- Email: [email protected]
Nutrient Compostion of Feed-Grade and Pet-Food-Grade Poultry By-Product Meal
2003 Poultry Science Association, Inc.
Nutrient Compostion of Feed-Grade and Pet-Food-Grade Poultry By-Product Meal W. A. Dozier, III,*,1 N. M. Dale,† and C. R. Dove‡
Primary Audience: Nutritionists and Researchers SUMMARY Pet-food manufacturers have specified to renderers the need for poultry by-product meal (PBM) to be manufactured without lower quality by-product fractions, such as feathers and heads, leading to a higher protein product than conventional feed-grade PBM. One result is that nutritionists are faced with greater nutrient variation among PBM sources. Thirty-six PBM samples (26 = feed grade and 10 = pet-food grade) were collected from commercial feed mills during a 3-mo period to assess nutrient composition and its variation. Pet-food-grade PBM had higher protein, less ash, and lower calcium than feed-grade PBM. Amino acid analyses indicated the pet-food-grade PBM had higher lysine and methionine, and the amino acids in pet-food-grade PBM exhibited higher digestibility compared with those in the feed-grade samples. Nutrient variability was more pronounced in the feed-grade PBM. Key words: animal by-product, feedstuff, ingredient, poultry by-product meal 2003 J. Appl. Poult. Res. 12:526–530
DESCRIPTION OF PROBLEM Poultry by-product meal (PBM) is a popular protein source for poultry feeds. In the past, PBM was of reasonably consistent nutrient composition, with nutrient levels similar to those reported by the NRC [1]. However, in recent years, the pet food industry, which is willing to pay a premium for PBM of a defined composition, has placed increased demand for higher protein PBM. Meal manufactured for this market is usually termed pet-food grade, whereas the resulting segregation of materials has led to increased variation in feed-grade PBM. It is been widely suggested that feed-grade PBM, which 1
contains more variety of processing residues, is more variable than in previous years. This has decreased the economic value of the ingredient, as nutritionists must include wider margins of safety in their nutrient matrixes to reduce the likelihood that manufactured feed will have a less than intended nutrient composition. This study examined nutrient composition and its variability in currently available feedgrade and pet-food-grade sources of PBM. Measurements were extended beyond proximate composition to include amino acid profiles, an estimate of amino acid digestibility, and mineral analyses.
To whom correspondence should be addressed: [email protected].
Downloaded from http://japr.oxfordjournals.org/ at Kungl Tekniska Hogskolan Biblioteket on March 9, 2015
*Poultry Science Department, University of Georgia, Rural Development Center, PO Box 1209, Tifton, Georgia 31793; †Poultry Science Department, University of Georgia, Athens, Georgia 36849-5416; and ‡Department of Animal and Dairy Science, University of Georgia, Tifton, Georgia 31793
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TABLE 1. Proximate composition of feed-grade and pet-food-grade poultry by-product meal Feed gradeA Item, % Crude protein Ether extract Moisture Ash
Pet-food gradeB
Maximum
Minimum
Average
SD
Maximum
Minimum
Average
SD
63.7 24.5 5.6 20.6
49.3 10.5 1.7 12.8
58.1 14.4 4.2 17.1
3.2 3.1 1.3 2.4
69.3 15.1 7.2 18.5
63.0 10.9 2.2 10.7
66.1 12.6 4.1 15.1
1.9 1.6 1.4 1.6
A
Values are from 26 subsamples collected from feed mills in the southeastern United States. Values are from 10 subsamples collected from feed mills in southeastern United States.
B
Thirty-six samples (26 = feed grade and 10 = pet-food grade) were obtained from commercial feed mills located in Alabama, Delaware, Georgia, North Carolina, Tennessee, and Virginia. Subsamples were analyzed for proximate composition, mineral content, amino acid composition, and amino acid digestibility. Subsamples were prepared for proximate analysis by grinding each sub-sample in a stainless steel blade grinder until caking was observed. Percentage moisture was determined by drying 2 g of feed at 135°C for 2 h [2]. Ash content was measured by igniting 2 g of feed at 600°C for 2 h in a preweighed porcelain crucible and weighing the residue [2]. Crude protein composition was determined with 0.2 g of the subsample to measure the recovery of nitrogen [3]. Ether extract percentage was measured gravimetrically by extracting 1 g of feed dried at 105°C for 1 h with boiling petroleum ether using glass fiber thimbles [4]. The extracted fat was collected in preweighed aluminum cups, dried at 105°C, and weighed.
Inductively coupled plasma emission spectroscopy (ICP) was performed to determine mineral composition. Sample preparation included grinding subsamples in a stainless steel blade grinder until caking was observed. After grinding, 2 g of feed were digested with 10 mL of concentrated nitric acid and 5-mL of concentrated perchloric acid on a hot plate. The digestion was continued until the temperature increased to the boiling point of perchloric acid, approximately 200°C. After this digestion step, 10 mL of 25% vol/vol hydrochloric acid was added, and the digests were diluted to 100 mL with distilled-deionized water. Mineral concentrations were determined from the digested samples by using ICP [5]. Amino acid concentrations of the subsamples were determined in triplicate, after 22 h of hydrolysis (6 N HCl) by ion exchange chromatography [6]. In addition to measuring total amino acid concentrations of PBM subsamples, amino acid digestibility was estimated by Novus International using an IDEA analysis [7]. PBM subsamples were prepared for IDEA analysis by grinding to a fine powder and passing through
TABLE 2. Mineral composition of feed-grade and pet-food-grade poultry by-product meal Feed gradeA Item Calcium, % Phosphorus, % Potassium, % Magnesium, % Manganese, ppm Iron, ppm Copper, ppm Zinc, ppm Sodium, ppm A
Pet-food gradeB
Maximum
Minimum
Average
SD
Maximum
Minimum
Average
SD
6.50 3.20 0.64 0.21 19 4,626 50 114 6,660
3.10 1.50 0.33 0.11 6 406 12 65 2,961
5.17 2.50 0.51 0.15 19 1,830 22 94 4,608
1.10 0.44 0.08 0.02 4 1,480 8 14 996
6.40 3.40 0.75 0.19 14 960 430 119 5,897
2.40 1.70 0.62 0.12 5 129 4 74 3,681
4.61 2.59 0.69 0.15 9 352 57 94 4,635
1.39 0.59 0.04 0.02 3.30 302 131 15 719
Values are from 26 subsamples collected from feed mills in the southeastern United States. Values are from 10 subsamples collected from feed mills in the southeastern United States.
B
Downloaded from http://japr.oxfordjournals.org/ at Kungl Tekniska Hogskolan Biblioteket on March 9, 2015
MATERIALS AND METHODS
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TABLE 3. Amino acid composition of feed-grade and pet-food-grade poultry by-product meal Feed gradeA Concentration,C %
Maximum
Minimum
Average
SD
Maximum
Minimum
Average
SD
3.32 1.12 0.35 2.10 4.78 1.72 ... 2.34 3.70 3.80 2.07 5.65 7.33
1.77 0.46 0.07 1.16 2.51 0.80 ... 1.14 0.80 1.88 0.90 3.00 3.73
2.75 0.77 0.20 1.85 3.63 1.36 ... 1.86 1.65 3.16 1.57 4.48 5.84
0.41 0.17 0.08 0.24 0.65 0.23 ... 0.30 0.76 0.47 0.27 0.62 0.76
3.65 1.02 0.28 2.33 4.34 1.68 ... 2.33 3.23 3.87 1.84 5.67 6.77
2.48 0.63 0.14 1.61 2.94 1.12 ... 1.45 0.88 2.61 1.13 3.75 5.18
2.92 0.84 0.18 1.82 3.49 1.30 ... 1.74 1.62 3.00 1.52 4.68 5.90
0.38 0.10 0.05 0.23 0.48 0.18 ... 0.28 0.89 0.42 0.23 0.55 0.48
86.6 88.5 69.3 85.4 89.2 88.8 91.2 87.1 82.3 89.6 91.1 87.1 86.0
41.1 58.7 19.5 57.6 77.8 60.8 79.0 63.7 57.4 64.6 75.0 73.6 64.1
62.9 72.1 41.5 70.0 82.3 73.6 84.8 73.0 67.2 75.9 81.4 79.0 73.1
11.8 7.6 12.6 7.0 2.8 7.1 3.1 5.8 6.2 6.4 4.0 3.3 5.3
93.3 95.5 82.6 92.2 93.9 96.9 91.2 96.9 92.7 95.5 97.9 92.8 95.0
74.5 79.5 53.7 76.9 77.8 60.8 87.9 78.4 73.0 82.1 85.1 82.1 78.0
85.2 87.0 68.3 84.7 89.1 88.1 90.8 87.0 82.1 89.1 91.0 87.0 85.9
8.0 5.6 5.6 4.3 3.0 4.8 1.8 6.1 6.5 4.5 4.2 3.5 5.6
A
Values are from 26 subsamples collected from feed mills in the southeastern United States. Values are from 10 subsamples collected from feed mills in the southeastern United States. C Analysis was conducted in triplicate. D Amino acid digestibility was estimated using an immobilized digestive enzyme assay (Novus, IDEA system) in duplicate. B
a 1-mm mesh screen. The ground samples were solubilized in 50 mM KH2PO4, 0.1% NaN3, and 50 mM EDTA, pH 6.2, at a final concentration of 8 mg/mL. Duplicate samples (2.5 mL), including any insoluble material, were transferred to an enzyme kit [7]. Digestion was carried out on an end-to-end rotator for 2 h in a 37°C incubator. The rate of digestion was quantified by the reaction of α-amino groups with o-phthalaldehyde on initial and digested samples. An IDEA value was calculated as the rate of digestion divided by the crude protein of the sample. This value was used to calculate the predicted amino acid digestibilities estimated from equations supplied in the kit, which are based upon correlations with poultry true amino acid digestibility coefficients. All samples were performed in duplicate. A standard sample of known digestibility was included in the assay as the control.
RESULTS AND DISCUSSION Proximate compositions of the feed-grade and pet-food-grade PBM are presented in Table 1. Pet-food-grade PBM was higher in protein content (66.1 vs. 58.1%) and had less variation than the feed-grade sources. The average crude protein content of feed-grade PBM is in close agreement with that listed by the NRC [1], but individual values ranged from 49.3 to 63.7%. This extreme variation may be evidence of the diverse residues included in the rendering process. The ether extract content was also more varied with the feed-grade PBM compared with the pet-food-grade, which could indicate the inclusion of sludge in feed-grade PBM. Ash was lower with pet-food grade than feed grade but not as low as might have been expected. Average moisture contents of the 2 sources were similar;
Downloaded from http://japr.oxfordjournals.org/ at Kungl Tekniska Hogskolan Biblioteket on March 9, 2015
Lysine Methionine Cystine Threonine Arginine Isoleucine Tryptophan Valine Histidine Leucine Phenylalanine Glycine Glutamic acid Digestibility,D % Lysine Methionine Cystine Threonine Arginine Isoleucine Tryptophan Valine Histidine Leucine Phenylalanine Glycine Glutamic acid
Pet-food gradeB
DOZIER ET AL.: FEED-GRADE VS. PET-FOOD-GRADE MEAL
529
however, the feed-grade source had several values that were considered to be extremely low (<5%). Mineral contents are noted in Table 2. In agreement with ash composition, calcium content and its variation were lower for the petfood-grade PBM than feed-grade sources, but the converse occurred with phosphorus. The cause of the inverse relationship in calcium and phosphorus of pet-food-grade PBM relative to its ash content is elusive. Manganese and iron contents were higher in the feed-grade PBM than in the pet-food sources, and extensive variation was observed for the feed-grade PBM. The large disparity in iron contents between the 2 sources may suggest impurities associated with the inclusion of sludge in rendering the feed-grade source. Iron sulfate is frequently used as a flocculating agent in processing plant water purification. The pet-food-grade source had higher copper content than feed-grade PBM. Amino acid composition indicated that petfood-grade PBM sources had higher total con-
centrations of lysine, methionine, glycine, and glutamic acid than the feed-grade sources (Table 3). Lysine and methionine were lower in the present study (regardless of source) than reported by NRC [1] (lysine = 3.10% and methionine = 0.99%). The digestibility of amino acids was less for the feed-grade PBM, and variability was more pronounced (Table 3). In comparison with values reported by the NRC [1], average amino acid digestibility coefficients were lower for the feed-grade sources. Several feed-grade PBM samples had a low moisture content (<5%), which may indicate that some of the variability associated with digestible lysine might have been due to overprocessing during rendering. The digestible lysine coefficient increased with higher moisture in feed-grade PBM (Figure 1). Lysine digestibility did not appear to be related to moisture content in pet-food-grade PBM, because low moisture content (<5%) was not as common with this source of PBM. Use of a trend line revealed that the reduction in lysine digestibility was not apparent with samples having at least 5% moisture.
CONCLUSIONS AND APPLICATIONS 1. Pet-food-grade PBM had a higher protein content, lower ether extract, and lower ash composition than feed-grade product. The feed-grade sources were more variable in proximate composition.
Downloaded from http://japr.oxfordjournals.org/ at Kungl Tekniska Hogskolan Biblioteket on March 9, 2015
FIGURE 1. Relation between moisture content and lysine digestibility in feed-grade poultry by-product meal.
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2. Pet-food-grade PBM had lower calcium content and higher phosphorus composition compared with the feed-grade source. 3. Lysine and methionine compositions were higher in pet-food-grade PBM. Pet-food-grade PBM also had a higher amino acid digestibility. Lysine digestibility appeared to be influenced by the moisture content of the feed-grade sources.
REFERENCES AND NOTES
2. AOAC. 1996. Official Methods of Analysis of AOAC International. 16th ed. AOAC International, Gathersburg, MD. 3. Combustion nitrogen analyzer, Elementar Americus Inc., Mt. Laurel, NJ. 4. Tecator-Soxtec fat extractor. Tecator, Herndon, VA.
5. Maxfield, R., and B. Mindak. 1985. EPA Method Study 27, Method 200.7. EPA- 600/S4-85/05. Natl. Tech. Inf. Service, Springfield, VA. 6. Beckman 6300 Amino Acid Analyzer, Beckman Instruments, Palo Alto, CA. 7. PC IDEA Kit, Novus Int., St. Louis, MO.
Downloaded from http://japr.oxfordjournals.org/ at Kungl Tekniska Hogskolan Biblioteket on March 9, 2015
1. National Research Council. 1994. Nutrient Requirements of Poultry. 9th ed. National Academy Press, Washington, DC.
Nutrient Compostion of Feed-Grade and Pet-Food-Grade Poultry By-Product Meal W. A. Dozier, III,*,1 N. M. Dale,† and C. R. Dove‡
Primary Audience: Nutritionists and Researchers SUMMARY Pet-food manufacturers have specified to renderers the need for poultry by-product meal (PBM) to be manufactured without lower quality by-product fractions, such as feathers and heads, leading to a higher protein product than conventional feed-grade PBM. One result is that nutritionists are faced with greater nutrient variation among PBM sources. Thirty-six PBM samples (26 = feed grade and 10 = pet-food grade) were collected from commercial feed mills during a 3-mo period to assess nutrient composition and its variation. Pet-food-grade PBM had higher protein, less ash, and lower calcium than feed-grade PBM. Amino acid analyses indicated the pet-food-grade PBM had higher lysine and methionine, and the amino acids in pet-food-grade PBM exhibited higher digestibility compared with those in the feed-grade samples. Nutrient variability was more pronounced in the feed-grade PBM. Key words: animal by-product, feedstuff, ingredient, poultry by-product meal 2003 J. Appl. Poult. Res. 12:526–530
DESCRIPTION OF PROBLEM Poultry by-product meal (PBM) is a popular protein source for poultry feeds. In the past, PBM was of reasonably consistent nutrient composition, with nutrient levels similar to those reported by the NRC [1]. However, in recent years, the pet food industry, which is willing to pay a premium for PBM of a defined composition, has placed increased demand for higher protein PBM. Meal manufactured for this market is usually termed pet-food grade, whereas the resulting segregation of materials has led to increased variation in feed-grade PBM. It is been widely suggested that feed-grade PBM, which 1
contains more variety of processing residues, is more variable than in previous years. This has decreased the economic value of the ingredient, as nutritionists must include wider margins of safety in their nutrient matrixes to reduce the likelihood that manufactured feed will have a less than intended nutrient composition. This study examined nutrient composition and its variability in currently available feedgrade and pet-food-grade sources of PBM. Measurements were extended beyond proximate composition to include amino acid profiles, an estimate of amino acid digestibility, and mineral analyses.
To whom correspondence should be addressed: [email protected].
Downloaded from http://japr.oxfordjournals.org/ at Kungl Tekniska Hogskolan Biblioteket on March 9, 2015
*Poultry Science Department, University of Georgia, Rural Development Center, PO Box 1209, Tifton, Georgia 31793; †Poultry Science Department, University of Georgia, Athens, Georgia 36849-5416; and ‡Department of Animal and Dairy Science, University of Georgia, Tifton, Georgia 31793
DOZIER ET AL.: FEED-GRADE VS. PET-FOOD-GRADE MEAL
527
TABLE 1. Proximate composition of feed-grade and pet-food-grade poultry by-product meal Feed gradeA Item, % Crude protein Ether extract Moisture Ash
Pet-food gradeB
Maximum
Minimum
Average
SD
Maximum
Minimum
Average
SD
63.7 24.5 5.6 20.6
49.3 10.5 1.7 12.8
58.1 14.4 4.2 17.1
3.2 3.1 1.3 2.4
69.3 15.1 7.2 18.5
63.0 10.9 2.2 10.7
66.1 12.6 4.1 15.1
1.9 1.6 1.4 1.6
A
Values are from 26 subsamples collected from feed mills in the southeastern United States. Values are from 10 subsamples collected from feed mills in southeastern United States.
B
Thirty-six samples (26 = feed grade and 10 = pet-food grade) were obtained from commercial feed mills located in Alabama, Delaware, Georgia, North Carolina, Tennessee, and Virginia. Subsamples were analyzed for proximate composition, mineral content, amino acid composition, and amino acid digestibility. Subsamples were prepared for proximate analysis by grinding each sub-sample in a stainless steel blade grinder until caking was observed. Percentage moisture was determined by drying 2 g of feed at 135°C for 2 h [2]. Ash content was measured by igniting 2 g of feed at 600°C for 2 h in a preweighed porcelain crucible and weighing the residue [2]. Crude protein composition was determined with 0.2 g of the subsample to measure the recovery of nitrogen [3]. Ether extract percentage was measured gravimetrically by extracting 1 g of feed dried at 105°C for 1 h with boiling petroleum ether using glass fiber thimbles [4]. The extracted fat was collected in preweighed aluminum cups, dried at 105°C, and weighed.
Inductively coupled plasma emission spectroscopy (ICP) was performed to determine mineral composition. Sample preparation included grinding subsamples in a stainless steel blade grinder until caking was observed. After grinding, 2 g of feed were digested with 10 mL of concentrated nitric acid and 5-mL of concentrated perchloric acid on a hot plate. The digestion was continued until the temperature increased to the boiling point of perchloric acid, approximately 200°C. After this digestion step, 10 mL of 25% vol/vol hydrochloric acid was added, and the digests were diluted to 100 mL with distilled-deionized water. Mineral concentrations were determined from the digested samples by using ICP [5]. Amino acid concentrations of the subsamples were determined in triplicate, after 22 h of hydrolysis (6 N HCl) by ion exchange chromatography [6]. In addition to measuring total amino acid concentrations of PBM subsamples, amino acid digestibility was estimated by Novus International using an IDEA analysis [7]. PBM subsamples were prepared for IDEA analysis by grinding to a fine powder and passing through
TABLE 2. Mineral composition of feed-grade and pet-food-grade poultry by-product meal Feed gradeA Item Calcium, % Phosphorus, % Potassium, % Magnesium, % Manganese, ppm Iron, ppm Copper, ppm Zinc, ppm Sodium, ppm A
Pet-food gradeB
Maximum
Minimum
Average
SD
Maximum
Minimum
Average
SD
6.50 3.20 0.64 0.21 19 4,626 50 114 6,660
3.10 1.50 0.33 0.11 6 406 12 65 2,961
5.17 2.50 0.51 0.15 19 1,830 22 94 4,608
1.10 0.44 0.08 0.02 4 1,480 8 14 996
6.40 3.40 0.75 0.19 14 960 430 119 5,897
2.40 1.70 0.62 0.12 5 129 4 74 3,681
4.61 2.59 0.69 0.15 9 352 57 94 4,635
1.39 0.59 0.04 0.02 3.30 302 131 15 719
Values are from 26 subsamples collected from feed mills in the southeastern United States. Values are from 10 subsamples collected from feed mills in the southeastern United States.
B
Downloaded from http://japr.oxfordjournals.org/ at Kungl Tekniska Hogskolan Biblioteket on March 9, 2015
MATERIALS AND METHODS
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528
TABLE 3. Amino acid composition of feed-grade and pet-food-grade poultry by-product meal Feed gradeA Concentration,C %
Maximum
Minimum
Average
SD
Maximum
Minimum
Average
SD
3.32 1.12 0.35 2.10 4.78 1.72 ... 2.34 3.70 3.80 2.07 5.65 7.33
1.77 0.46 0.07 1.16 2.51 0.80 ... 1.14 0.80 1.88 0.90 3.00 3.73
2.75 0.77 0.20 1.85 3.63 1.36 ... 1.86 1.65 3.16 1.57 4.48 5.84
0.41 0.17 0.08 0.24 0.65 0.23 ... 0.30 0.76 0.47 0.27 0.62 0.76
3.65 1.02 0.28 2.33 4.34 1.68 ... 2.33 3.23 3.87 1.84 5.67 6.77
2.48 0.63 0.14 1.61 2.94 1.12 ... 1.45 0.88 2.61 1.13 3.75 5.18
2.92 0.84 0.18 1.82 3.49 1.30 ... 1.74 1.62 3.00 1.52 4.68 5.90
0.38 0.10 0.05 0.23 0.48 0.18 ... 0.28 0.89 0.42 0.23 0.55 0.48
86.6 88.5 69.3 85.4 89.2 88.8 91.2 87.1 82.3 89.6 91.1 87.1 86.0
41.1 58.7 19.5 57.6 77.8 60.8 79.0 63.7 57.4 64.6 75.0 73.6 64.1
62.9 72.1 41.5 70.0 82.3 73.6 84.8 73.0 67.2 75.9 81.4 79.0 73.1
11.8 7.6 12.6 7.0 2.8 7.1 3.1 5.8 6.2 6.4 4.0 3.3 5.3
93.3 95.5 82.6 92.2 93.9 96.9 91.2 96.9 92.7 95.5 97.9 92.8 95.0
74.5 79.5 53.7 76.9 77.8 60.8 87.9 78.4 73.0 82.1 85.1 82.1 78.0
85.2 87.0 68.3 84.7 89.1 88.1 90.8 87.0 82.1 89.1 91.0 87.0 85.9
8.0 5.6 5.6 4.3 3.0 4.8 1.8 6.1 6.5 4.5 4.2 3.5 5.6
A
Values are from 26 subsamples collected from feed mills in the southeastern United States. Values are from 10 subsamples collected from feed mills in the southeastern United States. C Analysis was conducted in triplicate. D Amino acid digestibility was estimated using an immobilized digestive enzyme assay (Novus, IDEA system) in duplicate. B
a 1-mm mesh screen. The ground samples were solubilized in 50 mM KH2PO4, 0.1% NaN3, and 50 mM EDTA, pH 6.2, at a final concentration of 8 mg/mL. Duplicate samples (2.5 mL), including any insoluble material, were transferred to an enzyme kit [7]. Digestion was carried out on an end-to-end rotator for 2 h in a 37°C incubator. The rate of digestion was quantified by the reaction of α-amino groups with o-phthalaldehyde on initial and digested samples. An IDEA value was calculated as the rate of digestion divided by the crude protein of the sample. This value was used to calculate the predicted amino acid digestibilities estimated from equations supplied in the kit, which are based upon correlations with poultry true amino acid digestibility coefficients. All samples were performed in duplicate. A standard sample of known digestibility was included in the assay as the control.
RESULTS AND DISCUSSION Proximate compositions of the feed-grade and pet-food-grade PBM are presented in Table 1. Pet-food-grade PBM was higher in protein content (66.1 vs. 58.1%) and had less variation than the feed-grade sources. The average crude protein content of feed-grade PBM is in close agreement with that listed by the NRC [1], but individual values ranged from 49.3 to 63.7%. This extreme variation may be evidence of the diverse residues included in the rendering process. The ether extract content was also more varied with the feed-grade PBM compared with the pet-food-grade, which could indicate the inclusion of sludge in feed-grade PBM. Ash was lower with pet-food grade than feed grade but not as low as might have been expected. Average moisture contents of the 2 sources were similar;
Downloaded from http://japr.oxfordjournals.org/ at Kungl Tekniska Hogskolan Biblioteket on March 9, 2015
Lysine Methionine Cystine Threonine Arginine Isoleucine Tryptophan Valine Histidine Leucine Phenylalanine Glycine Glutamic acid Digestibility,D % Lysine Methionine Cystine Threonine Arginine Isoleucine Tryptophan Valine Histidine Leucine Phenylalanine Glycine Glutamic acid
Pet-food gradeB
DOZIER ET AL.: FEED-GRADE VS. PET-FOOD-GRADE MEAL
529
however, the feed-grade source had several values that were considered to be extremely low (<5%). Mineral contents are noted in Table 2. In agreement with ash composition, calcium content and its variation were lower for the petfood-grade PBM than feed-grade sources, but the converse occurred with phosphorus. The cause of the inverse relationship in calcium and phosphorus of pet-food-grade PBM relative to its ash content is elusive. Manganese and iron contents were higher in the feed-grade PBM than in the pet-food sources, and extensive variation was observed for the feed-grade PBM. The large disparity in iron contents between the 2 sources may suggest impurities associated with the inclusion of sludge in rendering the feed-grade source. Iron sulfate is frequently used as a flocculating agent in processing plant water purification. The pet-food-grade source had higher copper content than feed-grade PBM. Amino acid composition indicated that petfood-grade PBM sources had higher total con-
centrations of lysine, methionine, glycine, and glutamic acid than the feed-grade sources (Table 3). Lysine and methionine were lower in the present study (regardless of source) than reported by NRC [1] (lysine = 3.10% and methionine = 0.99%). The digestibility of amino acids was less for the feed-grade PBM, and variability was more pronounced (Table 3). In comparison with values reported by the NRC [1], average amino acid digestibility coefficients were lower for the feed-grade sources. Several feed-grade PBM samples had a low moisture content (<5%), which may indicate that some of the variability associated with digestible lysine might have been due to overprocessing during rendering. The digestible lysine coefficient increased with higher moisture in feed-grade PBM (Figure 1). Lysine digestibility did not appear to be related to moisture content in pet-food-grade PBM, because low moisture content (<5%) was not as common with this source of PBM. Use of a trend line revealed that the reduction in lysine digestibility was not apparent with samples having at least 5% moisture.
CONCLUSIONS AND APPLICATIONS 1. Pet-food-grade PBM had a higher protein content, lower ether extract, and lower ash composition than feed-grade product. The feed-grade sources were more variable in proximate composition.
Downloaded from http://japr.oxfordjournals.org/ at Kungl Tekniska Hogskolan Biblioteket on March 9, 2015
FIGURE 1. Relation between moisture content and lysine digestibility in feed-grade poultry by-product meal.
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2. Pet-food-grade PBM had lower calcium content and higher phosphorus composition compared with the feed-grade source. 3. Lysine and methionine compositions were higher in pet-food-grade PBM. Pet-food-grade PBM also had a higher amino acid digestibility. Lysine digestibility appeared to be influenced by the moisture content of the feed-grade sources.
REFERENCES AND NOTES
2. AOAC. 1996. Official Methods of Analysis of AOAC International. 16th ed. AOAC International, Gathersburg, MD. 3. Combustion nitrogen analyzer, Elementar Americus Inc., Mt. Laurel, NJ. 4. Tecator-Soxtec fat extractor. Tecator, Herndon, VA.
5. Maxfield, R., and B. Mindak. 1985. EPA Method Study 27, Method 200.7. EPA- 600/S4-85/05. Natl. Tech. Inf. Service, Springfield, VA. 6. Beckman 6300 Amino Acid Analyzer, Beckman Instruments, Palo Alto, CA. 7. PC IDEA Kit, Novus Int., St. Louis, MO.
Downloaded from http://japr.oxfordjournals.org/ at Kungl Tekniska Hogskolan Biblioteket on March 9, 2015
1. National Research Council. 1994. Nutrient Requirements of Poultry. 9th ed. National Academy Press, Washington, DC.