Nutrient Digestibility in Food Waste Ingredients for Pekin and Muscovy Ducks

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1 Nutrient Digestibility in Food Waste Ingredients for Pekin and Muscovy Ducks A. FARHAT, L. NORMAND, E. R. CHAVEZ,1 and S. P. TOUCHBURN Department of Animal Science, Macdonald Campus of McGill University, 21,111 Lakeshore Road, Ste-Anne de Bellevue, Québec, Canada, H9X 3V9 ABSTRACT Food wastes are valuable resources to be recycled into new added-value products through animal production. The determination of energy and digestibility values of these wastes is essential for feed formulation. Corn, soybean meal (SBM), and a total of nine industrial food waste ingredients were tested in a comparative metabolic study in Pekin and Muscovy ducklings at two different ages during growth. The precision-feeding technique was employed to establish DM, fat, and fiber digestibility as well as retention of N and energy (AME, AME n in Pekins; and AME, AME n, TME, TME n in Muscovies) for the 11 ingredients. For Pekin at 3 wk of age, the AME n of peanuts, tofu, pogo, granola, waste diet, bread, corn, SBM, okara, and brewers grains were 5,141, 4,019, 3,971, 3,908, 3,141, 2,279, 1,572, and 1,442 kcal/kg, respectively. For Pekin at 6 wk of age, the AME n of peanuts, pogo, tofu, granola, waste diet, bread, corn, SBM, and okara were 5,340, 4,327, 4,254, 4,079, 3,567, 3,302, 3,201, 2,416, and 1,562 kcal/kg, respectively. For Muscovy at 7 wk of age, the TME n of peanuts, pogo, granola, waste diet, corn, tofu, bread, SBM, okara, and peanut skin were 5,207, 4,321, 4,057, 3,733, 3,233, 3,180, 3,084, 2,236, 1,575, and 904 kcal/kg, respectively. For Muscovy at 11 wk of age, the TME n of peanuts, pogo, granola, tofu, waste diet, corn, bread, SBM, okara, and brewers grains were 5,077, 4,137, 4,025, 3,921, 3,586, 3,254, 3,123, 2,245, 2,007, and 1,392 kcal/kg, respectively. Nitrogen retention was significantly (P < 0.05) higher for SBM, tofu, okara, pogo, peanuts, and the food waste diet and lower for bread, corn, granola, brewers grains, and peanut skin. Dry matter digestibility was high for granola, pogo, corn, bread, and the food waste diet. Fat digestibility was generally the same for all the ingredients and was consistently over 97%. Bread neutral detergent fiber (NDF) was significantly (P < 0.05) the most digestible (88.92% NDF digestibility), as it consisted of 96.29% hemicellulose, whereas okara NDF was significantly (P < 0.05) the least digestible (26.94% NDF digestibility) and contained only 14.38% hemicellulose. Peanut skins and SBM with 30% hemicellulose showed only slightly higher digestibilities of NDF. The results of this study establish reliable data for formulation of duck diets using the tested industrial food waste ingredients as well as corn and SBM in both Pekin and Muscovy ducklings at two different ages during growth to market weight. (Key words: industrial food waste, metabolizable energy, nutrients, digestibility, duck) INTRODUCTION There are many important reasons for the determination of the ME values of ingredients used in formulating diets for poultry. Increase in efficiency of nutrient utilization and a consequent reduction in nutrient excretion to minimize environmental impact require the determination of nutrient and energy utilization values for feed ingredients used in diet formulation. Energy values used to formulate diets for ducks are mainly 1998 Poultry Science 77: adopted from tables of chicken bioassay data. However, evidence on the similarities of N and energy metabolism in ducks and chickens is equivocal. Among others, Siregar and Farrell (1980) and Ostrowski-Meissner (1984) reported differences in the metabolizability of energy and N values obtained for several diets between chickens and ducks of the same age. Studies on the feeding of food wastes to producing animals have been reported (Cozzi and Polan, 1994; El-Bouchy and Van der Poel, 1994; Utley and Hellwig, 1985; Zia-Ur-Rehman et al., 1994), but no data on the energy and digestibility values of the feed ingredients are available. Received for publication November 13, Accepted for publication April 22, To whom correspondence should be addressed: chavez@agradm.lan.mcgill.ca Abbreviation Key: ADF = acid detergent fiber; GE = gross energy; NDF = neutral detergent fiber; SBM = soybean meal. 1371

2 1372 The growth performance and carcass analysis studies we conducted (Farhat et al., 1997) have clearly established the industrial food waste ingredients as valuable resources. Future formulation with food wastes must be based on reliable values of the ME of the food waste ingredients. The objective of this study was to determine AME, AME n, TME, TME n, N retention, DM digestibility, fat digestibility, and neutral detergent fiber (NDF) digestibility of corn, soybean meal (SBM), and nine existing industrial food waste ingredients in Pekin and Muscovy ducklings at two different ages during growth to market weight. MATERIALS AND METHODS Experimental Design and Feeding Program Three hundred Pekin and Muscovy day-old male ducklings were purchased from local commercial hatcheries. The ducklings were housed in floor pens and fed commercial pelleted duck diets during the preexperimental periods. At the age 3 and 6 wk, for Pekin and 7 and 11 wk for Muscovy breeds, 30 birds per breed per age were randomly selected and moved from floor pens to individual metabolic cages with 38, 50, and 50 cm of width, length, and height, respectively. New birds were taken from the floor pens for each age trial. The ages 3 and 7 wk and 6 and 11 wk represented the growing and finishing periods, respectively, of the Pekin and Muscovy breeds. Each bird served as an experimental unit with five birds per waste ingredient to be tested. The reference ingredient, corn, was fed to 10 birds. Once in the cages, they were provided commercial pellets for ad libitum consumption during 2 d of adaptation. All the birds were deprived of feed for 24 h to ensure that their alimentary canals were empty of feed residues (Sibbald, 1979; Carré et al., 1990). This was followed by another 24 h period of feed deprivation, during which the total excreta voided by each bird was collected and frozen. Each bird served as its own negative control to estimate metabolic and endogenous excretion. The birds were maintained under continuous light to avoid delay in voiding excreta such as may occur during periods of darkness (Sibbald and Morse, 1983). A stainless steel funnel with 40 cm stem (external diameter, 1.3 cm, internal diameter, 1.1 cm) was used in the precision-feeding technique. The amounts of test ingredients used were 20, 40, and 60 g for 3-, 6-, and 7-, or 11-wk-old ducklings. To avoid any impaction, this amount was based on the capacity of the ducklings to accommodate feed in the enlargement of the lower esophagus. This capacity was determined by a preliminary assay using the different waste ingredients that were high in fiber and have 2Virtis freeze dryer , Gardiner, NY FARHAT ET AL. relatively lower densities than the others. Once fed, the birds were individually housed in the clean wire-floored metabolic cages over excreta collection trays measuring 45, 55, and 5 cm of width, length, and height, respectively, and their housing times were recorded. Rigid plastic panels approximately 15 cm high were installed to the lower portion of each cage wire mesh fence to minimize cross-contamination of the excreta. This was done after observing excreta cross-contamination with the Pekin ducks during the collection of endogenous excreta. Water was offered, starting 2 h after the feeding, to avoid regurgitation, which was the main reason for eliminating observations. Excreta was collected 24 h after precisionfeeding. The experimental procedure was conducted in accordance with the guidelines specified by the Canadian Council on Animal Care (1984). The total excreta was collected in plastic trays. The diets and excreta samples were frozen, freeze-dried,2 allowed to come to equilibrium with the atmospheric moisture, weighed, and ground through a 0.5-mm sieve. The ground samples were assayed for gross energy (GE) in an adiabatic oxygen bomb calorimeter. Samples were then analyzed for DM, N, acid detergent fiber (ADF), NDF, and total lipids to determine DM digestibility, N retention, fiber, and fat digestibility. The data were used to calculate AME, AME n, TME, and TME n values of the test material. Apparent and true ME are calculated according to the following formulas: AME = IE EE TME = AME + FEL where IE = ingested energy; EE = excreta energy voided by the fed bird; and FEL = fasting energy loss by the unfed bird. The values corrected to zero N balance, AME n and TME n, are calculated as follows: AME n = AME (8.22 ANR/FI) TME n = TME (8.22 FNL/FI) (8.22 ANR/FI) where ANR = apparent N retention calculated as the difference between N intake and N output; FI = feed intake; and FNL = fasting N loss by the unfed bird. The GE excreted was corrected to zero N balance using the factor of 8.22 kcal/g of N retained in the body or voided as products of tissue catabolism (Hill and Anderson, 1958). The selection of industrial food waste ingredients to be tested was based on their availability in large supply, their quality in terms of protein and energy as potential alternatives for conventional feedstuffs, and the least processing needed before being used. It was also based on the preliminary feeding studies (Chavez et al., 1995) using a variety of these ingredients with ducks that pointed to their potential and indicated the usefulness of further nutritional evaluation in order to achieve optimum performance. Thus, 11 test feed ingredients were selected for nutritive value assessment in these comparative metabolic

3 ENERGY AND DIGESTIBILITY VALUES OF FOOD WASTES 1373 TABLE 1. Chemical analysis 1 of the food waste ingredients tested in the metabolic studies (DM basis) Waste Crude Hemi- Gross ingredients DM FAT protein NDF ADF cellulose a Ash energy (%) (kcal/kg) Peanut ,634 Bread ,387 Granola ,811 Corn ,853 Soybean meal ,116 Peanut skins ,864 Waste diet ,370 Pogo ,068 Tofu ,267 Brewers grains ,193 Okara ,468 ahemicellulose as percentage of the neutral detergent fiber. 1Chemical analysis was conducted at the Crampton Nutrition Laboratory, Macdonald Campus of McGill University, Ste-Anne de Bellevue, QC, Canada, H9X 3V9. studies between Pekin and Muscovy ducklings. They included corn and SBM as reference conventional feedstuffs and nine industrial food waste ingredients from the Greater Montreal region. Description of Waste Ingredients Okara is a by-product of soybean processing for tofu (soybean curd) production, commonly called okara fiber because of its high fiber content. Tofu is a curd produced by fermentation of soybeans, discarded mainly for being in a shape unsuitable for marketing. Granola is a candy bar composed of cereals, nuts, sugar, and chocolate, which is discarded because of decoding in its component mixture that cause variations in taste, making it unsuitable for sale. Bread is discarded because it is stale or misshapen. Brewers grains are a by-product of the malting process in the brewing industry. Pogo is a weiner on a stick enveloped in dough and deep fried, discarded because of over- or undercooking, being misshapen, or held beyond the expiration date. Peanut and peanut skins consist of old peanuts and the peanut skins removed during processing. The food waste diet, is a sample of the diet formulated exclusively of food waste, was used for assessment of its nutritive value as it represents the combined form of these waste ingredients. The chemical analyses data of these ingredients are shown in Table 1. Following freeze-drying, the absolute dry matter values were obtained using a vacuum oven.3 The samples were ground through a 0.5-mm screen,4 for the precision-feeding technique, and to powder before being subjected to chemical analysis. Gross energy was measured using an adiabatic oxygen bomb calorimeter.5 Crude protein was measured using a N analyzer.6 The NDF and ADF values were determined using the method 3National Appliance Co., Portland, OR Tecator grinder 3260, cyclotec, 1093 sample mill, Höganäs, Sweden. 5Number 1241, Parr Instrument Co., Moline, IL Leco FP-428, Leco Corp., St. Joseph, MI Model F-A1730, Sybron Thermolyne, Dubuque, IA developed by Goering and Van Soest (1970) and fat was ether extracted. The ash content was determined using a muffle furnace.7 Statistical Analysis Statistical analyses of the data as a completely randomized design were performed using the General Linear Models procedure of the SAS (SAS Institute, 1990) library. The multicomparison Sheffe s test was used to separate the differences between the means for statistical significance (P < 0.05). RESULTS AND DISCUSSION Brewers grains and peanut skins were the only food waste ingredients that provoked regurgitation problems during precision feeding. The physical structure of the fiber in the brewers grains and the tannins in the peanut skins were the likely major causes of esophageal irritations resulting in regurgitation. In subsequent trials, brewers grains and peanut skins were mixed with corn as a diluent at a ratio of 1:2 and 1:3, respectively. Even these proportions induced regurgitation in some ducklings. Pekin ducklings at 3 wk of age (Table 2) were in slight negative N balance when fed granola, bread, corn, and brewers grains, whereas those fed okara, peanut, pogo, SBM, tofu, and the composed food waste diet were in positive N balance. These responses were reasonable because the latter ingredients have higher total energy value and also are rich protein sources. The TME and TME n were not determined in Pekin ducks due to cross-contamination of excreta during the collection of endogenous excreta. The AME and AME n values show that peanut was the best and tofu, pogo, and granola were significantly (P < 0.05) superior to the other ingredients, including corn and SBM, which values were not significantly (P > 0.05) different from those of bread and the composed food waste diet. Dry matter digestibilities of granola and pogo were superior to those of the other ingredients except for corn that was

4 1374 FARHAT ET AL. TABLE 2. Nitrogen retention, AME, AME n, and DM, fat, and neutral detergent fiber (NDF) digestibility values of the tested ingredients for Pekin ducklings at 3 wk of age Ingredient DM Fat NDF N retention AME AME n Peanut c ab b 413 ab 5,311 a 5,141 a Bread c ND a 63 bc 3,117 d 3,142 c Granola a ab ND 39 bc 3,892 c 3,908 b Corn bc b c 72 c 3,111 d 3,141 c Soybean meal e ND d 473 ab 2,474 e 2,279 d Waste diet c c b 172 b 3,257 d 3,186 c Pogo ab a ND 368 ab 4,122 bc 3,971 b Tofu d ab ND 588 a 4,261 b 4,019 b Brewers grains f ND de 301 c 1,271 g 1,442 e Okara d a 9.26 e 400 ab 1,736 f 1,572 e SEM a gmeans within columns with no common superscript differ significantly (P < 0.05). 1Fat and NDF digestibility of some ingredients, that are low in these nutrients, were not determined. The observations for peanut skins were not determined due to regurgitation. inferior (P < 0.05) to granola but not to pogo (Table 2). The percentage digestibility of fat in the ingredients ranged between and 99.48% without acid hydrolysis. The differences in digestibility may be due to differences in the chain length of fatty acids and the proportions of saturated and unsaturated fatty acids. The digestibility of NDF was significantly (P < 0.05) higher for bread followed by peanut, and the food waste diet. The digestibilities of the NDF in corn and SBM were below 50% and in okara and brewers grains were significantly (P < 0.05) lower than in corn. Most of the variability in NDF digestibilities can be explained by the proportion of the hemicellulose component in the NDF of these ingredients (Table 1). For example, NDF (cellulose, hemicellulose, and lignin) in bread is 25.6% and ADF is 0.95% which means that the hemicellulose content of bread NDF is 96.29% and this explains the high NDF digestibility of bread. Okara, however, has TABLE 3. Nitrogen retention, AME, AME n, and DM, fat, and neutral detergent fiber (NDF) digestibility values of the tested ingredients for Pekin ducklings at 6 wk of age 13.70% NDF, 11.73% ADF, and, hence, 14.38% hemicellulose in its NDF, which explains most of its low NDF digestibility. Pekin ducklings maintained a positive N balance at 6 wk of age (Table 3) even when fed the ingredients that are relatively low in protein, although this balance was significantly (P < 0.05) lower than that of the birds fed ingredients high in protein such as tofu, okara, and SBM. Thus, the birds receiving 40 g by precision feeding, as compared to 20 g at 3 wk of age, mobilized less endogenous amino acids to meet their maintenance energy requirement. The AME and AME n values followed the same trend as at 3 wk of age, with peanut having significantly (P < 0.05) the highest value followed by pogo, tofu, and then granola. Also at this age, the Pekin ducklings were able to digest more (P < 0.05) dry matter from granola, pogo, bread, and corn than from the other ingredients. There was no signifi- Ingredient DM Fat NDF N retention AME AME n Peanut c a b 648 cd 5,473 a 5,340 a Bread ab ND a 226 e 3,348 e 3,302 e Granola a a ND 7 e 4,081 c 4,079 c Corn ab a c 137 e 3,229 e 3,201 e Soybean meal d ND d 1,778 a 2,781 f 2,416 f Waste diet bc a c 464 d 3,662 d 3,567 d Pogo a a ND 754 c 4,482 b 4,327 b Tofu c a ND 1,991 a 4,663 b 4,254 bc Okara d a d 1,237 b 1,816 g 1,562 g SEM a gmeans within columns with no common superscript differ significantly (P < 0.05). 1Fat and NDF digestibility of some ingredients, that are low in these nutrients, were not determined. The observations for brewers grains and peanut skins were not determined due to regurgitation.

5 ENERGY AND DIGESTIBILITY VALUES OF FOOD WASTES 1375 TABLE 4. Nitrogen retention, AME, AME n, TME, TME n and DM, fat, and neutral detergent fiber (NDF) digestibility values of the tested ingredients for Muscovy ducklings at 7 wk of age Ingredient DM Fat NDF N retention AME AME n TME TME n Peanut c b b 756 c 5,352 a 5,197 a 5,362 a 5,207 a Bread b ND a 224 d 3,282 d 3,231 e 3,282 e 3,084 d Granola a a ND 102 d 4,070 c 4,050 c 4,078 c 4,057 bc Corn ab a d 185 d 3,313 d 3,275 e 3,318 e 3,233 d Soybean meal cd ND e 1,863 a 2,885 e 2,502 f 2,885 f 2,236 e Peanut skin e a d 279 e 655 g 884 h 674 h 904 g Waste diet ab a c 639 c 3,854 c 3,723 d 3,864 d 3,733 c Pogo ab a ND 859 c 4,486 b 4,310 b 4,497 b 4,321 b Tofu d c ND 1,452 b 3,891 c 3,575 d 3,892 d 3,180 d Okara cd a e 1,205 b 2,030 f 1,775 g 2,030 g 1,575 f SEM a hmeans within columns with no common superscript differ significantly (P < 0.05). 1Fat and NDF digestibility of some ingredients, that are low in these nutrients, were not determined. The observations for brewers grains were not determined due to regurgitation. cant (P > 0.05) difference among ingredients for fat digestibility, with values consistently over 97%. The digestibility of NDF followed the same trend at 6 wk as at 3 wk of age, with bread NDF having the most digestible fraction (P < 0.05). The digestibilities, N retentions, and metabolizable energy values of the ingredients for Pekin ducklings mostly increased from 3 to 6 wk of age. The energy value of the waste diet increased by 11%. Muscovy birds were in positive N balance at both ages except for the birds fed peanut skins (Tables 4 and 5). Tofu, okara, and SBM were significantly (P < 0.05) superior to the other ingredients in terms of N retention. For AME, AME n, TME, and TME n, peanut had significantly (P < 0.05) the highest value, followed by pogo and granola. Due to their higher values of N retention, SBM, tofu, and okara had lower AME n and TME n values than the other ingredients. Dry matter digestibilities of corn, granola, pogo, and the food waste diet were not TABLE 5. Nitrogen retention, AME, AME n, TME, TME n and DM, fat, and neutral detergent fiber (NDF) digestibility values of the tested ingredients for Muscovy ducklings at 11 wk of age significantly (P > 0.05) different. Percentage of NDF digestibility reflects the hemicellulose content of the ingredients, where bread was significantly (P < 0.05) higher in NDF digestibility, followed by peanut and the food waste diet. Okara, which had the lowest level of hemicellulose (14.38%), exhibited the lowest NDF digestibility. The differences in digestibility of DM for Muscovy ducklings between 7 and 11 wk of age were characterized by a decrease for SBM associated with reduced NDF digestibility, an increase for okara, and no difference for the other ingredients. The digestibility of NDF for Muscovies decreased from 7 to 11 wk of age for SBM, increased for corn and okara; and showed no difference for the other ingredients. In general, the mean energy and digestibility values of the tested ingredients show that the energy values for corn and SBM are closely comparable to those reported for ducks in the literature (Mohamed et al., 1984; Ingredient DM Fat NDF N retention AME AME n TME TME n Peanut e b b 1,059 b 5,208 a 5,064 a 5,222 a 5,077 a Bread cd ND a 546 c 3,276 d 3,201 d 3,289 d 3,123 e Granola a ab ND 213 d 4,045 b 4,016 b 4,055 b 4,025 bc Corn ab b c 363 c 3,291 d 3,241 d 3,303 d 3,254 e Soybean meal f ND e 2,345 a 2,553 e 2,231 e 2,566 e 2,245 f Waste diet bc ab c 1,040 b 3,716 c 3,574 c 3,729 c 3,586 d Pogo ab ab ND 1,336 b 4,309 b 4,126 b 4,320 b 4,137 bc Tofu e b ND 2,544 a 4,254 b 3,905 b 4,270 b 3,921 c Brewers grains g ND e 123 d 1,426 f 1,293 f 1,443 f 1,392 g Okara de ab d 2,298 a 2,320 e 1,995 e 2,332 e 2,007 f SEM a gmeans within columns with no common superscript differ significantly (P < 0.05). 1Fat and NDF digestibility of some ingredients, that are low in these nutrients, were not determined. The observations for peanut skins were not determined due to regurgitation.

6 1376 Ostrowski-Meissner, 1984). Ragland et al. (1997) reported AME n for corn of and kcal/g in two experiments with Pekin ducks, which agree very closely with our values of and kcal/g. The industrial food waste energy values fluctuated higher and lower than corn and SBM with the composed waste diet values reasonably comparable to these conventional feedstuffs commonly used in poultry diets. These results are promising and should encourage further research toward establishing tables of energy and digestibility values for alternative feedstuffs as an incentive for their utilization in feed formulation. As the data presented reveal, these ingredients exhibit at least similar nutritive values to those of conventional feedstuffs. The interrelationships between the age of the ducklings and their metabolic activities suggest that different values must be retained in ration formulation for certain feedstuffs according to growth periods of the ducks. Overall the Muscovies at 7 and 11 wk of age and the Pekins at 6 wk of age exhibit generally similar values for digestibility and AME n, whereas these tend to be lower for the Pekins at 3 wk of age. This result suggests that the Pekin at 3 wk of age is less mature than the Muscovy at 7 wk of age. Some of these results point out the importance of differentiating NDF and ADF digestibilities in order to explain the ability of ducks to digest fiber. As industrial food wastes have been proven to be valuable and capable of replacing conventional feedstuffs in duck diets, it is no longer appropriate to qualify them as wastes, but rather as by-products or nonconventional feedstuffs. Hence, the determination of their real nutritive values will ensure better utilization of these feedstuffs and help to formulate balanced diets in terms of energy to protein ratio to maintain or improve carcass quality. REFERENCES Canadian Council on Animal Care, Guide to the Care and Use of Experimental Animals. Vol. 2. Ottawa, ON, Canada. Carré, B., L. Derouet, and B. Leclercq, The digestibility of cell-wall polysaccharides from wheat (bran or whole grain), soybean meal, and white lupin meal in cockerels, Muscovy ducks, and rats. Poultry Sci. 69: FARHAT ET AL. Chavez, E. R., S. P. Touchburn, A. Farhat, L. Normand, and P. C. Laguë, Industrial food wastes transformed into human food through animal agriculture. Pages in: Research Reports, Department of Animal Science, McGill University, Montreal, QC, Canada. Cozzi, G., and C. E. Polan, Corn gluten meal or dried brewers grain as partial replacement for soybean meal in the diet of holstein cows. J. Dairy Sci. 77: El Bouchy, A.R.Y., and A.F.B. Van der Poel, Poultry Feed from Waste. Chapman and Hall, London, UK. Farhat, A., L. Normand, E. R. Chavez, S. P. Touchburn, and P. C. Laguë, Performance and carcass characteristics of Pekin and Muscovy ducks fed diets based on food wastes. Pages in: Research Reports, Department of Animal Science, McGill University, Montreal, QC, Canada. Goering, H. K., and P. J. Van Soest, Forage fiber analyses. Agriculture Handbook No Agricultural Research Service, USDA, Washington, DC. Hill, F. W., and D. L. Anderson, Comparison of metabolizable energy and productive determinations with growing chicks. J. Nutr. 64: Mohamed, K., B. Leclercq, A. Anwar, H. El-Alaily, and H. Soliman, A comparative study of metabolizable energy in ducklings and domestic chicks. Anim. Feed Sci. Technol. 11: Ostrowski-Meissner, H. T., Effect of contamination of foods by Aspergillus flavus on the nutritive value of protein. J. Sci. Food Agric. 35: Ragland, D., D. King, and O. Adeola, Determination of metabolizable energy content of feed ingredients for ducks. Poultry Sci. 76: SAS Institute, SAS/STAT User s Guide: Statistics. Version 6. 4th Edition. SAS Institute Inc., Cary, NC. Sibbald, I. R., and P. M. Morse, The effect of feed input and excreta collection time on estimates of metabolic plus endogenous energy losses in the bioassay for true metabolizable energy. Poultry Sci. 62: Sibbald, I. R., Passage of food through the adult rooster. Poultry Sci. 58: Siregar, A. P., and D. J. Farrell, A comparison of the energy and nitrogen metabolism of starved ducklings and chickens. Br. Poult. Sci. 21: Utley, P. R., and R. E. Hellwig, Feeding value of peanut skins added to bermuda grass pellets and fed to growing beef calves. J. Anim. Sci. 60(Suppl. 2): Zia-Ur-Rehman, A. Sakhawat, A. D. Khan, and F. H. Shah, Utilization of fruit and vegetable waste in layers diet. J. Sci. Food Agric. 65: