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METABOLISM AND NUTRITION |





* USDA, Agriculture Research Service, Poultry Research Unit, Mississippi State, MS 39762;
USDA, Agriculture Research Service, Swine Odor and Manure Management Research Unit, Ames, IA 50011;
Department of Poultry Science, Mississippi State University, Mississippi State, MS 39762; and
Department of Animal Science, Iowa State University, Ames 50011
4 Corresponding author: bdozier{at}msa-msstate.ars.usda.gov
| ABSTRACT |
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0.0001) and Y = 3,348.62x –140.18 (P
0.0001) for experiments 2 and 3, respectively. The AMEn of glycerin was determined as 3,621, 3,331, and 3,349 kcal/kg in experiments 1, 2, and 3, respectively. The average AMEn of glycerin across the 3 experiments was 3,434 kcal/kg, which is similar to its gross energy content. These results indicate that AMEn of glycerin is utilized efficiently by broiler chickens.
Key Words: broiler metabolizable energy glycerin
| INTRODUCTION |
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During digestion, triglycerides are hydrolyzed by pancreatic lipase to form free fatty acids and glycerol (Brody, 1994). The resulting glycerol is water soluble and freely enters the portal blood (Sambrook, 1980). Intestinal absorption of glycerol in rats has been shown to range from 70 to 89% (Hober and Hober, 1937), with the high absorption rate of glycerol likely due to its small molecular weight and it being passively absorbed rather than forming a micelle like that noted for medium and large chain fatty acids with bile salts (Guyton, 1991). Once digested, absorbed, and transferred to liver and tissues, glycerol is converted to glucose via gluconeogenesis (Emmanuel et al., 1983) or oxidized for energy production via glycolysis and the citric acid cycle (Rosebrough et al., 1980).
Several researchers have reported that glycerin is an acceptable feed ingredient for poultry (Campbell and Hill, 1962; Lessard et al., 1993; Simon et al., 1996; Cerrate et al., 2006). Adding glycerin up to an inclusion level of 5% has shown no adverse effects on growth or carcass yield (Lessard et al., 1993; Simon et al., 1996; Cerrate et al., 2006). However, increasing dietary glycerin above 10% has been shown to adversely affect growth performance and meat yield of broiler chickens (Simon et al., 1996; Cerrate et al., 2006), although this may be due to feed flowability and associated feed consumption (Cerrate et al., 2006).
Previous research has used the ME of glycerin as 95 to 100% of its gross energy (GE) in dietary formulation (Brambilla and Hill, 1966; Lin et al., 1976; Cerrate et al., 2006). To our knowledge, AMEn of glycerin with broiler chickens has not been previously reported. The objectives of this research were to determine AMEn of glycerin using broiler chickens at various ages to 1) delineate AMEn of glycerin, and 2) determine if broilers from diverse ages utilize glycerin differently.
| MATERIALS AND METHODS |
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Dietary Treatments
A single source of glycerin was added to the basal diets to create treatment diets in all experiments and contained 86.95% glycerol (Table 1
). Basal diets were formulated to meet or exceed NRC (1994) nutrient recommendations for broilers in each experiment (Table 2
). Because no dietary fat was added, all diets were formulated to be low in AMEn. In addition, all diets differed in nutrient composition due to the diverse age of broilers used in experimentation. Experimental diets were created by the addition of glycerin to the basal diet. In experiment 1, 2 dietary treatments were formulated, consisting of a control diet (100% basal diet) and a diet containing 6% glycerin (94% basal diet + 6% glycerin). In experiments 2 and 3, dietary treatments included the addition of glycerin at 0 (100% basal diet), 3% (97% basal diet + 3% glycerin), 6% (94% basal diet + 6% glycerin), or 9% (91% basal diet + 9% glycerin). Experiment 1 was a preliminary study that estimated AMEn by difference, where AMEn of the control diet was subtracted from the AMEn of the diet containing 6% glycerin. Birds were fed ad libitum. In experiments 2 and 3, broilers were fed 91, 94, 97, and 100% of ad libitum intake as determined from previous research at our laboratory. Feeding varying proportions of ad libitum intake allowed for each treatment group to consume the same amount of basal diet so differences in AMEn consumption were due to glycerin. Subsequently, AMEn intake was regressed against feed intake with the slope representing AMEn of glycerin (Adeola, 2001). One advantage of using regression analysis is that the slope estimate involves multiple inclusion levels instead of estimating from 1 level.
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Statistics
Data were statistically evaluated by the GLM and MIXED procedures (SAS, 2004) involving a randomized complete block design. Cage location was the blocking factor. Three analyses were used: 1) ANOVA with treatment means separated by the least significance comparison; 2) regression analysis to evaluate linear and quadratic effects of dietary glycerin addition; and 3) AMEnintake was regressed against feed intake to determine AMEn of glycerin. Model effects included block, diet, and block x diet (error). Statistical significance was considered at P
0.05. Observations were removed when the response criteria exceeded 2 SD from the mean.
| RESULTS |
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0.05) AMEn and AMEn intake than the control-fed birds. Feed intake, energy excretion, and BW were not affected by the dietary treatments.
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0.0001; r2 = 0.80). Gradient increments of glycerin (P
0.001) increased feed intake and gross energy intake, but final BW, energy excretion, and AMEn were not affected (Table 4
0.05) with each increment of glycerin.
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0.0001; r2 = 0.84). Progressive addition of glycerin increased (P
0.03) feed intake, gross energy intake, and AMEn (Table 5
0.05) with each incremental level of glycerin. Broilers fed 9% glycerin had higher (P
0.05) AMEn than control fedbroilers, but AMEn was similar to broilers fed either 3 or 6% glycerin.
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| DISCUSSION |
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In experiment 2, broilers fed 3% glycerin had more variability in AMEn intake (2.6 vs. 1.6% coefficient of variation) than broilers consuming diets formulated to contain 6 or 9% glycerin. The higher variability associated with 3% glycerin was probably due to the low amount test product added compared with the 2 higher treatment levels. Moreover, MEn determination can be a highly variable measurement (Dozier et al., 2001, 2003; Batal and Dale, 2006). In addition, variability associated with feed intake and excreta measurements in balance experiments can mask differences due to treatments with low inclusion levels of a test ingredient. The basis of using 3, 6, and 9% glycerin was to create treatments that would be relevant to commercial practice. It would be expected that the broiler industry would use a maximum inclusion level of 5 to 6% glycerin; hence, 3 and 6% would be within the maximum range. The 9% glycerin level was chosen to create adequate spread so an AMEn value could be determined with regression analysis. Furthermore, Cerrate et al. (2006) demonstrated that feeding glycerin at the 10% level had a negative effect on growth and carcass yield.
For comparative purposes, AMEn of glycerin is approximately 40% of poultry oil (Cullen et al., 1962; Lessire and Leclercq, 1982) and 36% of corn oil (NRC, 1994). However, AMEn of glycerin is only 10 to 12% higher than corn and grain sorghum, respectively (NRC, 1994). Hence, the energy value of glycerin is a replacement of carbohydrates and only a partial replacement of fats and oils.
In conclusion, AMEn of glycerin was efficiently utilized with an AMEn of 3,434 kcal/kg, which was very similar to its GE. Based on this research, AMEn can be assigned 92 to 95% of its GE. Future research should determine if AMEn and GE are closely related with glycerin sources derived from different feedstocks.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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2 The term glycerol is discussed when it is produced from metabolism, whereas glycerin is used when it is produced from fats and oils as a by-product of manufacturing of soaps, fatty acids, and biofuel. ![]()
3 This is a corrected PDF showing the correct spelling of the last author's name (K. Bregendahl). ![]()
Received for publication July 23, 2007. Accepted for publication October 22, 2007.
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