Download Chemical composition, protein quality, palatability, and digestibility

Chemical composition, protein quality, palatability, and digestibility
of alternative protein sources for dogs
J. M. Dust*, C. M. Grieshop*, C. M. Parsons*, L. K. Karr-Lilienthal*, C. S. Schasteen†,
J. D. Quigley, III‡, N. R. Merchen*, and G. C. Fahey, Jr.*1
*University of Illinois at Urbana-Champaign, Urbana 61801; †Novus International, Inc.,
St. Charles, MO 63304; and ‡APC, Ankeny, IA 50021
ABSTRACT: The chemical composition and protein
quality of 11 alternative protein sources (chicken products, blood products, enzyme-hydrolyzed fish protein
concentrate, soybean meal, and spray-dried pork liver)
were determined, and an experiment was conducted to
determine palatability and digestibility of processed red
blood cell-containing diets. Chicken protein sources differed in concentrations of CP, acid-hydrolyzed fat, and
total AA (TAA) by 20, 31, and 24%, respectively, and
GE by 1.7 kcal/g. Blood protein sources varied little in
acid-hydrolyzed fat and GE concentrations, but concentrations of CP and TAA differed by 11 and 8%, respectively. Protein solubility of chicken and blood protein
source categories averaged 57 and 69%, respectively.
Protein solubility of enzyme-hydrolyzed fish protein
concentrate, soybean meal, and spray-dried pork liver
was 53, 67, and 26%, respectively. Based on calculations
from immobilized digestive enzyme assay values, lysine
digestibility averaged approximately 80.4 and 81.7% for
blood and chicken protein sources, respectively. Lysine
digestibility values for soybean meal and spray-dried
pork liver were 89 and 77%, respectively. A chick protein efficiency ratio (PER) assay showed that chicken
protein sources had high protein quality values, as the
PER ranged from 2.7 to 5.3, whereas blood protein
sources had poor protein quality (PER values less than
1.5). Enzyme-hydrolyzed fish protein concentrate,
spray-dried pork liver, and soybean meal had high protein quality (PER values greater than 2.8). In the dog
palatability and digestibility experiments, a corn and
chicken-based diet supplemented with either 0 or 3%
processed red blood cells was tested. The palatability
test showed that dogs consumed more of the diet that
contained 0% vs. 3% processed red blood cells. The intake ratio for the 3% processed red blood cells diet was
0.34. Nutrient digestibilities did not differ, except for
CP, where the digestibility was greater (P = 0.01) for
dogs consuming the 0% processed red blood cells diet.
These data suggest that chemical composition and quality of alternative protein sources differ greatly among
ingredients within the same category. Palatability data
suggest that a processed red blood cells-containing diet
is not highly palatable but, when this diet was offered
as only one food, dogs demonstrated no aversion response but some decrease in protein digestion.
Key Words: Digestibility, Dog, Palatability, Protein Efficiency Ratio, Protein Quality, Protein Sources
2005 American Society of Animal Science. All rights reserved.
Introduction
A key component of canine diets is the protein source
used. Protein contains essential AA as well as nonessential AA that are used for energy, muscle deposition, and
metabolic functions of the body. The quantity of protein
required by a dog is age-dependent (AAFCO, 2003). A
puppy has a greater demand for protein, as its body is
1
Correspondence: 166 Animal Sciences Laboratory, 1207 W. Gregory Dr. (phone: 217-333-2361; fax: 217-244-3169; e-mail: gcfahey@
express.cites.uiuc.edu).
Received April 29, 2004.
Accepted June 20, 2005.
J. Anim. Sci. 2005. 83:2414–2422
growing rapidly and a large amount of muscle is being
deposited. In contrast, an adult dog requires less protein to maintain muscle mass and body metabolism
(NRC, 1985).
Today’s pet food industry is growing rapidly, with
pet owners demanding high-quality diets for their pets.
This demand is creating a search for alternative protein
sources that may be included in diets to meet the AA
requirements of the animal, to serve as palatants, and/
or to enhance the immune status of the animal. The
pet food industry traditionally has used a wide range of
protein sources, including meat and bone meals, poultry
meals, poultry by-product meals, and soybean meal
(AAFCO, 2003). Alternative protein sources that have
been studied in other animal species, but only to a
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Alternative protein sources for dogs
limited extent in companion animals, include spraydried plasma (Quigley et al., 2004), wheat protein, fish
protein, and processed red blood cells.
By expanding the database on compositional analyses of alternative protein sources and by determining
their quality, their ability to enhance palatability, and
their immunomodulatory role, nutritionists will be able
to use these alternative ingredients in dietary formulations for pets to optimal advantage. Therefore, the objective of this study was to determine the chemical composition and protein quality of several alternative protein sources. In addition, an experiment to determine
the palatability and digestibility of one of these sources,
processed red blood cells, as a component of dog diets
was conducted.
Materials and Methods
Substrates
Eleven spray-dried or conventional protein sources
were tested. Chicken protein sources included spraydried cooked chicken from deboned USDA-inspected
chicken parts used for pet food applications that is then
spray dried to form a powder (American Dehydrated
Foods, Inc., Springfield, MO); spray-dried cooked
chicken liver produced from USDA-inspected facilities
using chicken livers that are ground, cooked, and spraydried (American Dehydrated Foods, Inc.); spray-dried
egg processed from pasteurized whole egg solids, and
then spray dried to form a granulated powder (American Dehydrated Foods, Inc.); chicken-by-product meal
(Tyson Foods, Inc., Springdale, AR) comprising ground,
cleaned, rendered carcass parts of chicken with trace
amounts of feathers and blood (AAFCO, 2003); and
poultry by-product meal (Tyson Foods, Inc.) comprising
ground, cleaned, rendered carcass parts of poultry including heads, feet, and viscera, to include trace
amounts of feathers and blood (AAFCO, 2003).
The blood protein sources included processed red
blood cells (American Protein Corp., Inc., Ankeny, IA)
obtained from blood collected from abattoirs and centrifuged to separate the red blood cells from the plasma.
The red blood cells are then processed using a proprietary procedure to produce a cream colored powder.
Spray-dried plasma (American Protein Corp., Inc.) is a
product of blood collected from abattoirs and centrifuged to separate the plasma fraction from the red blood
cells. The plasma is then spray dried, producing a powder. Spray-dried whole beef blood (California Spray Dry
Co., Stockton, CA) is whole blood with approximately
20% solids that is spray dried to form a free-flowing
powder.
Other protein sources tested included enzyme-hydrolyzed fish protein concentrate (California Spray Dry
Co.), which is fish remaining after filleting that are then
subjected to controlled proteolytic enzyme digestion
that hydrolyzes the CP into peptides and free AA. Soybean meal (SBM) is a common plant protein source
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produced by removing the oil from soybeans and grinding the residue into a meal form. Spray-dried pork liver
(California Spray Dry Co.) is pork liver from USDAinspected facilities that undergoes a solubilization process at a regulated temperature, time, and pH, followed
by enzymatic hydrolysis, pasteurization, and spray
drying.
The SBM was ground with dry ice to pass 2- and 0.5mm screens in a model 4 Wiley mill (Thomas-Wiley,
Swedesboro, NJ) in preparation for chemical analyses.
Other protein products already were finely ground and
required no further processing.
Chemical Analyses
Each protein source was analyzed for DM, OM, ash
(AOAC, 1985), CP (AOAC, 1995) using a Leco nitrogen/
protein determinator (model FP-2000; Leco Corp., St.
Joseph, MI), acid-hydrolyzed fat (Budde, 1952; AACC,
1983), and GE (Parr Instrument Manuals, Parr Instrument Co., Moline, IL). The 11 protein sources were analyzed for AA concentrations using a Beckman 6300 AA
analyzer (Beckman Coulter, Inc., Fullerton, CA, according to AOAC, 1995) at the University of Missouri
Experiment Station Chemical Laboratories. The reported AA concentrations were not corrected for incomplete recovery resulting from hydrolysis. All ingredients
were analyzed in duplicate to provide a snapshot of
protein availability by in vitro methods. Analyses were
repeated if deviation of greater than 5% occurred among
duplicates for all components present at a concentration
greater or equal to 10%. Analyses were repeated if a
deviation of greater than 10% occurred among duplicates for all components present at a concentration of
less than 10%.
Protein Quality Assays
A protein solubility in potassium hydroxide assay
(Araba and Dale, 1990) and the immobilized digestive
enzyme assay (IDEA; Schasteen et al., 2002) were conducted on each protein source. A protein efficiency ratio
(PER) assay was conducted utilizing 220, 8-d-old female chicks (New Hampshire × Columbian cross). The
average initial BW was 91.8 g/chick. Chicks were
housed in groups of five in starter batteries with raised
wire floors in an environmentally regulated room.
Eleven diets were formulated to contain one of the 11
protein sources in an otherwise N-free diet to provide
10% CP (Johnston and Coon, 1979). Composition of the
diets is presented in Table 1. The experiment was a
completely randomized design including 11 treatments,
with four replications and five chicks per replication.
The chicks were allowed ad libitum access to food and
water over the 9-d assay period. Initial and final BW
were recorded. Food consumption was recorded for calculation of G:F and PER. Data were analyzed as a completely randomized design using ANOVA in SAS (Version 8, SAS Inst., Inc., Cary, NC). Treatment differences
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Dust et al.
Table 1. Chick protein efficiency ratio (PER) assay diet
used to evaluate alternative protein sources
Ingredient
Cornstarch:dextrose (2:1 ratio)
Protein sourcesa
Soybean oil
Limestone
Dicalcium phosphate
Sodium chloride
MgSO4ⴢ7H2O
K2CO3
Purified vitamin mixbc
Mineral mixd
Purified choline chloridec
Ethoxyquin
DL-Tocopherol acetate
%, as-is basis
To 100
To provide 10% CP
5.0
1.22
2.45
0.50
0.35
0.90
0.20
0.15
0.20
0.0125
0.002
a
Protein sources (% incorporated into diet): chicken by-product meal
(15.92%), poultry by-product meal (15.60%), spray-dried cooked
chicken (20.35%), spray-dried cooked chicken liver (14.49%), spraydried egg product (18.96%), processed red blood cells (10.50%), spraydried plasma (11.85%), spray-dried whole beef blood (10.47%), enzyme-hydrolyzed fish protein concentrate (16.06%), soybean meal
(19.63%), and spray-dried pork liver (14.36%).
b
Provided per kilogram of diet: thiamin, 20 mg; niacin, 50 mg;
riboflavin, 10 mg; Ca-pantothenate, 30 mg; vitamin B12, 0.04 mg;
pyridoxine, 6 mg; biotin, 0.6 mg; folic acid, 4 mg; vitamin K, 2 mg;
vitamin D, 15 ␮g; vitamin A, 1,789 ␮g; vitamin C, 250 mg.
c
Choline chloride and vitamin mix in a carrier with little to no
nitrogen-containing compounds were incorporated to provide an otherwise nitrogen-free diet except for nitrogen from test ingredients.
d
Provided per kilogram of diet: Mn (as MnO), 75 mg; Fe (as FeSO4∋H2O), 75 mg; Zn (as ZnO), 75 mg; Cu (as CuSO4ⴢ5H2O), 8 mg; I
(as CaI2), 0.75 mg; Se (as Na2SeO3), 0.3 mg.
were determined using the LSD calculated from the
pooled SEM from ANOVA. A probability of P < 0.05
was considered statistically significant.
Palatability Experiment
Twenty beagle dogs (seven males and 13 females)
with BW ranging from 6.3 to 19.9 kg were used. Dogs
were individually housed in indoor-outdoor pens measuring approximately 1.2 × 1.5 m indoors and 1.2 × 3.0
m outdoors at Kennelwood, Inc., Champaign, IL. Dogs
had access to the outside area of the kennel once daily
for an average of 2 to 4 h, depending on weather conditions. Two diets were formulated representing a cornand chicken-based canine diet supplemented with either 0 or 3% processed red blood cells. Composition of
the diets is presented in Table 2. Diets were formulated
to be isocaloric. Dietary ingredients were identical except for supplementation of processed red blood cells in
place of corn gluten meal. Diets were an extruded kibble, with the processed red blood cells being incorporated into the mixture before extrusion. The experiment
was designed as a two-bowl, free-choice test, the most
common palatability test in the petfood industry
(Griffen, 2003). This design results in the most reliable
data (Hutton, 2002). Dogs were on test for 4 d. All dogs
were allowed free access to water. Dogs were offered
500 g each of the 0% processed red blood cells diet and
the 3% processed red blood cells diet in separate bowls
Table 2. Ingredient composition of diets containing processed red blood cells (PRBC) for palatability and digestibility experiments with dogs (%, as-is basis)
Dietary treatment
Ingredient
Corn, ground
Poultry by-product meal
Brewer’s rice
Soybean meal, dehulled
Corn gluten meal
Processed red blood cells
Beet pulp
Poultry fat
KCl
NaCl
Choline chloridea
Vitamin premixb
Mineral premixc
Ethoxyquin
0% PRBC
3% PRBC
44.47
15.40
14.50
12.00
4.15
—
4.00
4.00
0.60
0.50
0.13
0.12
0.12
0.02
45.62
15.40
14.50
12.00
—
3.00
4.00
4.00
0.60
0.50
0.13
0.12
0.12
0.02
a
Provided per kilogram of diet: choline, 780 mg.
Provided per kilogram of diet: vitamin A, 14,970 IU; vitamin D3,
900 IU; vitamin E, 59.88 IU; vitamin K, 0.60 mg; thiamin, 11.98 mg;
riboflavin, 9.58 mg; pantothenic acid, 17.96 mg; niacin, 44.91 mg;
pyridoxine, 11.98 mg; biotin, 0.11 mg; folic acid, 0.72 mg; vitamin
B12, 0.02 mg.
c
Provided per kilogram of diet: Mn (as MnSO4), 12 mg; Fe (as
FeSO4), 90 mg; Cu (as CuSO4), 12 mg; Co (as CoSO4), 2.4 mg; Zn (as
ZnSO4), 120 mg; I (as KI), 1.5 mg; Se (as Na2SeO3), 0.24 mg.
b
for 1 h daily. The placement of the bowls was alternated
each day to eliminate any bowl placement bias by the
dogs. First-choice and first-approach data were collected. At the end of the hour, any refused food was
weighed to determine food intake of each diet. A sample
was taken of each diet and frozen at −4°C for subsequent
analyses. Diets were ground with dry ice to pass a 2mm screen in a model 4 Wiley mill (Thomas-Wiley) in
preparation for chemical analyses. Samples of each diet
and the processed red blood cells ingredient were taken
and analyzed for DM, OM, ash, CP, acid-hydrolyzed fat,
and GE as in chemical analysis section. The quantity of
each diet consumed was calculated by subtracting food
refusal from amount of food originally offered. Intake
ratio (IR) was calculated by dividing the grams consumed of the 3% processed red blood cells diet by the
total grams consumed of both diets. Corrected intake
ratio was calculated as intake ratio minus 0.5, to indicate a diet preference. An intake ratio of 0.5 indicates
no preference; therefore, the corrected intake ratio will
detect whether there was a diet preference significantly
different from zero.
Data were analyzed using the Mixed procedure of
SAS. The model contained the fixed effect of diet and
the random effect of dog. A probability of P < 0.05 was
considered statistically significant.
Digestibility Experiment
Fourteen beagle dogs that were 2 to 11 yr of age and
ranged in BW from 6.8 to 15.5 kg were used. Dogs were
individually housed in indoor-outdoor pens measuring
Alternative protein sources for dogs
approximately 1.2 × 1.5 m indoors and 1.2 × 3.0 m
outdoors at Kennelwood, Inc. As in the palatablity experiment, dogs had access to the outside area of the
kennel once daily for an average of 2 to 4 h, depending
on weather conditions.
Diets were the same as ones tested in the palatability
experiment (Table 2). Dogs were fed 500 g of the appropriate diet once daily, and food intake was measured
daily. Any food refusal during the digestibility trial was
collected and weighed daily. Water was provided for ad
libitum consumption throughout the study.
Dogs participated in a 20-d (two 10-d periods) digestibility experiment, in which each dog received the control (Period 1, n = 6; Period 2, n = 8) and processed red
blood cells (Period 1, n = 8; Period 2, n = 6)-containing
diet in a crossover design. Within each period, dogs
were allowed a 7-d diet adaptation phase, after which
a 3-d total fecal collection was conducted for determination of nutrient digestibilities.
A sample was taken of each diet and frozen at −4°C
for subsequent analyses. Diets were ground with dry
ice, to avoid loss of lipid, to pass a 2-mm screen in a
model 4 Wiley mill (Thomas-Wiley) in preparation for
chemical analyses. Samples of the processed red blood
cells, food, and fecal samples were prepared and analyzed as in palatability trial.
Feces were scored and weighed at the time of collection. Scoring was determined using the following system: 1 = hard, dry pellets – small, hard mass; 2 = hard,
formed, dry stool – remains firm and soft; 3 = soft,
formed moist – softer stool that retains shape; 4 = soft,
unformed – stool assumes shape of container; and 5 =
watery – liquid that can be poured. Feces were frozen
at −4°C and composited by dog at the end of each collection. All fecal samples were dried at 57°C and ground
to pass a 2-mm screen in a model 4 Wiley mill
(Thomas-Wiley).
Data were analyzed in a crossover design using the
Mixed procedure of SAS. The model contained the fixed
effects of diet and period and the random effect of dog.
A probability level of P < 0.05 was considered statistically significant.
Results and Discussion
Dry matter, OM, CP, acid-hydrolyzed fat, GE, and
AA concentrations of protein sources are presented in
Tables 3, 4, and 5. Dry matter values for the chicken
protein sources (Table 3) varied little. Organic matter
concentrations ranged from 87 to 94%. Crude protein
concentrations ranged from 49.2% (spray-dried cooked
chicken) to 69.0% (spray-dried cooked chicken liver).
Acid-hydrolyzed fat content varied from 18.3%
(chicken-by product meal) to 49.5% (spray-dried cooked
chicken). Gross energy content was lowest for chicken
by-product meal and poultry by-product meal and highest for spray-dried cooked chicken. Chicken by-product
meal, poultry by-product meal, and spray-dried egg
were similar in total essential amino acid (TEAA) com-
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position. Spray-dried cooked chicken liver had the
greatest TEAA and spray-dried cooked chicken the
least. Spray-dried cooked chicken had lower arginine,
leucine, and phenylalanine concentrations than the
other chicken protein sources. Chicken by-product meal
had the greatest total nonessential amino acid
(TNEAA) concentration (39.2%) and spray-dried
cooked chicken the least (22.0%). Chicken by-product
meal and poultry by-product meal were highest in glycine, proline, and hydroxyproline content. This result
is perhaps indicative of the connective tissue content
of these by-products compared with the other chicken
protein sources.
Poultry by-product meal has been reported to have
CP concentrations ranging from 61.9 to 74.5% (Johnson
and Parsons, 1997; Murray et al., 1997; Clapper et al.,
2001). The CP values for chicken-by product meal and
poultry by-product meal used in the present study fall
within this range, with values being closest to those
reported by Johnson and Parsons (1997). Fat concentrations in the present study were greater than those reported by Murray et al. (1997) and Clapper et al. (2001).
Batch variation is likely the reason for the variable fat
concentrations. Even though CP values for ingredients
used in the present study were lower than those reported by Murray et al. (1997) and Clapper et al. (2001),
TEAA concentrations were similar. Overall, poultry byproduct meal and chicken-by product meal had higher
CP and total amino acid (TAA) concentrations than
spray-dried cooked chicken and spray-dried egg, which
is likely due to the connective tissue content of the byproduct meals. Chicken by-product meal and poultry
by-product meal were included in the present study as
they are typically used in pet food manufacturing for
their nutrient content and palatability (Heinicke,
2003).
For the blood protein sources tested (Table 4), DM
concentrations were greatest for processed red blood
cells and spray-dried whole beef blood (average = 96.8%)
and least for spray-dried plasma (93.2%). Organic matter, CP, and GE concentrations were least for spraydried plasma, whereas fat concentration was greatest.
For processed red blood cells, the TAA concentration
was much lower than the CP concentration, whereas
for spray-dried plasma, the TAA value was nearly three
percentage units higher. The variation in AA concentrations between spray-dried plasma and processed red
blood cells compared with spray-dried whole beef blood
could be a result of not correcting the values for incomplete recovery during hydrolyis.
Spray-dried blood meals from bovine and porcine
sources vary little in chemical composition (Kats et al.,
1994; DeRouchey et al., 2002), with average DM and
CP concentrations of approximately 92 and 89%, respectively. These values are lower than those noted in the
present study for processed red blood cells and spraydried whole beef blood. The chemical composition of
processed red blood cells in the present study and spraydried blood cells (DeRouchey et al., 2002) are similar.
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Dust et al.
Table 3. Chemical composition of chicken protein sourcesa
Item
CBM
PBM
DM, %
94.9
97.8
SDCC
SDCCL
SDE
97.7
98.3
95.9
DM basis
OM, %
CP, %
Acid-hydrolyzed fat, %
GE, kcal/g
88.2
62.8
18.3
5.5
86.7
64.1
19.6
5.5
94.2
49.2
49.5
7.2
93.2
69.0
22.7
6.0
94.0
52.7
36.9
6.7
Amino acids, %
Essential
Arginine
Histidine
Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Threonine
Tryptophan
Valine
TEAAb
TNEAAc
TAAd
4.81
1.37
2.42
4.49
4.06
1.35
2.54
2.37
0.48
3.16
27.1
38.7
65.8
4.44
1.39
2.39
4.54
4.11
1.33
2.45
2.33
0.55
3.15
26.7
36.1
62.8
2.84
1.32
1.96
3.41
3.65
1.06
1.75
1.61
0.42
2.28
20.3
21.6
41.8
4.00
1.72
2.82
5.72
4.73
1.58
3.06
2.72
0.90
3.87
31.1
29.6
60.7
3.13
1.39
3.10
4.85
3.77
1.76
2.91
2.16
0.83
3.64
27.5
24.8
52.4
a
CBM = chicken by-product meal; PBM = poultry by-product meal; SDCC = spray-dried cooked chicken;
SDCCL = spray-dried cooked chicken liver; SDE = spray-dried egg product.
b
TEAA = total essential amino acids.
c
TNEAA = total nonessential amino acids.
d
TAA = total amino acids.
Kerr et al. (1998) reported that spray-dried plasma had
CP and TEAA concentrations of 82.9 and 39.5%, respectively, values that are similar to ours. A concern with
including blood products is that few palatability studies
using blood meal have been tested in canine diets; however, blood meals have been shown to be unpalatable
Table 4. Chemical composition of blood protein sourcesa
Table 5. Chemical composition of enzyme-hydrolyzed
fish protein concentrate (EHFPC), soybean meal (SBM),
and spray-dried pork liver (SDPL)
Item
PRBC
DM, %
96.6
SDP
SDWBB
93.2
96.9
DM basis
OM, %
CP, %
Acid-hydrolyzed fat, %
GE, kcal/g
92.8
95.3
1.6
5.4
90.9
84.4
2.9
5.1
94.8
95.5
2.1
5.5
Amino acids, %
Essential
Arginine
Histidine
Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Threonine
Tryptophan
Valine
TEAAb
TNEAAc
TAAd
3.60
5.90
0.30
13.47
6.25
0.62
6.42
2.63
0.39
8.87
48.5
39.0
87.5
4.90
2.83
3.01
8.39
7.52
0.71
4.83
4.53
1.40
5.64
43.8
43.4
87.2
3.62
5.92
0.39
13.32
9.23
1.19
6.95
4.20
1.45
8.44
54.8
40.0
94.8
a
PRBC = processed red blood cells; SDP = spray-dried plasma;
SDWBB = spray-dried whole beef blood.
b
TEAA = total essential amino acids.
c
TNEAA = total nonessential amino acids.
d
TAA = total amino acids.
Item
EHFPC
SBM
SDPL
DM, %
94.7
94.4
96.1
OM, %
CP, %
Acid-hydrolyzed fat, %
GE, kcal/g
90.4
62.3
27.3
6.1
92.6
51.0
4.5
4.7
89.9
69.7
14.5
5.5
Amino acids, %
Essential
Arginine
Histidine
Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Threonine
Tryptophan
Valine
TEAAa
TNEAAb
TAAc
2.92
1.23
2.46
3.97
3.99
1.26
2.10
2.08
0.49
3.18
23.7
30.4
54.1
3.60
1.36
2.45
4.07
3.16
0.73
2.56
1.78
0.63
2.64
23.0
26.7
49.7
3.61
1.72
2.81
6.06
4.76
1.51
3.30
2.75
0.80
4.05
31.4
31.7
63.1
DM basis
a
TEAA = total essential amino acids.
TNEAA = total nonessential amino acids.
TAA = total amino acids.
b
c
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Alternative protein sources for dogs
Table 6. Protein quality evaluation of chicken and blood
protein sources and enzyme-hydrolyzed fish protein concentrate, soybean meal, and spray-dried pork livera
Item
b
CBM
PBM
SDCC
SDCCL
SDE
PRBC
SDP
SDWBB
EHFPC
SBM
SDPL
PSI,
protein %c
IDEA
valued
Lysine
digestibility, %e
37.5
26.6
44.4
24.2
81.2
23.9
92.9
92.5
53.4
66.8
26.4
0.54
0.43
0.64
0.47
NDf
0.54
0.58
0.45
ND
0.79
0.48
84.8
68.3
92.5
76.1
ND
84.4
88.4
72.2
ND
88.6
77.4
a
Samples were analyzed in duplicate, but multiples of the same
type of sample, which would allow for statistical analysis, were not
analyzed.
b
CBM = chicken by-product meal; PBM = poultry by-product meal;
SDCC = spray-dried cooked chicken; SDCCL = spray-dried cooked
chicken liver; SDE = spray-dried egg; PRBC = processed red blood
cells; SDP = spray-dried plasma; SDWBB = spray-dried whole beef
blood; EHFPC = enzyme-hydrolyzed fish protein concentrate; SBM =
soybean meal; SDPL = spray-dried pork liver.
c
Protein solubility index of protein in sample based on potassium
hydroxide assay.
d
IDEA = immobilized digestive enzyme assay value used to calculate lysine digestibility.
e
Lysine digestibility value based on IDEA value.
f
ND = no data; IDEA assay not developed for this protein source.
to pigs (Hansen et al., 1993), and this would affect the
inclusion level allowed in a diet.
Enzyme-hydrolyzed fish protein concentrate had concentrations of TAA (Table 5) lower than the CP concentration, indicating the presence of N-containing compounds that are not true protein. Fish proteins are
known to be highly palatable to dogs (Heinicke, 2003).
Soybean meal had higher TNEAA concentrations than
TEAA concentrations. The concentration of TAA is
lower than the CP concentration. The CP value for SBM
used in this study was slightly less than that reported
by Clapper et al. (2001) of 56.6%; however, similar
TEAA concentrations were found in both studies. Soybean protein is typically added to pet foods as a complementary protein in primarily grain-based diets (Hill,
2003). Spray-dried pork liver had higher TNEAA concentrations than TEAA concentrations. Again, the concentration of TAA was lower than the CP concentration.
Liver improves palatability when incorporated as 3%
of the total diet or 5% of the total protein in a diet
(Heinicke, 2003). The addition of liver to a pet food
above a concentration of 10% needs to be closely monitored as the resulting diet may contain excessive vitamin A concentrations (Heinicke, 2003).
Protein quality evaluations of the 11 protein sources
studied are reported in Table 6. Protein solubility index
values differed among chicken protein sources, blood
protein sources, enzyme-hydrolyzed fish protein concentrate, and spray-dried pork liver. There also was
large variation in PSI values within chicken protein and
Table 7. Chick protein efficiency ratio (PER) assay results
Treatmenta
CBM
PBM
SDCC
SDCCL
SDE
PRBC
SDP
SDWBB
EHFPC
SBM
SDPL
SEMb
LSD
Weight
gain,
g/(chickⴢd)
Feed
intake,
g/(chickⴢd)
Protein
intake,
g/(chickⴢd)
PER
6.8
5.2
8.6
12.3
14.0
−1.3
1.1
−1.4
4.6
9.2
10.4
3.4
9.7
19.9
19.3
21.3
27.3
26.3
6.0
10.1
5.0
16.1
24.0
25.9
7.5
21.8
2.0
1.9
2.1
2.7
2.6
0.6
1.0
0.5
1.6
2.4
2.6
0.7
2.1
3.42
2.73
4.06
4.50
5.32
−2.25
1.15
−2.99
2.83
3.84
4.00
0.17
0.49
a
CBM = chicken by-product meal; PBM = poultry by-product meal;
SDCC = spray-dried cooked chicken; SDCCL = spray-dried cooked
chicken liver; SDE = spray-dried egg product; PRBC = processed red
blood cells; SDP = spray-dried plasma; SDWBB = spray-dried whole
beef blood; EHFPC = enzyme-hydrolyzed fish protein concentrate;
SBM = soybean meal; SDPL = spray-dried pork liver.
b
Pooled SEM, n = 10 chicks per treatment.
blood protein sources. Spray-dried plasma and spraydried whole beef blood had PSI values higher than
spray-dried egg. Egg is very close to being an ideal
protein as it has a 95% biological value (FAO, 1970);
therefore, it is a standard for comparison among protein
sources. Enzyme-hydrolyzed fish protein concentrate,
processed red blood cells, SBM, and spray-dried pork
liver had lower PSI values than did spray-dried egg.
The IDEA lysine digestibilities varied among chicken
protein sources, blood protein sources, SBM, and spraydried pork liver, with the largest variation occurring
for the chicken protein sources. The IDEA lysine digestibility was similar for spray-dried cooked chicken liver
and spray-dried pork liver (average = 76.8%), for
chicken-by-product meal and processed red blood cells
(average = 84.6%), and for SBM and spray-dried plasma
(average = 88.5%). Thus, in the protein quality evaluations there was not a clear picture defined as to the
best-quality protein source. Further research into the
appropriate in vitro method for assaying the protein
quality of these products would benefit animal nutrition.
The PER experiment (Table 7) indicated that chicken
protein sources are high-quality proteins as the PER
values were all greater than 2.7. Casein is considered
to be a standard reference protein with a PER value of
2.5 (Munro and Allison, 1969). The highest PER value
was for spray-dried egg, comparable to results of Johnson and Parsons (1997), who reported a PER value for
this ingredient of 4.65. Spray-dried cooked chicken and
spray-dried cooked chicken liver were not different in
PER. Chicken by-product meal had a higher (P < 0.05)
PER value than poultry by-product meal, which was
likely the result of chicken-by product meal being
ground, clean, rendered carcass parts of chicken with
2420
Dust et al.
only trace amounts of feathers and blood, whereas poultry by-product meal is ground, clean, rendered carcass
parts of poultry, but it includes heads, feet, viscera, and
trace amounts of feathers and blood (AAFCO, 2003).
The varying concentrations of poultry parts, especially
feathers, in poultry by-product meal have been reported
to have a negative effect on nutrient digestibilities
(Morris and Balloun, 1973; Latshaw, 1990). Johnson
and Parsons (1997) found poultry by-product meal had
a PER value ranging from 2.43 to 2.50, depending on
ash content.
Feeding the blood protein sources resulted in lower
PER values than the chicken protein sources. Of the
three sources, spray-dried plasma had the highest PER
value. Processed red blood cells and SWBB resulted in
negative PER values, likely due to low feed (and protein) intakes. These diets obviously were unpalatable
to the chicks (Waibel et al., 1977), and other reports
have shown blood products to be unpalatable to pigs
(Kratzer and Green, 1957; Pond and Maner, 1984). The
blood products had low isoleucine concentrations; therefore, the diets may have been deficient in isoleucine,
limiting the growth potential of the chicks. Blood products typically have a favorable profile but have low
concentrations of methionine and isoleucine (Quigley
et al., 2000). Practically speaking, this is of little importance as blood products are added to diets at low concentrations normally, mainly for their immune-enhancing
properties for dogs and pigs (C. M. Grieshop, unpublished data, Univ. of Illinois at Urbana-Champaign;
Coffey and Cromwell, 2001). Nutrient digestibilities
may be affected by spray-dried plasma supplementation as Dust et al. (2003) reported that dogs fed diets
supplemented with 0.5 or 1% spray-dried plasma had
increased (P < 0.05) ileal digestibilities of DM, OM, CP,
and acid-hydrolyzed fat; however, spray-dried plasma
supplementation did not affect total-tract nutrient digestibilities.
Of the other protein sources studied, spray-dried pork
liver resulted in the greatest PER value, followed by
SBM and enzyme-hydrolyzed fish protein concentrate.
The PER value for SBM corroborates the fact that soybean protein inclusion in dog diets results in excellent
CP digestibilities at the ileum (79.2 and 85.3%; Bednar
et al., 2000; Clapper et al., 2001, respectively).
The composition of the processed red blood cells used
in palatability and digestibility studies are presented
in Table 8. Processed red blood cells replaced the corn
gluten meal component of the control diet such that the
treatment diet contained 3% supplemental processed
red blood cells. Diets had similar concentrations of DM,
OM, and GE. For the processed red blood cells-containing diet, CP concentration was 6% greater and acidhydrolyzed fat content 6.5% greater than that of the
control diet.
Palatability results are presented in Table 9. Dogs
consumed more of the control diet than the diet containing 3% processed red blood cells. According to
Griffen (2003), an animal’s appetite can skew food pref-
Table 8. Chemical composition of processed red blood
cells (PRBC) and dietary treatments containing 0 or 3%
PRBC for palatability and digestibility experiments
with dogs
Dietary
treatment
Item
PRBC
0% PRBC
3% PRBC
DM, %
96.1
91.2
91.4
OM, %
CP, %
Acid-hydrolyzed fat, %
GE, kcal/g
90.8
97.2
0.9
5.4
DM basis
94.6
24.9
8.7
4.7
94.0
26.5
9.3
4.8
erence; therefore, consumption alone should not be the
deciding factor regarding food preference. If the dog is
hungry, it could eat equal amounts of both diets. In this
experiment, there was little difference between first
approach of the 3% processed red blood cells diet (51%)
and the 0% processed red blood cells diet (49%). The
dogs first choice for consumption was the control diet
(72%) rather than the 3% processed red blood cells diet
(28%). First approach and first consumed reponses are
very subjective and therefore are not the best indicators
of palatability. In addition, first approach and first consumption data often are difficult to measure and the
repeatability of these measures is questionable
(Griffen, 2003).
The intake ratio for the 3% processed red blood cells
treatment was 0.34. An intake ratio of greater than
0.50 implies a preference for a particular diet. Determination of the corrected intake ratio allowed for statistical evaluation of diet preference if different from zero.
Corrected intake ratio data support the intake ratio
data as the dogs preferred the control diet. Intake ratios
are the best indicators of overall palatability preference
(Trivedi et al., 2000). Based on this intake ratio and
the measures discussed above, it can be concluded that
the 3% processed red blood cells diet was not preferred
Table 9. Palatability results obtained when feeding processed red blood cells (PRBC) to dogs (n = 20)
Dietary
treatment
Item
0%
PRBC
3%
PRBC
SEM
P-value
Amount consumed
(as-fed basis), g/d
Intake ratioa
Corrected intake ratiob
146
0.66
0.16
72
0.34
−0.16
12.8
0.06
0.06
0.01
0.01
0.01
a
Intake ratio = g of 0 or 3% PRBC-containing diet consumed/g of
both diets consumed.
b
Corrected intake ratio = Intake ratio − 0.5, to indicate a diet
preference if there was a diet preference significantly different from
zero.
2421
Alternative protein sources for dogs
Table 10. Nutrient intakes, apparent total tract digestibilities, and fecal characteristics of dogs fed either 0 or 3%
processed red blood cell (PRBC)-containing dietsa
Dietary
treatment
Item
Daily nutrient intake
DM, g
0%
PRBC
3%
PRBC
SEMb
P-valuec
285.5
286.1
21.5
0.97
289.6
27.3
75.0
1,345.7
288.0
28.1
76.8
1,349.0
21.8
2.1
5.7
101.5
0.93
0.67
0.71
0.97
83.2
86.4
90.8
83.0
85.4
82.2
85.4
91.1
80.5
84.4
0.6
0.6
0.3
0.7
0.6
0.22
0.12
0.27
0.01
0.11
182
2.8
195
3.0
15.5
0.1
0.41
0.12
DM basis
OM, g
Acid-hydrolyzed fat, g
CP, g
GE, kcal/kg
Total-tract digestibility, %
DM
OM
Acid-hydrolyzed fat
CP
GE
Fecal characteristics
Fecal output, g/d (as-is basis)
Fecal scorec
a
Values are means, n = 14 per treatment.
SEM = pooled standard error of the mean.
Fecal samples were scored according to the following system: 1 =
hard, dry pellets – small, hard mass; 2 = hard, formed, dry stool –
remains firm and soft; 3 = soft, formed moist – softer stool that retains
shape; 4 = soft, unformed – stool assumes shape of container; 5 =
watery – liquid that can be poured.
b
c
when dogs were offered a choice of a diet containing no
processed red blood cells.
Palatability results can be influenced by several factors, especially flavor, food texture, and size and shape
of kibble (Trivedi et al., 2000). An animal that is accustomed to a certain flavor will prefer to consume a diet
of similar flavor. The processed red blood cells could
have provided a taste that the dogs did not prefer,
thereby lowering the intake ratio. Hansen et al. (1993)
reported that pigs did not find spray-dried blood meal
to be palatable when initially enountered. In our study,
the processed red blood cells had been processed to
remove the color and odor of spray-dried blood meal,
but there must have been other components that led
the dogs to consume more of the 0% processed red blood
cells diet than the 3% processed red blood cells diet.
Nutrient intake, apparent total-tract digestibility,
and fecal characteristic data are presented in Table
10. Intakes were determined during the fecal collection
period. The dogs fed the 0 or 3% processed red blood cells
diets consumed similar quantities of nutrients daily.
Total-tract digestibilities of DM, OM, acid-hydrolyzed fat, and GE did not differ between treatments.
Crude protein digestibility was slightly greater (P =
0.01) for dogs consuming the control diet than for dogs
consuming the 3% processed red blood cells diet. Totaltract CP digestibility values are affected by endogenous
secretions (sloughing of intestinal mucosa, endogenous
proteins, intestinal bacteria, and spent enzymes) and
by ingredient and/or diet processing. The results of the
IDEA and PSI values indicated that processed red blood
cells are a high-quality protein; however, the processed
red blood cells were incorporated into the diet before
extrusion and the protein quality could have been compromised by the conditions of the extrusion process. In
addition, Waibel et al. (1977) suggested that decreased
N digestibility may be due to cross linkages other than
lysine-isopeptides.
Fecal wet weight (as-is basis) and fecal score data
are presented in Table 10. There were no differences
in these response criteria between treatments. Fecal
scores of 3 are considered ideal. Dogs in this study had
close to ideal fecal scores, indicating that feeding a diet
containing processed red blood cells does not alter fecal
characteristics in a negative manner.
Alternative protein sources can serve many functions, including provision of essential and nonessential
AA to the animal, as palatants, or as immune enhancers. Chicken products, particularly eggs, are a good
source of protein and also are highly palatable to dogs
(Heinicke, 2003). Blood products have been shown to
provide immunological enhancement, particularly use
of spray-dried plasma in weanling pig (Coffey and
Cromwell, 2001) and senior dog diets (our unpublished
data). The immunoglobulin fraction in spray-dried
plasma allows the pig to fight against pathogens (Coffey
and Cromwell, 2001). Alternative protein sources are
also good palatants for dog diets, particularly fish and
liver protein sources (Heinicke, 2003). Compositional
protein quality, palatability, and digestibility data are
needed to make optimal use of the many traditional
and alternative protein sources available to the pet
food industry.
Results of the current study indicate that based on
chemical composition and protein quality data, alternative protein sources differ greatly, even within category
of ingredients. The variation in protein quality assessment using the PSI, IDEA, and PER assays indicates
that different fractions of protein quality may be able
to be evaluated. Results of this study indicate that
chicken, enzyme-hydrolyzed fish protein concentrate,
spray-dried pork liver, and soybean meal protein
sources have high protein quality based on the PSI,
IDEA, and PER data. Nonetheless, the blood protein
sources are high-quality proteins based on PSI and
IDEA data but, according to the PER data, have low
protein quality. In addition, blood sources suffer from
poor palatability, even at low-level dietary additions.
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