differences between TME and TME n values were due to larger nitrogen losses from nondietary sources by fasted birds than by fed birds. Thus, the metabolic fecal and endogenous urinary energy as measured from the fasted birds provides a larger correction than justified for accurate TME determinations. The difference between the TME and the TME n in this study explains in part the previously reported abnormally high values for TME over ME n . Thus, ME n appears to be a more accurate measurement of metabolizable energy than TME. (Key words: true metabolizable energy, nitrogen-corrected true metabolizable energy)
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TABLE 1. Composition of standard layer ration
Ingredients
Total
535.5 100 50 25 25 30 50 80 20 4 70 5 .5 5 1,000.0
Supplied in milligrams per kilogram of diet: 60 manganese, 60 zinc, 20 iron, 2.5 copper, 1 iodine, .225 cobalt, and .2 selenium. Supplied per kilogram of diet: 5,500 IU vitamin A, 2,200 ICU vitamin D3 , 2.2 IU vitamin E, 3.5 mg menadione sodium bisulfite, 4.4 mg riboflavin, 11.0 mg calcium D-pantothenate, 33 mg niacin, 250 mg choline chloride, 6.6 Mg vitamin B 12 , .55 mg folic acid, 125 mg ethoxyquin, and 125 mg DL-methionine.
TME n = FEf - [EEf + 8.22 Nf ] + [EE U + 8.22 N u ] 65 C, ground to pass through a 60-mesh screen, and stored in tightly covered jars. Excreta of birds that regurgitated feed or of females that had broken eggs in excreta collection trays were discarded. Gross energy contents of the SLR, DSM, and excreta were determined with an adiabatic oxygen bomb calorimeter, and nitrogen contents were determined by the Kjeldahl method. Dry matter contents of the excreta were determined by redrying subsamples at 65 C for 24 hr to correct for moisture uptake during grinding. The average quantities of excreta dry matter collected between 30 and 48 hr postfeeding per bird did not vary significantly among treatments. From feeding nothing or diets containing 0, 25, 50, 75, or 100% SBM, males excreted 3.36, 3.03, 3.85, 2.72, 4.36, and 3.15 g, and females 2.28, 2.33, 2.43, 2.38, 2.68, and 2.50 g, respectively, with pooled standard errors of ±.61 and ±.36 g for males and females, respectively. Therefore, only the excreta collections gathered during the first 30 hr postfeeding were used in the TME determinations.
FC where FEf equals the gross energy of the total feed consumed; EEf and EE U equals the energy in the excreta collected from the fed birds and fasted birds, respectively; Nf and N u equals the g nitrogen retained by the fed birds and fasted birds, respectively; and FC equals the grams of dry feed consumed. No significant differences were observed between the replicate experiments. Therefore, the results of the two experiments were pooled for statistical analyses. Statistical analyses of the data included calculations of means and standard deviations of the measured dry matter, nitrogen, and nonmetabolizable energy in the excreta. Linear regressions of these measurements on levels of dehulled soybean meal used in the diets were calculated. RESULTS AND DISCUSSION Dry Matter. The fasted males and fasted females excreted 157 and 114 mg dry matter
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Ground yellow corn Pulverized oats Standard wheat middlings Wheat bran Dehydrated alfalfa meal Menhaden fish meal Meat and bone meal Dehulled soybean meal (49% protein) Stabilized fat Iodized salt Ground limestone Defluorinated phosphate Trace mineral mix a Vitamin and feed additive premix"
Composition (g/kg)
The quantities of dry matter excreted and retained by each bird were calculated from the analyses of the SLR, DSM, and excreta samples. The values for dry matter excreted were 1) corrected for the amount of excreta voided by the fasted birds, 2) corrected to nitrogen equilibrium assuming nitrogen gain or loss would produce 3 g dry matter per g of nitrogen (33.33% N in uric acid), and 3) corrected for both 1 and 2. The amounts of nitrogen consumed and excreted by each bird were calculated and averaged by diet and sex. The TME values of the diets were calculated by the method of Sibbald (1976). Particular attention was directed to the amount of excreta energy voided by each bird and the excreta energy corrected for metabolic fecal and endogenous urinary energy as measured from the fasted birds. The nonmetabolizable energy was corrected to nitrogen equilibrium assuming that nitrogen retained would produce additional urinary energy in the excreta amounting to 8.22 kcal/g nitrogen. These latter values were also corrected for endogenous energy of nonnitrogenous origin as measured from the fasted birds to obtain TME n . The TME n values were calculated by the equation:
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TME CORRECTED TO NITROGEN EQUILIBRIUM TABLE 2. Measurements of dry matter excretion during the 30-hr period postfeeding
Sex Males Fasted Fed
Females Fasted Fed
Dehulled soybean meal in diet (%)
Observations per mean
Uncorrected
0 25 50 75 100
4 3 3 3 4 3
4.71 ± 11.80+ 13.77+ 17.07 ± 18.02 ± 19.03 ±
1.36 d .90 .08 1.39 1.43 .28
7.09 9.06 12.36 13.31 14.32
1.57 ± 11.05 ± 12.75 + 15.91 ± 17.05 ± 18.17 +
.26 .68 .34 .82 .77 .89
9.48 11.18 14.34 15.48 16.60
0 25 50 75 100
4 5 5 6 5 4
3.41 + 9.79 ± 11.26 ± 14.27± 15.28 ± 18.02 ±
1.17 .72 1.74 1.42 .83 .70
6.38 7.85 10.86 11.87 14.61
1.98 ± 10.15 ± 12.07 + 14.60 ± 16.55 + 18.72 +
.90 .82 1.39 .93 .54 .70
8.17 10.09 12.62 14.57 16.74
Dry matter excreted (g) Corrected" Corrected a
Corrected 0
per hour (4.71 and 3.41 g during the 30-hr period), respectively (Table 2). These values are not significantly different from the 113 and 155 mg air-dry excreta per hour (2.72 and 3.73 g per day) obtained from fasted males in two experiments reported by Sibbald (1975). Large variation in dry matter excretion among fasted birds was observed in both our study and that of Sibbald (1975). The average amount of dry matter excreted by the fed birds was 2.22 g (15.94 minus 13.72 g) greater among males than among females. This difference was apparently not due to the greater body weight of males than females, which averaged 1.91 and 1.82 kg, respectively. As expected, the amount of dry matter excreted increased as the level of DSM in the diet increased, indicating that the dry matter digestibility of the DSM was much less than that of the SLR. Assuming that the dry matter excreted by the fasted birds is a measure of endogenous dry matter for the fed birds, the amount of excreta derived from each diet was calculated. From a
2 Calculated as follows: [30.00 - 14.411/30.00 = .520 or 52.0%.
regression o f Y = b i X ! + b 2 X 2 where Y equals the quantity of dry matter excreted corrected for endogenous dry matter and Xi and X 2 equals the decimal portion of SLR and DSM in the diet, respectively, the following equations with standard errors were obtained: Y = 7.49 Xj + 14.97 X 2 for males and (±.63) (±.63) Y = 6.19 Xi + 14.41 X 2 for females. (+.40) (±.40) Based on this assumption, the dry matter in the SLR was 75.0 and 79.3% digested, and the dry matter in the DSM was 50.1 and 52.0% 2 digested by males and females, respectively. A greater dry matter digestibility of the SLR by females may be expected as a result of added deposition of calcium carbonate in the egg by the females. Pierson et al. (1980) reported that the dry matter in DSM was 5 3.3% digested by male turkeys, a value similar to that obtained for adult chickens in this study. The values for dry matter excreted were also corrected to nitrogen equilibrium assuming that the nitrogen retained or lost during metabolism would produce urinary products composed of one-third nitrogen on a dry matter basis. This
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Corrected for metabolic fecal and endogenous urinary dry matter as measured with fasted birds. Corrected for nitrogen retention assuming that nitrogen retained or lost would yield urinary products containing 33.3% nitrogen on a dry matter basis. c Corrected for both a and b. Mean + standard deviation per bird.
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0
.5
1.0
1.5
2.0
2.5
3.0
NITROGEN CONSUMED, G FIG. 1. Amount of nitrogen excreted by birds during the 30 hr postfeeding period plotted on nitrogen consumed at time of force feeding.
males and females, it is apparent that TME and ME values should be corrected to nitrogen equilibrium, a point raised by Muztar and Slinger(1981). Excreta Energy. The measurements of energy in excreta per gram of dry diet consumed by males and females fed each diet are presented in Table 4. More energy was excreted per gram of dry diet consumed by males than by females.
TABLE 3. Total nitrogen consumed and excreted during the 30-hr period postfeeding Dehulled soybean meal in diet (%)
Sex Males Fasted Fed
Females Fasted Fed
0 25 50 75 100
Nitrogen (g) Consumed
Excreted
0
1.049 ± 1.103 ± 1.637 ± 2.129 ± 2.518* 2.928 ±
.849 1.296 1.744 2.191 2.638 0
0 25 50 75 100
Mean ± standard deviation per bird.
.849 1.296 1.744 2.191 2.638
.453 .728 1.028 1.637 1.767 2.507
.374a .085 .087 .299 .335 .319
± .174 ± .202 ±.254 ± .281 ± .143 ± .272
Retained
-1.049 -.254 -.341 -.385 -.327 -.290 -.453 .121 .268 .107 .424 .131
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correction accounted for 67 and 42% of the dry matter excreted by the fasted males and females, respectively. Nitrogen. The measurements of nitrogen consumed, excreted, and retained by the males and females fed each diet are presented in Table 3. The fasted males and fasted females excreted 1.049 and .453 g nitrogen, respectively, during the 30-hr period or the equivalent of 35 and 15 mg nitrogen per hour. These values may be compared to .375 g nitrogen reported by Sibbald (1975) and .599 g nitrogen reported by Shires et al. (1980) for fasted males during a 24-hr period or 16 and 25 mg nitrogen per hour, respectively. These differences indicate that the excretion of nitrogen by fasted birds varies considerably. The females fed the various diets in this study were in positive nitrogen balance whereas the males were in negative nitrogen balance (Fig. 1). Based upon data published by Sibbald (1975) and Shires et al. (1980), feed intake providing .8 to 1.0 g of nitrogen per day from wheat or corn was sufficient to place roosters in a positive nitrogen balance. A similar positive balance was obtained for the females in this study, but males were found to be in slight negative balance when fed diets containing as much as 2.7 g of nitrogen per day. The greater nitrogen retention for females than for males was probably due to the deposition of nitrogen in eggs laid by females. Because of the variation in nitrogen balance between
TME CORRECTED TO NITROGEN EQUILIBRIUM
Y = .655 X] + 1.749 X 2 for males and (±.068) (±.068) Y = .600 Xj + 1.689 X 2 for females. (±.036) (±.036)
Based on a gross energy of 4.268 and 4.834 kcal/g dry matter for the SLR and the DSM, respectively, the TME values were 3.613 and 3.668 kcal/g dry matter for the SLR and 3.087 and 3.145 kcal/g dry matter for the DSM from males and females, respectively. The latter values are within the range of 3.00 to 3.40 kcal/g dry matter reported by Sibbald (1977) for soybean meal containing 49% protein. However, these values are considerably greater than the metabolizable energy of dehulled soybean meal (50% protein) obtained by Hill and Renner (1960) of 2.77 (range of 2.38 to 2.99) kcal/g dry matter, by Potter and Matterson (1960) of 2.67 (range of 2.52 to 2.79) kcal/g dry matter, and by Sibbald and Slinger (1962) of 2.73 kcal/g dry matter. When the excreta values in kilocalories per gram dry matter were corrected to nitrogen equilibrium, no difference was observed in metabolizable energy for any diet between males and females. Because the males had a net nitrogen loss and females a net nitrogen gain during the experiment, the nitrogen correction decreased the estimated excreta energy of males but increased the estimated excreta
TABLE 4. Measurements of energy in the excreta collected during 30-hr postfeeding Dehulled soybean meal in diet (%)
Observation per mean
Energy in excreta (kcal/g dry diet consumed) Corrected* Corrected 0 Corrected 0 Uncorrected
Males
0 25 50 75 100
3 3 3 4 3
1.135+ 1.356 ± 1.822 ± 1.967 + 2.194 ±
.094 d .044 .148 .103 .046
.641 .862 1.328 1.473 1.700
1.066 1.263 1.717 1.878 2.116
± ± ± ± ±
.07 2 d .021 .138 .092 .107
.859 1.056 1.510 1.671 1.909
Females
0 25 50 75 100
5 5 6 5 4
.998 1.199 1.491 1.734 2.092
.057 .184 .191 .157 .106
.640 .841 1.133 1.376 1.734
1.033 1.273 1.521 1.850 2.129
± ± t ± ±
.070 .180 .168 .134 .113
.806 1.046 1.294 1.623 1.902
Sex
± ± ± ± ±
Corrected for metabolic fecal and endogenous urinary dry matter as measured with fasted birds. Fasted males and fasted females excreted 14.82 and 10.74 kcal, respectively, which accounts for the respective .494 ± .162 and .358 ± .091 kcal/g dry diet correction at 30 g feed consumption. Corrected for nitrogen retention or to nitrogen equilibrium assuming that the nitrogen retained would produce additional urinary energy amounting to 8.22 kcal energy per gram nitrogen to the excreta. The fasted males and fasted females excreted 8.62 and 3.93 kcal of energy, respectively, which amounted to the respective .287 and .131 kcal/g dry diet correction if applied to a 30 g feed consumption. Values in previous column corrected for additional metabolic fecal and endogenous urinary energy not of nitrogen origin as measured for fasted birds. Fasted males and fasted females excreted an estimated 6.20 and 6.81 kcal of energy, respectively, which accounts for the respective .207 ± .069 and .227 + .083 kcal/g dry diet corrected at 30 g feed consumption. Mean + standard deviation per bird.
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More energy was also excreted by the fasted males than by the fasted females during the 30-hr collection period or 14.82 and 10.74 kcal per male and female, respectively. The fasted males weighed 1.92 kg and the fasted females weighed 1.90 kg; thus, the greater energy excreted by the fasted males was not a function of body size. When excreta energy values in kilocalories per gram dry diet were corrected for the endogenous energy obtained with fasted birds, differences between males and females were nonsignificant. Based on the 30-g feed consumptions, the corrections were .494 and .358 kcal/g dry diet for males and females, respectively. Regressions with the model Y = b ] X i + b 2 X 2 when Y equals the corrected excreta energy, and X] and X 2 equals the decimal portion of SLR and DSM, respectively, in the diets produced the following equations and standard errors:
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energy of females. Regressions with the model Y = b i X ! + b 2 X 2 where Y equals the excreta energy corrected to nitrogen equilibrium, and Xi and X 2 equal the decimal portion of SLR and DSM in the diets produced the following equations and standard errors: Y = 1.065 Xj +2.151 X 2 for males and (+.061) (+.061) Y = 1.007 Xj + 2.115 X 2 for females. (+.023) (±.023)
.297+1.013X for males and (+.074) (+.040)
Y = - . 1 4 2 + .961X for females. (±.201) (±.109) The fasted birds were in greater negative balance (Fig. 1) than the Y-intercepts showed. Thus, energy excreted by fasted birds overestimates excretion of endogenous energy by fed birds and results in an erroneously large correction in the calculation of TME values. These observations partially explain the abnormally large difference between TME values and conventional ME n values. The results of this study lead one to question the reliability of the TME determination. The larger correction in metabolic fecal and endogenous urinary energy than justified is evident by the greater nitrogen lost by fasted birds than from nondietary sources by fed birds. We conclude that ME n is a more accurate measurement of metabolizable energy than is TME. ACKNOWLEDGMENTS This study was supported by a grant from the John Lee Pratt Animal Nutrition Program at Virginia Polytechnic Institute and State University, Blacksburg, VA. REFERENCES Hill, F. W., and R. Renner, 1960. The metabolizable energy of soybean oil meals, soybean millfeeds and soybean hulls for the growing chick. Poultry Sci. 39:579-583. Muztar, A. J., and S. J. Slinger, 1981. An evaluation of the nitrogen correction in the true metabolizable energy assay. Poultry Sci. 60:835—839. Pierson, E.E.M., L. M. Potter, and R. D. Brown, Jr., 1980. Amino acid digestibility of dehulled soybean meal by adult turkeys. Poultry Sci. 59:845-848. Potter, L. M., and L. D. Matterson, 1960. Metabolizable energy of feed ingredients for the growing chick. Poultry Sci. 39:781-782. Sibbald, I. R., 1975. The effect of level of feed intake on metabolizable energy values measured with adult roosters. Poultry Sci. 54:1990-1997. Sibbald, I. R. 1976. A bioassay for true metabolizable energy in feedingstuffs. Poultry Sci. 55:303—308. Sibbald, I. R., 1977. The true metabolizable energy values of some feedingstuffs. Poultry Sci. 56:380-382. Sibbald, I. R., and S. J. Slinger, 1962. The metabolizable energy of materials fed to growing chicks. Poultry Sci. 41:1612-1613. Shires, A., A. R. Robblee, R. T. Hardin, and D. R. Clandinin, 1980. Effect of the age of chickens on the true metabolizable energy values of feed ingredients. Poultry Sci. 59:396-403.
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The values for metabolizable energy corrected to nitrogen equilibrium (ME n ) were 3.203 and 3.261 kcal/g dry matter for the SLR and 2.683 and 2.719 kcal/g dry matter for the DSM from males and females, respectively. These values for DSM are similar to those reported by Hill and Renner (1960), Potter and Matterson (1960), and Sibbald and Slinger (1962) for DSM (50% protein), but are much lower than the TME values reported by Sibbald (1977) for DSM containing 49% protein. Values for excreta energy corrected for both energy associated with nitrogen gain or loss (nitrogen equilibrium) and nonnitrogenous endogenous end-products are also presented in Table 4. The nonnitrogenous energy from endogenous sources measured by fasted male and fasted female birds were .207 and .227 kcal/g dry diet, respectively. Thus, energy associated with nitrogen excretion accounts for 37 and 58% of the total energy excreted by fasted males and females, respectively. By regression, the TME n values were 3.410 and 3.488 kcal/g dry matter for the SLR and 2.890 and 2.946 kcal/g dry matter for DSM with males and females, respectively. Thus, the TME n values were approximately .20 kcal/g lower than the uncorrected TME values. These results are in contrast to those reported by Muztar and Slinger (1981); however, they applied the nitrogen correction to only the fed birds and not to the fasted birds in their TME n calculations. This difference explains the variation between the results of Muztar and Slinger (1981) and those of the present study. The lower values for TME n as compared to TME are apparently due to greater excretion of nondietary nitrogen by fasted birds than by fed birds (Fig. 1). This conclusion is further supported by regressions of quantity of nitrogen excreted (Y) on that consumed (X) by fed birds (data from fasted birds omitted) to produce the equations:
Y=
1982 Poultry Science 61:2241-2246 INTRODUCTION Metabolizable energy of a diet is defined as its gross energy m i n u s t h e energy in feces and urine derived from t h e same q u a n t i t y of t h a t diet. T h e d e t e r m i n e d metabolizable energy of a diet m a y be c o n f o u n d e d b y t h e excretion of e n d o g e n o u s energy (metabolic fecal and e n d o genous u r i n a r y energy) t h a t was n o t derived directly from t h e diet u n d e r test. T o a c c o u n t for t h e latter, Sibbald ( 1 9 7 6 ) developed t h e t r u e m e t a b o l i z a b l e energy (TME) bioassay t h a t corrects t h e e x c r e t a energy for e n d o g e n o u s energy as measured w i t h a c c o m p a n y i n g fasted birds. Many studies have since been c o n d u c t e d t o evaluate t h e accuracy of this bioassay and t o measure t h e T M E of several diets and feed ingredients b y a d u l t roosters or other birds. A p o t e n t i a l p r o b l e m in t h e T M E bioassay b y Sibbald ( 1 9 7 7 ) involves t h e difference in t h e energy associated w i t h t h e loss of nitrogen b y t h e fasted b i r d s a n d t h e m u c h smaller loss or gain of nitrogen of t h e fed birds. E n d o g e n o u s nitrogen e x c r e t i o n b y fasted birds should be greater t h a n t h a t of fed birds d u e t o greater b r e a k d o w n of b o d y p r o t e i n t o m e e t energy
1
Department of Animal Science, University of Illinois, Urbana, IL 61801.
r e q u i r e m e n t s . As a result, t h e m e t a b o l i c fecal and e n d o g e n o u s urinary energy m e a s u r e d w i t h fasted birds in this T M E bioassay should theoretically provide a greater c o r r e c t i o n for e n d o g e n o u s energy t h a n justified. Therefore, t h e effects of t h e c o r r e c t i o n t o nitrogen equilibrium o n ME and TME d e t e r m i n a t i o n were e x a m i n e d in this s t u d y . EXPERIMENTAL PROCEDURE T w o replicate e x p e r i m e n t s using 18 h e n s and 12 roosters were c o n d u c t e d at a 2 - m o n t h interval. In each e x p e r i m e n t , adult Single C o m b White Leghorn roosters and laying hens were fasted for 2 4 hr. Each of five diets containing various p r o p o r t i o n s of a standard layer r a t i o n ( S L R ) and dehulled s o y b e a n meal (DSM) was t h e n force fed 30 g (dry m a t t e r basis) t o each of t h r e e hens and t w o roosters. In addition, a n o t h e r t h r e e hens and t w o roosters were fasted for an additional 4 8 h r t o o b t a i n m e a s u r e m e n t s of e n d o g e n o u s energy. T h e c o m p o s i t i o n of t h e S L R is presented in Table 1. T h e diets were mixed o n a dry m a t t e r basis and consisted of 100% SLR, 7 5 % SLR and 2 5 % DSM, 50% S L R and 50% DSM, 2 5 % S L R and 7 5 % DSM, and 100% DSM. T h e e x c r e t a of each bird were collected quantitatively from 0 t o 30 hr and from 30 t o 4 8 hr after feeding, dried t o c o n s t a n t weight a t
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ABSTRACT A study was conducted to examine the effects of the correction of excreta energy to nitrogen equilibrium in the determination of true metabolizable energy (TME). Roosters and laying hens were fed diets consisting of a standard layer ration blended with increasing amounts of dehulled soybean meal ranging from 0 to 100%. Dry matter digestibility, nitrogen retention, and apparent metabolizable energy were greater for females than the males. For males and females, dehulled soybean meal had values for dry matter digestibility of 50.1 and 52.0%, TME of 3.087 and 3.145 kcal/g dry matter, metabolizable energy corrected to nitrogen equilibrium (ME n ) of 2.683 and 2.719 kcal/g dry matter, and TME corrected to nitrogen equilibrium (TME n ) of 2.890 and 2.946 kcal/g dry matter, respectively. The differences between TME and TME n values were due to larger nitrogen losses from nondietary sources by fasted birds than by fed birds. Thus, the metabolic fecal and endogenous urinary energy as measured from the fasted birds provides a larger correction than justified for accurate TME determinations. The difference between the TME and the TME n in this study explains in part the previously reported abnormally high values for TME over ME n . Thus, ME n appears to be a more accurate measurement of metabolizable energy than TME. (Key words: true metabolizable energy, nitrogen-corrected true metabolizable energy)
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TABLE 1. Composition of standard layer ration
Ingredients
Total
535.5 100 50 25 25 30 50 80 20 4 70 5 .5 5 1,000.0
Supplied in milligrams per kilogram of diet: 60 manganese, 60 zinc, 20 iron, 2.5 copper, 1 iodine, .225 cobalt, and .2 selenium. Supplied per kilogram of diet: 5,500 IU vitamin A, 2,200 ICU vitamin D3 , 2.2 IU vitamin E, 3.5 mg menadione sodium bisulfite, 4.4 mg riboflavin, 11.0 mg calcium D-pantothenate, 33 mg niacin, 250 mg choline chloride, 6.6 Mg vitamin B 12 , .55 mg folic acid, 125 mg ethoxyquin, and 125 mg DL-methionine.
TME n = FEf - [EEf + 8.22 Nf ] + [EE U + 8.22 N u ] 65 C, ground to pass through a 60-mesh screen, and stored in tightly covered jars. Excreta of birds that regurgitated feed or of females that had broken eggs in excreta collection trays were discarded. Gross energy contents of the SLR, DSM, and excreta were determined with an adiabatic oxygen bomb calorimeter, and nitrogen contents were determined by the Kjeldahl method. Dry matter contents of the excreta were determined by redrying subsamples at 65 C for 24 hr to correct for moisture uptake during grinding. The average quantities of excreta dry matter collected between 30 and 48 hr postfeeding per bird did not vary significantly among treatments. From feeding nothing or diets containing 0, 25, 50, 75, or 100% SBM, males excreted 3.36, 3.03, 3.85, 2.72, 4.36, and 3.15 g, and females 2.28, 2.33, 2.43, 2.38, 2.68, and 2.50 g, respectively, with pooled standard errors of ±.61 and ±.36 g for males and females, respectively. Therefore, only the excreta collections gathered during the first 30 hr postfeeding were used in the TME determinations.
FC where FEf equals the gross energy of the total feed consumed; EEf and EE U equals the energy in the excreta collected from the fed birds and fasted birds, respectively; Nf and N u equals the g nitrogen retained by the fed birds and fasted birds, respectively; and FC equals the grams of dry feed consumed. No significant differences were observed between the replicate experiments. Therefore, the results of the two experiments were pooled for statistical analyses. Statistical analyses of the data included calculations of means and standard deviations of the measured dry matter, nitrogen, and nonmetabolizable energy in the excreta. Linear regressions of these measurements on levels of dehulled soybean meal used in the diets were calculated. RESULTS AND DISCUSSION Dry Matter. The fasted males and fasted females excreted 157 and 114 mg dry matter
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Ground yellow corn Pulverized oats Standard wheat middlings Wheat bran Dehydrated alfalfa meal Menhaden fish meal Meat and bone meal Dehulled soybean meal (49% protein) Stabilized fat Iodized salt Ground limestone Defluorinated phosphate Trace mineral mix a Vitamin and feed additive premix"
Composition (g/kg)
The quantities of dry matter excreted and retained by each bird were calculated from the analyses of the SLR, DSM, and excreta samples. The values for dry matter excreted were 1) corrected for the amount of excreta voided by the fasted birds, 2) corrected to nitrogen equilibrium assuming nitrogen gain or loss would produce 3 g dry matter per g of nitrogen (33.33% N in uric acid), and 3) corrected for both 1 and 2. The amounts of nitrogen consumed and excreted by each bird were calculated and averaged by diet and sex. The TME values of the diets were calculated by the method of Sibbald (1976). Particular attention was directed to the amount of excreta energy voided by each bird and the excreta energy corrected for metabolic fecal and endogenous urinary energy as measured from the fasted birds. The nonmetabolizable energy was corrected to nitrogen equilibrium assuming that nitrogen retained would produce additional urinary energy in the excreta amounting to 8.22 kcal/g nitrogen. These latter values were also corrected for endogenous energy of nonnitrogenous origin as measured from the fasted birds to obtain TME n . The TME n values were calculated by the equation:
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TME CORRECTED TO NITROGEN EQUILIBRIUM TABLE 2. Measurements of dry matter excretion during the 30-hr period postfeeding
Sex Males Fasted Fed
Females Fasted Fed
Dehulled soybean meal in diet (%)
Observations per mean
Uncorrected
0 25 50 75 100
4 3 3 3 4 3
4.71 ± 11.80+ 13.77+ 17.07 ± 18.02 ± 19.03 ±
1.36 d .90 .08 1.39 1.43 .28
7.09 9.06 12.36 13.31 14.32
1.57 ± 11.05 ± 12.75 + 15.91 ± 17.05 ± 18.17 +
.26 .68 .34 .82 .77 .89
9.48 11.18 14.34 15.48 16.60
0 25 50 75 100
4 5 5 6 5 4
3.41 + 9.79 ± 11.26 ± 14.27± 15.28 ± 18.02 ±
1.17 .72 1.74 1.42 .83 .70
6.38 7.85 10.86 11.87 14.61
1.98 ± 10.15 ± 12.07 + 14.60 ± 16.55 + 18.72 +
.90 .82 1.39 .93 .54 .70
8.17 10.09 12.62 14.57 16.74
Dry matter excreted (g) Corrected" Corrected a
Corrected 0
per hour (4.71 and 3.41 g during the 30-hr period), respectively (Table 2). These values are not significantly different from the 113 and 155 mg air-dry excreta per hour (2.72 and 3.73 g per day) obtained from fasted males in two experiments reported by Sibbald (1975). Large variation in dry matter excretion among fasted birds was observed in both our study and that of Sibbald (1975). The average amount of dry matter excreted by the fed birds was 2.22 g (15.94 minus 13.72 g) greater among males than among females. This difference was apparently not due to the greater body weight of males than females, which averaged 1.91 and 1.82 kg, respectively. As expected, the amount of dry matter excreted increased as the level of DSM in the diet increased, indicating that the dry matter digestibility of the DSM was much less than that of the SLR. Assuming that the dry matter excreted by the fasted birds is a measure of endogenous dry matter for the fed birds, the amount of excreta derived from each diet was calculated. From a
2 Calculated as follows: [30.00 - 14.411/30.00 = .520 or 52.0%.
regression o f Y = b i X ! + b 2 X 2 where Y equals the quantity of dry matter excreted corrected for endogenous dry matter and Xi and X 2 equals the decimal portion of SLR and DSM in the diet, respectively, the following equations with standard errors were obtained: Y = 7.49 Xj + 14.97 X 2 for males and (±.63) (±.63) Y = 6.19 Xi + 14.41 X 2 for females. (+.40) (±.40) Based on this assumption, the dry matter in the SLR was 75.0 and 79.3% digested, and the dry matter in the DSM was 50.1 and 52.0% 2 digested by males and females, respectively. A greater dry matter digestibility of the SLR by females may be expected as a result of added deposition of calcium carbonate in the egg by the females. Pierson et al. (1980) reported that the dry matter in DSM was 5 3.3% digested by male turkeys, a value similar to that obtained for adult chickens in this study. The values for dry matter excreted were also corrected to nitrogen equilibrium assuming that the nitrogen retained or lost during metabolism would produce urinary products composed of one-third nitrogen on a dry matter basis. This
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Corrected for metabolic fecal and endogenous urinary dry matter as measured with fasted birds. Corrected for nitrogen retention assuming that nitrogen retained or lost would yield urinary products containing 33.3% nitrogen on a dry matter basis. c Corrected for both a and b. Mean + standard deviation per bird.
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PARSONS ET AL.
0
.5
1.0
1.5
2.0
2.5
3.0
NITROGEN CONSUMED, G FIG. 1. Amount of nitrogen excreted by birds during the 30 hr postfeeding period plotted on nitrogen consumed at time of force feeding.
males and females, it is apparent that TME and ME values should be corrected to nitrogen equilibrium, a point raised by Muztar and Slinger(1981). Excreta Energy. The measurements of energy in excreta per gram of dry diet consumed by males and females fed each diet are presented in Table 4. More energy was excreted per gram of dry diet consumed by males than by females.
TABLE 3. Total nitrogen consumed and excreted during the 30-hr period postfeeding Dehulled soybean meal in diet (%)
Sex Males Fasted Fed
Females Fasted Fed
0 25 50 75 100
Nitrogen (g) Consumed
Excreted
0
1.049 ± 1.103 ± 1.637 ± 2.129 ± 2.518* 2.928 ±
.849 1.296 1.744 2.191 2.638 0
0 25 50 75 100
Mean ± standard deviation per bird.
.849 1.296 1.744 2.191 2.638
.453 .728 1.028 1.637 1.767 2.507
.374a .085 .087 .299 .335 .319
± .174 ± .202 ±.254 ± .281 ± .143 ± .272
Retained
-1.049 -.254 -.341 -.385 -.327 -.290 -.453 .121 .268 .107 .424 .131
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correction accounted for 67 and 42% of the dry matter excreted by the fasted males and females, respectively. Nitrogen. The measurements of nitrogen consumed, excreted, and retained by the males and females fed each diet are presented in Table 3. The fasted males and fasted females excreted 1.049 and .453 g nitrogen, respectively, during the 30-hr period or the equivalent of 35 and 15 mg nitrogen per hour. These values may be compared to .375 g nitrogen reported by Sibbald (1975) and .599 g nitrogen reported by Shires et al. (1980) for fasted males during a 24-hr period or 16 and 25 mg nitrogen per hour, respectively. These differences indicate that the excretion of nitrogen by fasted birds varies considerably. The females fed the various diets in this study were in positive nitrogen balance whereas the males were in negative nitrogen balance (Fig. 1). Based upon data published by Sibbald (1975) and Shires et al. (1980), feed intake providing .8 to 1.0 g of nitrogen per day from wheat or corn was sufficient to place roosters in a positive nitrogen balance. A similar positive balance was obtained for the females in this study, but males were found to be in slight negative balance when fed diets containing as much as 2.7 g of nitrogen per day. The greater nitrogen retention for females than for males was probably due to the deposition of nitrogen in eggs laid by females. Because of the variation in nitrogen balance between
TME CORRECTED TO NITROGEN EQUILIBRIUM
Y = .655 X] + 1.749 X 2 for males and (±.068) (±.068) Y = .600 Xj + 1.689 X 2 for females. (±.036) (±.036)
Based on a gross energy of 4.268 and 4.834 kcal/g dry matter for the SLR and the DSM, respectively, the TME values were 3.613 and 3.668 kcal/g dry matter for the SLR and 3.087 and 3.145 kcal/g dry matter for the DSM from males and females, respectively. The latter values are within the range of 3.00 to 3.40 kcal/g dry matter reported by Sibbald (1977) for soybean meal containing 49% protein. However, these values are considerably greater than the metabolizable energy of dehulled soybean meal (50% protein) obtained by Hill and Renner (1960) of 2.77 (range of 2.38 to 2.99) kcal/g dry matter, by Potter and Matterson (1960) of 2.67 (range of 2.52 to 2.79) kcal/g dry matter, and by Sibbald and Slinger (1962) of 2.73 kcal/g dry matter. When the excreta values in kilocalories per gram dry matter were corrected to nitrogen equilibrium, no difference was observed in metabolizable energy for any diet between males and females. Because the males had a net nitrogen loss and females a net nitrogen gain during the experiment, the nitrogen correction decreased the estimated excreta energy of males but increased the estimated excreta
TABLE 4. Measurements of energy in the excreta collected during 30-hr postfeeding Dehulled soybean meal in diet (%)
Observation per mean
Energy in excreta (kcal/g dry diet consumed) Corrected* Corrected 0 Corrected 0 Uncorrected
Males
0 25 50 75 100
3 3 3 4 3
1.135+ 1.356 ± 1.822 ± 1.967 + 2.194 ±
.094 d .044 .148 .103 .046
.641 .862 1.328 1.473 1.700
1.066 1.263 1.717 1.878 2.116
± ± ± ± ±
.07 2 d .021 .138 .092 .107
.859 1.056 1.510 1.671 1.909
Females
0 25 50 75 100
5 5 6 5 4
.998 1.199 1.491 1.734 2.092
.057 .184 .191 .157 .106
.640 .841 1.133 1.376 1.734
1.033 1.273 1.521 1.850 2.129
± ± t ± ±
.070 .180 .168 .134 .113
.806 1.046 1.294 1.623 1.902
Sex
± ± ± ± ±
Corrected for metabolic fecal and endogenous urinary dry matter as measured with fasted birds. Fasted males and fasted females excreted 14.82 and 10.74 kcal, respectively, which accounts for the respective .494 ± .162 and .358 ± .091 kcal/g dry diet correction at 30 g feed consumption. Corrected for nitrogen retention or to nitrogen equilibrium assuming that the nitrogen retained would produce additional urinary energy amounting to 8.22 kcal energy per gram nitrogen to the excreta. The fasted males and fasted females excreted 8.62 and 3.93 kcal of energy, respectively, which amounted to the respective .287 and .131 kcal/g dry diet correction if applied to a 30 g feed consumption. Values in previous column corrected for additional metabolic fecal and endogenous urinary energy not of nitrogen origin as measured for fasted birds. Fasted males and fasted females excreted an estimated 6.20 and 6.81 kcal of energy, respectively, which accounts for the respective .207 ± .069 and .227 + .083 kcal/g dry diet corrected at 30 g feed consumption. Mean + standard deviation per bird.
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More energy was also excreted by the fasted males than by the fasted females during the 30-hr collection period or 14.82 and 10.74 kcal per male and female, respectively. The fasted males weighed 1.92 kg and the fasted females weighed 1.90 kg; thus, the greater energy excreted by the fasted males was not a function of body size. When excreta energy values in kilocalories per gram dry diet were corrected for the endogenous energy obtained with fasted birds, differences between males and females were nonsignificant. Based on the 30-g feed consumptions, the corrections were .494 and .358 kcal/g dry diet for males and females, respectively. Regressions with the model Y = b ] X i + b 2 X 2 when Y equals the corrected excreta energy, and X] and X 2 equals the decimal portion of SLR and DSM, respectively, in the diets produced the following equations and standard errors:
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PARSONS ET AL.
energy of females. Regressions with the model Y = b i X ! + b 2 X 2 where Y equals the excreta energy corrected to nitrogen equilibrium, and Xi and X 2 equal the decimal portion of SLR and DSM in the diets produced the following equations and standard errors: Y = 1.065 Xj +2.151 X 2 for males and (+.061) (+.061) Y = 1.007 Xj + 2.115 X 2 for females. (+.023) (±.023)
.297+1.013X for males and (+.074) (+.040)
Y = - . 1 4 2 + .961X for females. (±.201) (±.109) The fasted birds were in greater negative balance (Fig. 1) than the Y-intercepts showed. Thus, energy excreted by fasted birds overestimates excretion of endogenous energy by fed birds and results in an erroneously large correction in the calculation of TME values. These observations partially explain the abnormally large difference between TME values and conventional ME n values. The results of this study lead one to question the reliability of the TME determination. The larger correction in metabolic fecal and endogenous urinary energy than justified is evident by the greater nitrogen lost by fasted birds than from nondietary sources by fed birds. We conclude that ME n is a more accurate measurement of metabolizable energy than is TME. ACKNOWLEDGMENTS This study was supported by a grant from the John Lee Pratt Animal Nutrition Program at Virginia Polytechnic Institute and State University, Blacksburg, VA. REFERENCES Hill, F. W., and R. Renner, 1960. The metabolizable energy of soybean oil meals, soybean millfeeds and soybean hulls for the growing chick. Poultry Sci. 39:579-583. Muztar, A. J., and S. J. Slinger, 1981. An evaluation of the nitrogen correction in the true metabolizable energy assay. Poultry Sci. 60:835—839. Pierson, E.E.M., L. M. Potter, and R. D. Brown, Jr., 1980. Amino acid digestibility of dehulled soybean meal by adult turkeys. Poultry Sci. 59:845-848. Potter, L. M., and L. D. Matterson, 1960. Metabolizable energy of feed ingredients for the growing chick. Poultry Sci. 39:781-782. Sibbald, I. R., 1975. The effect of level of feed intake on metabolizable energy values measured with adult roosters. Poultry Sci. 54:1990-1997. Sibbald, I. R. 1976. A bioassay for true metabolizable energy in feedingstuffs. Poultry Sci. 55:303—308. Sibbald, I. R., 1977. The true metabolizable energy values of some feedingstuffs. Poultry Sci. 56:380-382. Sibbald, I. R., and S. J. Slinger, 1962. The metabolizable energy of materials fed to growing chicks. Poultry Sci. 41:1612-1613. Shires, A., A. R. Robblee, R. T. Hardin, and D. R. Clandinin, 1980. Effect of the age of chickens on the true metabolizable energy values of feed ingredients. Poultry Sci. 59:396-403.
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The values for metabolizable energy corrected to nitrogen equilibrium (ME n ) were 3.203 and 3.261 kcal/g dry matter for the SLR and 2.683 and 2.719 kcal/g dry matter for the DSM from males and females, respectively. These values for DSM are similar to those reported by Hill and Renner (1960), Potter and Matterson (1960), and Sibbald and Slinger (1962) for DSM (50% protein), but are much lower than the TME values reported by Sibbald (1977) for DSM containing 49% protein. Values for excreta energy corrected for both energy associated with nitrogen gain or loss (nitrogen equilibrium) and nonnitrogenous endogenous end-products are also presented in Table 4. The nonnitrogenous energy from endogenous sources measured by fasted male and fasted female birds were .207 and .227 kcal/g dry diet, respectively. Thus, energy associated with nitrogen excretion accounts for 37 and 58% of the total energy excreted by fasted males and females, respectively. By regression, the TME n values were 3.410 and 3.488 kcal/g dry matter for the SLR and 2.890 and 2.946 kcal/g dry matter for DSM with males and females, respectively. Thus, the TME n values were approximately .20 kcal/g lower than the uncorrected TME values. These results are in contrast to those reported by Muztar and Slinger (1981); however, they applied the nitrogen correction to only the fed birds and not to the fasted birds in their TME n calculations. This difference explains the variation between the results of Muztar and Slinger (1981) and those of the present study. The lower values for TME n as compared to TME are apparently due to greater excretion of nondietary nitrogen by fasted birds than by fed birds (Fig. 1). This conclusion is further supported by regressions of quantity of nitrogen excreted (Y) on that consumed (X) by fed birds (data from fasted birds omitted) to produce the equations:
Y=