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A Modified Voluntary Feed Intake Bioassay for Determination of Metabolizable Energy with Leghorn Roosters
A Modified Voluntary Feed Intake Bioassay for Determination of Metabolizable Energy with Leghorn Roosters C. M. PARSONS,1 L. M. POTTER, 2 and B. A. BLISS Department of Poultry Science, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 (Received for publication March 4, 1983)
1984 Poultry Science 63:1610-1616 INTRODUCTION Sibbald (1976) described a rapid and simple method for the determination of true metabolizable energy (TME) of feedstuffs for poultry. Test ingredients are force-fed as the sole dietary component, and excreta are collected quantitatively for 48 hr (Sibbald, 1979). The TME values are calculated by correcting energy excreted for that which is of metabolic and endogenous origin. Metabolic and endogenous energy is measured by energy excretion of separate fasted birds during the trial. Although rapid, the procedure of Sibbald (1976) has some disadvantages. Force-feeding of some feedstuffs may be difficult, and the frequency of regurgitation increases with levels of feed intake above 40 g or above one-half
d e p a r t m e n t of Animal Science, 322 Mumford Hall, 1301 West Gregory Drive, University of Illinois, Urbana, IL 61801. 2 To whom correspondence should be addressed.
n o r m a l intake (Sibbald, 1977). Farrell ( 1 9 7 8 ) developed a rapid voluntary intake procedure for determination of apparent metabolizable energy (AME) values. In this assay, crossbred cockerels were trained to consume their normal daily pelleted feed allowance within 1 hr, and the test materials were mixed with an equal portion of basal diet. Thus, force-feeding was eliminated, and higher levels of feed intake were obtained. Chami et al. (1980) evaluated this procedure with White Leghorn roosters fed coarsely ground test materials alone and found that an excreta collection period of more than 24 hr was needed for complete intestinal clearance of dietary residues from several feedstuffs. Recent studies have indicated that correcting excreta energy to nitrogen equilibrium may substantially affect TME values of some feedstuffs (Shires et al., 1980; Parsons et al, 1982; Sibbald and Morse, 1983). Parsons et al. (1982) concluded that true metabolizable energy values corrected to nitrogen equilibrium (TME n ) were lower than TME values due to larger
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ABSTRACT A rapid voluntary feed intake bioassay for the determination of metabolizable energy with Single Comb White Leghorn roosters was evaluated. Roosters were trained to maintain their normal daily feed consumption within a 4-hr period. In Experiment 1, a 24-hr preexperimental fasting period was found to be sufficient for intestinal clearance of dietary residues from the roosters on this feeding regimen. The metabolizable energy (ME) and true metabolizable energy (TME) contents of ground yellow corn, dehulled soybean meal, menhaden fish meal, and corn fermentation solubles were determined by feeding roosters these ingredients alone for 6-hr in Experiments 2 through 5. Excreta were quantitatively collected at 30 and 54 hr after initiation of the feeding period. This method was also used in Experiment 6 to evaluate dehydrated alfalfa meal except that this ingredient was mixed with a stock layer ration to attain adequate intake. During the 30 to 54-hr collection period, energy output (kcal/hr) by roosters fed all ingredients used in Experiment 2 to 5 was greater than that of fasted roosters. Length of excreta collection had less effect on ME values corrected to nitrogen equilibrium than on uncorrected ME values. A reduction in determined true dry matter digestibility and TME values of all ingredients resulted when these values were corrected to nitrogen equilibrium (TME n ). The TME and TME n values (kcal/g of dry matter) for the 54-hr collection period were 3.834 ± .018 and 3.683 ± .014 for ground yellow corn, 3.027 ± .037 and 2.804 ± .029 for dehulled soybean meal, 3.413 + .035 and 2.993 ± .020 for menhaden fish meal, 2.752 ± .074 and 2.650 ± .066 for corn fermentation solubles, and 1.762 ± .143 and 1.710 ± .120 for dehydrated alfalfa meal, respectively. The results of this study indicated that both dry matter digestibility and TME values should be corrected to nitrogen equilibrium to obtain accurate and reproducible values with this type of bioassay. (Key words: true metabolizable energy, feedstuff evaluations)
VOLUNTARY INTAKE BIOASSAY
MATERIALS AND METHODS
In all experiments, Single Comb White Leghorn roosters were housed in individual wire cages and received 14 hr of light per day from 0600 to 2000 hr. The roosters were trained to consume their normal daily feed intake within a 4-hr period. Feeding periods of less than 4 hr did not result in normal daily feed consumption by all roosters. Experiment 1 was conducted to determine if a 24-hr preexperimental fasting period was sufficient for complete intestinal clearance of dietary residues from roosters that had previously consumed a large quantity of feed within a 4-hr period. Fifteen roosters were allowed to consume a stock layer ration (SLR) (Parsons et al., 1982) for 4 hr. Excreta were collected quantitatively from each rooster during the periods 18 to 24, 24 to 30, 30 to 42, and 42 to 48 hr after feed withdrawal and dried to constant weight at 65 C. Five experiments were conducted to evaluate the voluntary intake procedure for determination of dry matter digestibility and metabolizable energy of ground yellow corn (GYC), dehulled soybean meal (DSM), menhaden fish meal (MFM), corn fermentation solubles (CFS), and dehydrated alfalfa meal (DAM), respectively. These feedstuffs were chosen to compare effects of correcting excreta energy to nitrogen equilibrium among ingredients varying considerably in protein content. In Experiments 2 to 5, the first four
feedstuffs were fed as the sole dietary component to 16 or more roosters in each experiment. In Experiment 6, DAM was fed to 10 roosters as part of a dietary mixture consisting of 50% DAM and 50% SLR; the roosters would not consume the DAM alone. The SLR was fed to an additional 10 roosters in the same experiment and the dry matter digestibility and ME of DAM were calculated by difference. Five roosters were fasted throughout each experiment for measurements of metabolic and endogenous energy excretion. In Experiments 2 to 6, the roosters were fasted for 24 hr and then allowed to consume the test diets for 6 hr. The feeding period was extended to 6 hr to compensate partially for an expected reduction in intake of the test ingredients as reported by Schang and Hamilton (1982). Excreta were collected quantitatively from each rooster at 30 and 54 hr after the initiation of the 6-hr feeding period. Feed samples and excreta samples from the 0 to 30-hr and 30 to 54-hr collection periods were dried to constant weight at 65 C and ground to pass through a 60-mesh screen. Gross energy contents of the diets and excreta were determined with an adiabatic bomb calorimeter and nitrogen contents by the Kjeldahl method. Dry matter contents of excreta were determined by redrying subsamples at 65 C for 24 hr to correct for moisture uptake during grinding. This correction averaged about 3% of sample weight. The procedure of Sibbald (1976) was used to calculate the TME values of feedstuffs, and ME values were calculated by the same method, except no corrections for endogenous energy excretion were made. The nitrogen corrections for excreta dry matter and energy were calculated by the method of Parsons et al. (1982). The procedure described by Kessler and Thomas (1981) was used to compute energy output (kcal/hr) during excreta collection periods. Statistical analyses included calculation of means with standard errors and linear regression analyses. Student's t test was used to compare treatment means. RESULTS Average feed intake of the roosters during the 4-hr feeding period was 98 g in Experiment 1. The roosters excreted significantly more dry matter in the 18 to 24-hr ex.reta collection period than in the collection periods after 24 hr postfeeding (Fig. 1). No significant differences
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nitrogen losses from nondietary sources by fasted birds than by fed birds. The effects of nitrogen correction on metabolizable energy (ME) and TME values obtained with rapid voluntary intake procedures such as those of Farrell (1978) and Chami et al. (1980) have not been evaluated. Schang and Hamilton (1982) reported that White Leghorn roosters did not maintain normal feed intake within a daily 1-hr period even after 14 days of training as outlined by Farrell (1978). Preliminary work in our laboratory supported their observations. Therefore, the present study was conducted to evaluate a procedure similar to those of Farrell (1978) and Chami et al. (1980) but using White Leghorn roosters trained to maintain their normal daily feed intake within 4 hr. The effects of length of excreta collection period and correction of excreta energy to nitrogen equilibrium on determined TME values were also investigated.
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18-24 24-30 30-42 42-48 COLLECTION PERIOD (hr)
FIG. 1. Dry matter excreted by 15 roosters from 18 to 48 hr after feed withdrawal; means with standard errors in Experiment 1 (lights were off from 31 to 41 hr).
were observed among the individual collection periods from 24 to 48 hr. The roosters fed GYC, DSM, or SLR consumed, on the average, more than 70 g of feed during the 6-hr feeding period (Table 1). Feed intake for MFM, CFS, and the DAM plus SLR diet were substantially lower than those for the previous feedstuffs. Only 14 of the 18 roosters fed MFM consumed enough feed (more than 15 g) for acceptable digestibility measurements. Apparent digestibility values for the dry matter content of the feedstuffs were lower for the 54-hr collection period than for the 30-hr collection period (Table 1). The nitrogencorrected apparent digestibility values were generally lower than corresponding uncorrected values for the 30-hr collection, but the reverse was true for the 54-hr collection period. Length of excreta collection had no effect on uncorrected true digestibility values for GYC, DSM, SLR, and DAM plus SLR, but these values for MFM and CFS were significantly lower (P<.05) for the 54-hr collection period. Nitrogencorrected true digestibility values were significantly lower (P<.05) than corresponding uncorrected values. Linear regression analysis
DISCUSSION
Farrell (1978) reported that a 70-g level of feed intake should be obtained to ensure that endogenous energy excretion does not influence ME values. Average feed intakes of 70 g or greater were obtained for GYC, DSM, and SLR in our study, but average intakes of MFM and
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indicated that many of the uncorrected true digestibility values were negatively and significantly correlated with feed intake (see footnote, Table 1). However, this relationship was not as pronounced for nitrogen-corrected true digestibility values. Energy output and nitrogen retention values for the two collection periods for Experiments 2 to 6 are presented in Table 2. During the 30 to 54-hr period, the energy output by roosters fed GYC, DSM, MFM, or CFS was significantly greater (P<.05) than endogenous energy excreted by fasted birds. No significant differences in energy outputs between fed and fasted birds were observed in the last experiment. The fasted roosters in the experiments with GYC, DSM, MFM, CFS, and DAM excreted 2.23, 2.16, 1.40, 1.67 and 1.36 g of nitrogen, respectively, during the 54-hr collection period. All roosters fed all test ingredients, except CFS, were in positive nitrogen balance for the 30-hr collection period. However, roosters fed GYC, DSM, CFS, or DAM plus SLR were in negative nitrogen balance for the longer 54-hr collection period, while those fed MFM and SLR remained in positive nitrogen balance. As expected, ME values for the 54-hr collection period were lower than those for the 30-hr period (Table 3). The TME values were also slightly lower for the extended collection period with the difference being significant (P<.05) for GYC (Table 3). The TME n values were lower than the corresponding uncorrected values for both collection periods. Differences due to length of excreta collection were less for ME n than for ME values. The effects of the nitrogen corrections on TME values were greater for MFM and DSM than for the other ingredients. Also, the TME n values for the 54-hr collection period were consistently lower than those for the 30-hr period. The nitrogen excretion accounted for 71.9, 63.5, 54.3, 51.4, and 53.6% of the energy excreted by fasted roosters during the 54-hr period in the experiments with GYC, DSM, MFM, CFS, and DAM, respectively.
VOLUNTARY INTAKE BIOASSAY
E E
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CFS were only 45 g or less. Moreover, average intake of a 50:50 mixture of SLR and DAM was only 52 g, indicating that a 70-g feed consumption may not be obtained for some feedstuffs even when mixed with an equal amount of basal diet. The ME values of all feedstuffs were substantially lower for a 54-hr than for a 30-hr excreta collection period. Increasing the length of excreta collection had a larger effect on ME than TME values, indicating that the decrease in ME values was primarily due to endogenous energy excretion. Results were similar for dry matter digestibility. Thus, this bioassay does not produce accurate ME or dry matter digestibility values if long excreta collection periods are used. The differences due to length of excreta collection were much less for ME n values, indicating the importance of the nitrogen correction for accuracy. For accurate determination of ME n with this bioassay, an excreta collection period of sufficient, but also minimal, duration is needed to reduce the influence of endogenous energy excretion. Farrell (1980) suggests an excreta collection period of 32 hr postfeeding for these types of bioassays. Higher excreta energy output (kcal/hr) by roosters fed GYC, DSM, MFM, and CFS as compared to the fasted controls during the 30 to 54-hr period suggested that a collection period of more than 30 hr was needed for this bioassay. Part of these differences may have been due to influence of the nitrogen content of the test diets on metabolic plus endogenous energy excretion (Shires et al, 1979). However, the consistently lower TME n values (significant for GYC) for the extended collection period indicated that these differences were not entirely related to nitrogen intake and suggested that more than 30 hr were required for complete intestinal clearance of dietary residues. Excreta collection periods of more than 24 hr were reported necessary for DSM (Kessler and Thomas, 1981; Chami et al, 1980) and fish meal (Sibbald, 1979), whereas a 24-hr collection period was sufficient for GYC in these studies. In the present study, the decrease in TME n of GYC for the extended collection period was probably due to the very high level of feed intake for this ingredient. The effect of correcting excreta energy to nitrogen equilibrium on ME and TME values were similar to those observed by Parsons et al. (1982). The nitrogen correction significantly reduced the TME values of GYC, DSM, MFM,
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Dry matter and protein contents (as-fed basis), respectively, of the feed ingredient expressed as percentages were for dehulled soybean meal, 91.8 and 58.6 for menhaden fish meal, 88.7 and 22.3 for corn fermentation solubles, 91 16.9 for dehydrated alfalfa meal.
1
Ground yellow corn Dehulled soybean meal Menhaden fish meal Corn fermentation solubles Stock layer ration (SLR) Dehydrated alfalfa meal plus SLR 5
Observations per mean
Experiment number and feedstuffs1
TABLE 2. Effects of duration of excreta collection period on energy excretion and n
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VOLUNTARY INTAKE BIOASSAY
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and the SLR. This effect occurred primarily because the nitrogen correction accounted for approximately 60% of the average excreta energy of fasted birds. This observation confirms the conclusion of Parsons et al. (1982) that energy excretion of fasted birds overestimates endogenous energy excreted by fed birds. The reductions in TME values due to nitrogen correction ranged from 3.7% for CFS to 12.3% for MFM, with the effect being greater for DSM and MFM than for other ingredients. Sibbald and Morse (1983), using the standard TME bioassay, also found that the nitrogen correction decreased TME values of DSM and fish meal (approximately 10% for 30-g intake) more than those for wheat, oats, or wheat middlings. The variation in magnitude of nitrogen correction among feed ingredients in our study resulted from differences both in nitrogen balance and in nitrogen and feed intakes. The effect of the nitrogen correction is usually greater for high protein feedstuffs due to higher nitrogen retention and because less body protein degradation is needed for maintenance (Shires et al., 1980). However, the amino acid balance and available carbohydrate and fat content of the test ingredient could also influence the sparing effect on body protein. For example, the nitrogen correction had only a small effect on the TME of CFS in our study, because the fed roosters were in large negative nitrogen balance. This large negative nitrogen balance probably resulted from low intake of protein coupled with low intake of fat and available carbohydrate. The nitrogen correction had little effect on TME values for GYC and SLR due to the high intakes of these ingredients. Because the nitrogen correction reduces the endogenous energy correction, the difference between TME and TME n will be greater at lower levels of feed intake. The procedure described herein works well for determination of metabolizable energy of feedstuffs. Feed intakes of 40 to 110 g, which greatly exceeds the 30 g recommended for force-feeding, can be obtained voluntarily. Both ME and TME values should be corrected to nitrogen equilibrium when using this procedure.
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ACKNOWLEDGMENTS
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This study was supported by a grant from the John Lee Pratt Animal Nutrition Program at Virginia Polytechnic Institute and State University, Blacksburg, Virginia. The authors
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wish to express their appreciation to Daniel Grunloh, University of Illinois, for his assistance with chemical analyses. REFERENCES
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Chami, D. B., P. Vohra, and F. H. Kratzer, 1980. Evaluation of a method for determination of true metabolizable energy of feed ingredients. Poultry Sci. 59:569-571. Farrell, D. J., 1978. Rapid determination of metabolizable energy of foods using cockerels. Br. Poult. Sci. 19:303-308. Farrell, D. J., 1980. The "rapid method" of measuring the metabolizable energy of feedstuffs. Feedstuffs 52(45):24, 26. Kessler, J. W., and O. P. Thomas, 1981. The effect of cecectomy and extension of the collection period on the true metabolizable energy values of soybean meal, feather meal, fish meal, and blood meal. Poultry Sci. 60:2639-2647. Parsons, C. M., L. M. Potter, and B. A. Bliss, 1982. True metabolizable energy corrected to nitrogen equilibrium. Poultry Sci. 61:2241-2246.
Schang, M. J., and R.M.G. Hamilton, 1982. Comparison of two direct bioassays using adult cocks and four indirect methods for estimating the metabolizable energy content of different feedingstuffs. Poultry Sci. 61:1344-1353. Shires, A., A. R. Robblee, R. T. Hardin, and D. R. Clandinin, 1979. Effect of previous diet, body weight, and duration of starvation of the assay bird on the true metabolizable energy value of corn. Poultry Sci. 58:602-608. 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. Sibbald, 1. R., 1976. A bioassay for true metabolizable energy in feedingstuffs. Poultry Sci. 55:303—308. Sibbald, I. R., 1977. The effect of level of feed input on true metabolizable energy values. Poultry Sci. 56:1662-1663. Sibbald, I. R., 1979. Passage of feed through the adult rooster. Poultry Sci. 58:446-459. Sibbald, I. R., and P. M. Morse, 1983. Effects of nitrogen correction and of feed intake on true metabolizable energy values. Poultry Sci. 62: 138-142.
1984 Poultry Science 63:1610-1616 INTRODUCTION Sibbald (1976) described a rapid and simple method for the determination of true metabolizable energy (TME) of feedstuffs for poultry. Test ingredients are force-fed as the sole dietary component, and excreta are collected quantitatively for 48 hr (Sibbald, 1979). The TME values are calculated by correcting energy excreted for that which is of metabolic and endogenous origin. Metabolic and endogenous energy is measured by energy excretion of separate fasted birds during the trial. Although rapid, the procedure of Sibbald (1976) has some disadvantages. Force-feeding of some feedstuffs may be difficult, and the frequency of regurgitation increases with levels of feed intake above 40 g or above one-half
d e p a r t m e n t of Animal Science, 322 Mumford Hall, 1301 West Gregory Drive, University of Illinois, Urbana, IL 61801. 2 To whom correspondence should be addressed.
n o r m a l intake (Sibbald, 1977). Farrell ( 1 9 7 8 ) developed a rapid voluntary intake procedure for determination of apparent metabolizable energy (AME) values. In this assay, crossbred cockerels were trained to consume their normal daily pelleted feed allowance within 1 hr, and the test materials were mixed with an equal portion of basal diet. Thus, force-feeding was eliminated, and higher levels of feed intake were obtained. Chami et al. (1980) evaluated this procedure with White Leghorn roosters fed coarsely ground test materials alone and found that an excreta collection period of more than 24 hr was needed for complete intestinal clearance of dietary residues from several feedstuffs. Recent studies have indicated that correcting excreta energy to nitrogen equilibrium may substantially affect TME values of some feedstuffs (Shires et al., 1980; Parsons et al, 1982; Sibbald and Morse, 1983). Parsons et al. (1982) concluded that true metabolizable energy values corrected to nitrogen equilibrium (TME n ) were lower than TME values due to larger
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ABSTRACT A rapid voluntary feed intake bioassay for the determination of metabolizable energy with Single Comb White Leghorn roosters was evaluated. Roosters were trained to maintain their normal daily feed consumption within a 4-hr period. In Experiment 1, a 24-hr preexperimental fasting period was found to be sufficient for intestinal clearance of dietary residues from the roosters on this feeding regimen. The metabolizable energy (ME) and true metabolizable energy (TME) contents of ground yellow corn, dehulled soybean meal, menhaden fish meal, and corn fermentation solubles were determined by feeding roosters these ingredients alone for 6-hr in Experiments 2 through 5. Excreta were quantitatively collected at 30 and 54 hr after initiation of the feeding period. This method was also used in Experiment 6 to evaluate dehydrated alfalfa meal except that this ingredient was mixed with a stock layer ration to attain adequate intake. During the 30 to 54-hr collection period, energy output (kcal/hr) by roosters fed all ingredients used in Experiment 2 to 5 was greater than that of fasted roosters. Length of excreta collection had less effect on ME values corrected to nitrogen equilibrium than on uncorrected ME values. A reduction in determined true dry matter digestibility and TME values of all ingredients resulted when these values were corrected to nitrogen equilibrium (TME n ). The TME and TME n values (kcal/g of dry matter) for the 54-hr collection period were 3.834 ± .018 and 3.683 ± .014 for ground yellow corn, 3.027 ± .037 and 2.804 ± .029 for dehulled soybean meal, 3.413 + .035 and 2.993 ± .020 for menhaden fish meal, 2.752 ± .074 and 2.650 ± .066 for corn fermentation solubles, and 1.762 ± .143 and 1.710 ± .120 for dehydrated alfalfa meal, respectively. The results of this study indicated that both dry matter digestibility and TME values should be corrected to nitrogen equilibrium to obtain accurate and reproducible values with this type of bioassay. (Key words: true metabolizable energy, feedstuff evaluations)
VOLUNTARY INTAKE BIOASSAY
MATERIALS AND METHODS
In all experiments, Single Comb White Leghorn roosters were housed in individual wire cages and received 14 hr of light per day from 0600 to 2000 hr. The roosters were trained to consume their normal daily feed intake within a 4-hr period. Feeding periods of less than 4 hr did not result in normal daily feed consumption by all roosters. Experiment 1 was conducted to determine if a 24-hr preexperimental fasting period was sufficient for complete intestinal clearance of dietary residues from roosters that had previously consumed a large quantity of feed within a 4-hr period. Fifteen roosters were allowed to consume a stock layer ration (SLR) (Parsons et al., 1982) for 4 hr. Excreta were collected quantitatively from each rooster during the periods 18 to 24, 24 to 30, 30 to 42, and 42 to 48 hr after feed withdrawal and dried to constant weight at 65 C. Five experiments were conducted to evaluate the voluntary intake procedure for determination of dry matter digestibility and metabolizable energy of ground yellow corn (GYC), dehulled soybean meal (DSM), menhaden fish meal (MFM), corn fermentation solubles (CFS), and dehydrated alfalfa meal (DAM), respectively. These feedstuffs were chosen to compare effects of correcting excreta energy to nitrogen equilibrium among ingredients varying considerably in protein content. In Experiments 2 to 5, the first four
feedstuffs were fed as the sole dietary component to 16 or more roosters in each experiment. In Experiment 6, DAM was fed to 10 roosters as part of a dietary mixture consisting of 50% DAM and 50% SLR; the roosters would not consume the DAM alone. The SLR was fed to an additional 10 roosters in the same experiment and the dry matter digestibility and ME of DAM were calculated by difference. Five roosters were fasted throughout each experiment for measurements of metabolic and endogenous energy excretion. In Experiments 2 to 6, the roosters were fasted for 24 hr and then allowed to consume the test diets for 6 hr. The feeding period was extended to 6 hr to compensate partially for an expected reduction in intake of the test ingredients as reported by Schang and Hamilton (1982). Excreta were collected quantitatively from each rooster at 30 and 54 hr after the initiation of the 6-hr feeding period. Feed samples and excreta samples from the 0 to 30-hr and 30 to 54-hr collection periods were dried to constant weight at 65 C and ground to pass through a 60-mesh screen. Gross energy contents of the diets and excreta were determined with an adiabatic bomb calorimeter and nitrogen contents by the Kjeldahl method. Dry matter contents of excreta were determined by redrying subsamples at 65 C for 24 hr to correct for moisture uptake during grinding. This correction averaged about 3% of sample weight. The procedure of Sibbald (1976) was used to calculate the TME values of feedstuffs, and ME values were calculated by the same method, except no corrections for endogenous energy excretion were made. The nitrogen corrections for excreta dry matter and energy were calculated by the method of Parsons et al. (1982). The procedure described by Kessler and Thomas (1981) was used to compute energy output (kcal/hr) during excreta collection periods. Statistical analyses included calculation of means with standard errors and linear regression analyses. Student's t test was used to compare treatment means. RESULTS Average feed intake of the roosters during the 4-hr feeding period was 98 g in Experiment 1. The roosters excreted significantly more dry matter in the 18 to 24-hr ex.reta collection period than in the collection periods after 24 hr postfeeding (Fig. 1). No significant differences
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nitrogen losses from nondietary sources by fasted birds than by fed birds. The effects of nitrogen correction on metabolizable energy (ME) and TME values obtained with rapid voluntary intake procedures such as those of Farrell (1978) and Chami et al. (1980) have not been evaluated. Schang and Hamilton (1982) reported that White Leghorn roosters did not maintain normal feed intake within a daily 1-hr period even after 14 days of training as outlined by Farrell (1978). Preliminary work in our laboratory supported their observations. Therefore, the present study was conducted to evaluate a procedure similar to those of Farrell (1978) and Chami et al. (1980) but using White Leghorn roosters trained to maintain their normal daily feed intake within 4 hr. The effects of length of excreta collection period and correction of excreta energy to nitrogen equilibrium on determined TME values were also investigated.
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14 r' .1 -
ol
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1
1
18-24 24-30 30-42 42-48 COLLECTION PERIOD (hr)
FIG. 1. Dry matter excreted by 15 roosters from 18 to 48 hr after feed withdrawal; means with standard errors in Experiment 1 (lights were off from 31 to 41 hr).
were observed among the individual collection periods from 24 to 48 hr. The roosters fed GYC, DSM, or SLR consumed, on the average, more than 70 g of feed during the 6-hr feeding period (Table 1). Feed intake for MFM, CFS, and the DAM plus SLR diet were substantially lower than those for the previous feedstuffs. Only 14 of the 18 roosters fed MFM consumed enough feed (more than 15 g) for acceptable digestibility measurements. Apparent digestibility values for the dry matter content of the feedstuffs were lower for the 54-hr collection period than for the 30-hr collection period (Table 1). The nitrogencorrected apparent digestibility values were generally lower than corresponding uncorrected values for the 30-hr collection, but the reverse was true for the 54-hr collection period. Length of excreta collection had no effect on uncorrected true digestibility values for GYC, DSM, SLR, and DAM plus SLR, but these values for MFM and CFS were significantly lower (P<.05) for the 54-hr collection period. Nitrogencorrected true digestibility values were significantly lower (P<.05) than corresponding uncorrected values. Linear regression analysis
DISCUSSION
Farrell (1978) reported that a 70-g level of feed intake should be obtained to ensure that endogenous energy excretion does not influence ME values. Average feed intakes of 70 g or greater were obtained for GYC, DSM, and SLR in our study, but average intakes of MFM and
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indicated that many of the uncorrected true digestibility values were negatively and significantly correlated with feed intake (see footnote, Table 1). However, this relationship was not as pronounced for nitrogen-corrected true digestibility values. Energy output and nitrogen retention values for the two collection periods for Experiments 2 to 6 are presented in Table 2. During the 30 to 54-hr period, the energy output by roosters fed GYC, DSM, MFM, or CFS was significantly greater (P<.05) than endogenous energy excreted by fasted birds. No significant differences in energy outputs between fed and fasted birds were observed in the last experiment. The fasted roosters in the experiments with GYC, DSM, MFM, CFS, and DAM excreted 2.23, 2.16, 1.40, 1.67 and 1.36 g of nitrogen, respectively, during the 54-hr collection period. All roosters fed all test ingredients, except CFS, were in positive nitrogen balance for the 30-hr collection period. However, roosters fed GYC, DSM, CFS, or DAM plus SLR were in negative nitrogen balance for the longer 54-hr collection period, while those fed MFM and SLR remained in positive nitrogen balance. As expected, ME values for the 54-hr collection period were lower than those for the 30-hr period (Table 3). The TME values were also slightly lower for the extended collection period with the difference being significant (P<.05) for GYC (Table 3). The TME n values were lower than the corresponding uncorrected values for both collection periods. Differences due to length of excreta collection were less for ME n than for ME values. The effects of the nitrogen corrections on TME values were greater for MFM and DSM than for the other ingredients. Also, the TME n values for the 54-hr collection period were consistently lower than those for the 30-hr period. The nitrogen excretion accounted for 71.9, 63.5, 54.3, 51.4, and 53.6% of the energy excreted by fasted roosters during the 54-hr period in the experiments with GYC, DSM, MFM, CFS, and DAM, respectively.
VOLUNTARY INTAKE BIOASSAY
E E
E E
CFS were only 45 g or less. Moreover, average intake of a 50:50 mixture of SLR and DAM was only 52 g, indicating that a 70-g feed consumption may not be obtained for some feedstuffs even when mixed with an equal amount of basal diet. The ME values of all feedstuffs were substantially lower for a 54-hr than for a 30-hr excreta collection period. Increasing the length of excreta collection had a larger effect on ME than TME values, indicating that the decrease in ME values was primarily due to endogenous energy excretion. Results were similar for dry matter digestibility. Thus, this bioassay does not produce accurate ME or dry matter digestibility values if long excreta collection periods are used. The differences due to length of excreta collection were much less for ME n values, indicating the importance of the nitrogen correction for accuracy. For accurate determination of ME n with this bioassay, an excreta collection period of sufficient, but also minimal, duration is needed to reduce the influence of endogenous energy excretion. Farrell (1980) suggests an excreta collection period of 32 hr postfeeding for these types of bioassays. Higher excreta energy output (kcal/hr) by roosters fed GYC, DSM, MFM, and CFS as compared to the fasted controls during the 30 to 54-hr period suggested that a collection period of more than 30 hr was needed for this bioassay. Part of these differences may have been due to influence of the nitrogen content of the test diets on metabolic plus endogenous energy excretion (Shires et al, 1979). However, the consistently lower TME n values (significant for GYC) for the extended collection period indicated that these differences were not entirely related to nitrogen intake and suggested that more than 30 hr were required for complete intestinal clearance of dietary residues. Excreta collection periods of more than 24 hr were reported necessary for DSM (Kessler and Thomas, 1981; Chami et al, 1980) and fish meal (Sibbald, 1979), whereas a 24-hr collection period was sufficient for GYC in these studies. In the present study, the decrease in TME n of GYC for the extended collection period was probably due to the very high level of feed intake for this ingredient. The effect of correcting excreta energy to nitrogen equilibrium on ME and TME values were similar to those observed by Parsons et al. (1982). The nitrogen correction significantly reduced the TME values of GYC, DSM, MFM,
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2.07 4.26 1.93 3.38 2.79 3.57 ± ± ± ± + +
0-30 3
.11' .23 .17 .28 .11 .42
.70 .81 .54 .69 .41 .51
± ± ± ± ± ±
.04 .04 .04 .04 .02 .04
(kcal/hr) -
30-54
Energy output
.49 .52 .39 .52 .50 .50
± .03 ± .07 ± .04 ± .05 ± .04 ± .04
0-54
Endogeno energy 2 o
Length of excreta collection period in hours.
Fasted roosters.
5
Diet contained 50% dehydrated alfalfa meal and 50% SLR on a dry matter basis.
' Means ± standard errors.
!
2
Dry matter and protein contents (as-fed basis), respectively, of the feed ingredient expressed as percentages were for dehulled soybean meal, 91.8 and 58.6 for menhaden fish meal, 88.7 and 22.3 for corn fermentation solubles, 91 16.9 for dehydrated alfalfa meal.
1
Ground yellow corn Dehulled soybean meal Menhaden fish meal Corn fermentation solubles Stock layer ration (SLR) Dehydrated alfalfa meal plus SLR 5
Observations per mean
Experiment number and feedstuffs1
TABLE 2. Effects of duration of excreta collection period on energy excretion and n
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VOLUNTARY INTAKE BIOASSAY
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and the SLR. This effect occurred primarily because the nitrogen correction accounted for approximately 60% of the average excreta energy of fasted birds. This observation confirms the conclusion of Parsons et al. (1982) that energy excretion of fasted birds overestimates endogenous energy excreted by fed birds. The reductions in TME values due to nitrogen correction ranged from 3.7% for CFS to 12.3% for MFM, with the effect being greater for DSM and MFM than for other ingredients. Sibbald and Morse (1983), using the standard TME bioassay, also found that the nitrogen correction decreased TME values of DSM and fish meal (approximately 10% for 30-g intake) more than those for wheat, oats, or wheat middlings. The variation in magnitude of nitrogen correction among feed ingredients in our study resulted from differences both in nitrogen balance and in nitrogen and feed intakes. The effect of the nitrogen correction is usually greater for high protein feedstuffs due to higher nitrogen retention and because less body protein degradation is needed for maintenance (Shires et al., 1980). However, the amino acid balance and available carbohydrate and fat content of the test ingredient could also influence the sparing effect on body protein. For example, the nitrogen correction had only a small effect on the TME of CFS in our study, because the fed roosters were in large negative nitrogen balance. This large negative nitrogen balance probably resulted from low intake of protein coupled with low intake of fat and available carbohydrate. The nitrogen correction had little effect on TME values for GYC and SLR due to the high intakes of these ingredients. Because the nitrogen correction reduces the endogenous energy correction, the difference between TME and TME n will be greater at lower levels of feed intake. The procedure described herein works well for determination of metabolizable energy of feedstuffs. Feed intakes of 40 to 110 g, which greatly exceeds the 30 g recommended for force-feeding, can be obtained voluntarily. Both ME and TME values should be corrected to nitrogen equilibrium when using this procedure.
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ACKNOWLEDGMENTS
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This study was supported by a grant from the John Lee Pratt Animal Nutrition Program at Virginia Polytechnic Institute and State University, Blacksburg, Virginia. The authors
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1615
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PARSONS ET AL.
wish to express their appreciation to Daniel Grunloh, University of Illinois, for his assistance with chemical analyses. REFERENCES
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Chami, D. B., P. Vohra, and F. H. Kratzer, 1980. Evaluation of a method for determination of true metabolizable energy of feed ingredients. Poultry Sci. 59:569-571. Farrell, D. J., 1978. Rapid determination of metabolizable energy of foods using cockerels. Br. Poult. Sci. 19:303-308. Farrell, D. J., 1980. The "rapid method" of measuring the metabolizable energy of feedstuffs. Feedstuffs 52(45):24, 26. Kessler, J. W., and O. P. Thomas, 1981. The effect of cecectomy and extension of the collection period on the true metabolizable energy values of soybean meal, feather meal, fish meal, and blood meal. Poultry Sci. 60:2639-2647. Parsons, C. M., L. M. Potter, and B. A. Bliss, 1982. True metabolizable energy corrected to nitrogen equilibrium. Poultry Sci. 61:2241-2246.
Schang, M. J., and R.M.G. Hamilton, 1982. Comparison of two direct bioassays using adult cocks and four indirect methods for estimating the metabolizable energy content of different feedingstuffs. Poultry Sci. 61:1344-1353. Shires, A., A. R. Robblee, R. T. Hardin, and D. R. Clandinin, 1979. Effect of previous diet, body weight, and duration of starvation of the assay bird on the true metabolizable energy value of corn. Poultry Sci. 58:602-608. 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. Sibbald, 1. R., 1976. A bioassay for true metabolizable energy in feedingstuffs. Poultry Sci. 55:303—308. Sibbald, I. R., 1977. The effect of level of feed input on true metabolizable energy values. Poultry Sci. 56:1662-1663. Sibbald, I. R., 1979. Passage of feed through the adult rooster. Poultry Sci. 58:446-459. Sibbald, I. R., and P. M. Morse, 1983. Effects of nitrogen correction and of feed intake on true metabolizable energy values. Poultry Sci. 62: 138-142.