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4355
© 2012 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2012.90:4355–4361
doi:10.2527/jas2012-5333
Key words: canine, cholesterol , transit time, triglycerides
ABSTRACT: Chews are an important part of the
pet product industry, with many having potential to
decrease plaque or calculus formation. However,
their digestion characteristics and gut transit time are
virtually unknown. Two experiments were conducted
to determine in vitro DM digestibility of expanded pork
skin chews and rawhide chews, and apparent total tract
digestibility (ATTD), gastrointestinal transit time, and
blood metabolite measurements in healthy adult dogs fed
a weight-control commercial diet and expanded pork skin
chews. In Exp.1, an in vitro method that simulated gastric
and small intestinal digestion was used to determine DM
digestibility of expanded pork skin chews and rawhide
chews. In Exp. 2, after a 22-d baseline phase, 10 purpose-
bred, intact female dogs (5 to 5.5 yr of age; 18.9 to 23.1 kg
BW) were fed the diet plus an expanded pork skin chew
(~45 g) each day for 22 d. In vitro gastric digestibility
of expanded pork skin chews increased with time, with
chews being 54.7%, 58.6%, 76.4%, and 86.4% digestible
after 6, 12, 18, and 24 h of gastric digestion, respectively.
By contrast, gastric digestibility of rawhide chews was
7.6% at 6 h, slowly increased over time, and reached a
maximum of 41.6% at 18 h. In vitro gastric plus small
intestinal digestibility results indicated near complete
digestibility of expanded pork skin chews at all times,
whereas rawhide chews were 50 to 85% digestible.
In vivo ATTD of DM, OM, and N were greater (P <
0.05) when dogs were fed expanded pork skin chews
along with the basal diet, compared with the basal diet
alone. However, chew intake did not change transit time
measured with a wireless motility device. By contrast,
motility index and contraction pattern of the colon were
altered (P < 0.05) during chew feeding relative to control.
Blood urea N concentrations were greater (P < 0.05)
in dogs fed expanded pork skin chews, compared with
baseline; this was not surprising, given the increased N
intake and absorption from the chews. Intake of expanded
pork skin chews resulted in reduced blood cholesterol
concentrations (P < 0.05) and tended to decrease blood
triglyceride concentrations (P < 0.10). Expanded pork
skin had a greater DM digestibility than rawhide chews. In
addition, expanded pork skin decreased blood cholesterol
and triglyceride concentrations, which may justify further
research in this area.
In vitro digestibility of expanded pork skin and rawhide chews, and digestion and
metabolic characteristics of expanded pork skin chews in healthy adult dogs
1
S. Hooda,* L. G. Ferreira,* M. A. Latour,† L. L. Bauer,* G. C. Fahey, Jr.,* and K. S. Swanson*
2
*Department of Animal Sciences, University of Illinois, Urbana 61801; and †Department of Animal Sciences, Purdue
University, West Lafayette, IN 47907
INTRODUCTION
Treats are an important contributor to the U.S.
pet product industry, with $2.1 billion in annual sales.
Natural chews are promoted to improve oral health in
pets because chewing helps reduce plaque (Hennet, et
al., 2006) and calculus formation (Hennet et al., 2006;
Stookey, 2009). Production of beef-derived rawhides
and pork skins, which are made from collagenous hy-
podermic interstitial tissue (Bowes et al., 1955), starts
with the washing and cleaning of dried skin. The moist
skin is then cut to size, pressed, shaped, and dried (typi-
cally 65 to 85°C for 24 to 48 h). Rawhide and pork skin
chews are made of collagen, but differences in process-
ing (i.e., expansion technology in expanded pork skin
chews) may impact digestibility. The effects of rawhide
and pork skin chews on gut transit time and nutrient di-
gestibility are largely unknown.
A wireless motility device that is indigestible and
measures gastrointestinal pH, pressure, and temperature
in real time, and transmits this information to a receiver
can be used to calculate transit time. In addition to whole
gut transit time (WGTT), the device will provide gastric
1
Supported by Scott Pet, Inc., Rockville, IN.
2
Corresponding author: ksswanso@illinois.edu
Received March 28, 2012.
Accepted September 16, 2012.
Published January 20, 2015
Hooda et al.
4356
emptying time (GET), small bowel transit time (SBTT),
small and large bowel transit time (SLBTT), and colon
transit time (CTT). Data from such a device are compa-
rable to data from standard measurement methods, such
as scintigraphy (Cassilly et al., 2008; Boillat et al., 2010a).
This technology has been used to diagnose gut motility dis-
orders (Kuo et al., 2008; Rao et al., 2009) in human nutri-
tional studies (Timm et al., 2011; Willis et al., 2011) and is
as repeatable as scintigraphy in dogs (Boillat et al., 2010a).
An in vitro experiment was conducted to determine
the DM digestibility of expanded pork skin and rawhide
chews. A second experiment was conducted to test the ef-
fects of expanded pork skin chews on apparent total tract
digestibility (ATTD), gastrointestinal transit time, and
blood metabolite concentrations in healthy adult dogs.
MATERIALS AND METHODS
All animal procedures were approved by the Universi-
ty of Illinois Institutional Animal Care and Use Committee.
In vitro Digestibility Experiment
In vitro DM digestibility was analyzed using the
modifi ed method of Boisen and Eggum (1991), which
was developed to be similar to in vivo digestibility data
of nonruminants. Briefl y, 250 mL of phosphate buf-
fer and 100 mL of HCl-pepsin solution was added to
containers with whole expanded pork skin and rawhide
chews. After addition of 5 mL of chloramphenicol solu-
tion, containers were sealed and incubated at 39°C for 6,
12, 18, and 24 h for gastric digestibility. Then, samples
were fi ltered through polyester fabric, rinsed, and dried
at 57°C. Small intestinal digestibility was estimated
after further addition of a pancreatin-phosphate buffer
mixture with incubation at 39°C for 18 h.
Animals and Diets
Ten purpose-bred, intact female healthy dogs (5 to
5.5 y of age; 18.9 to 23.1 kg BW; Butler Farms, Clyde,
NY) with hound bloodlines were used in the in vivo
study. Dogs were individually housed (2.3- × 1.1-m pens)
in climate-controlled rooms (Edward R. Madigan Labo-
ratory, University of Illinois, Urbana). Pens allowed for
nose-to-nose contact between dogs in adjacent runs and
visual contact with all dogs in the room. A 16-h light:8-h
dark cycle was used. All dogs were fed a commercially
available dry dog food (Iams Weight Control; Procter
& Gamble, Cincinnati, OH) to maintain BW throughout
the study. The commercial dog food was formulated to
meet all nutrient requirements of adult dogs (AAFCO,
2009). Food intake was recorded daily. Fresh water was
offered for ad libitum consumption.
Experimental Design
After a 22-d baseline phase, during which only the dry
commercial diet was fed, diet plus an expanded pork skin
chew (45 to 55 g) was fed each day during a 22-d treat-
ment period. On d 8 to 11 of the baseline and treatment
periods, total fecal collection was conducted to determine
ATTD. A wireless motility device (SmartPill Corp., Buf-
falo, NY) was used to determine gut motility outcomes
during the last 10 d (d 12 to 21; 2 dogs measured each
day) of each period. A 24-h food-restricted blood sample
was collected on the last day (d 22) of the baseline and
treatment phases for serum chemistry measurements.
Fecal and Blood Sample Collections
During the 4-d fecal collection phase, total feces
excreted were collected from the bottom of the cage,
weighed, scored, and frozen at –20ºC until further
analyses. The fecal samples were scored according to
the following system: 1 = hard, dry pellets, which are
small hard mass; 2 = hard, formed and dry stool, which
remains fi rm and soft; 3 = soft, formed and moist stool,
which retains shape; 4 = soft, unformed stool, which as-
sumes shape of container; and 5 = watery, liquid, which
can be poured. A fresh fecal sample (within 15 min after
defecation) was used to determine pH (AP10 pH Meter;
Denver Instrument, Bohemia, NY). This instrument was
equipped with an electrode (Beckman Instruments, Inc.,
Fullerton, CA). On blood sampling days, 5 mL of blood
was collected for serum metabolite measurements via
jugular puncture. Samples were immediately transferred
to appropriate Vacutainer tubes (Becton Dickinson,
Franklin Lakes, NJ), allowed to clot for at least 30 min,
and then centrifuged (2,000 × g for 15 min at 4
o
C) for
serum collection. Serum samples were analyzed at the
University of Illinois Veterinary Medicine Diagnostics
Laboratory, using a clinical chemistry analyzer (Roche-
Hitachi 911; Roche Diagnostics, Indianapolis, IN).
Chemical Analyses
Diet and fecal samples were ground through a 2-mm
screen in a Wiley Mill (Model 4, Thomas Scientifi c,
Swedesboro, NJ) and then analyzed according to pro-
cedures for DM and OM composition (Methods 934.01,
942.05; AOAC, 2006). Total N was analyzed using Leco
technology (Method 992.15; AOAC, 2006). Total lipid
content (acid hydrolyzed fat) of the diets and feces were
determined according to the methods of AACC (1983)
and Budde (1952). Gross energy of diet samples was
measured using an oxygen bomb calorimeter (Model
1261; Parr Instruments, Moline, IL).
Digestion characteristics of chews in dogs
4357
Gut Motility Analysis
Gut motility analysis was conducted, again, using a
wireless motility technology (SmartPill Corp.), accord-
ing to manufacturer instructions. Briefl y, the process
included: 1) just before use, the capsule (27 × 12 mm)
was activated using a strong magnet; 2) the capsule was
given orally to dogs after they fi nished eating their food;
3) once the capsule had entered the stomach (indicated
by decrease in pH to <3 on data receiver display), the
data receiver was placed on the cage of the dog; 4) pH,
temperature, and pressure data were transmitted to the
receiver during transit; 5) once the capsule was passed in
the feces, the data were transferred from the data receiv-
er to the computer. SmartPill software was used to cal-
culate gut transit and motility characteristics. All gastric
emptying and transit times (GET, SBTT, CTT, SLBTT,
and WGTT) were calculated on the basis of pH data.
The GET is calculated as time between capsule inges-
tion (indicated by temperature increase) and an abrupt
rise in pH from the low pH of the stomach to an alkaline
duodenal pH. The SBTT is the time between duodenal
and cecum entry. Cecal entry is the time when the fi rst
sustained drop in pH of more than 1 unit is noticed. The
CTT is the difference between entry into the cecum and
body exit (indicated by abrupt temperature decrease).
The SLBTT is the sum of SBTT and CTT. The WGTT is
the time between wireless motility device ingestion and
exit from the body.
Statistical Analysis
Data for continuous variables were analyzed with the
MIXED procedure and data for discontinuous variables
were analyzed with the GLIMMIX procedure (SAS Inst.
Inc., Cary, NC), using dog as an experimental unit. The
statistical model included fi xed effects of diet. Results
were reported as least squares means with P < 0.05 de-
fi ned as signifi cant and P ≥ 0.05 and < 0.10 as trends.
RESULTS
In vitro Digestibility
In vitro gastric digestibility of expanded pork skin
chews was 54.7%, 58.6%, 76.4%, and 86.4%, after 6,
12, 18, and 24 h, respectively (Table 1). By contrast,
gastric digestibility for rawhide chews was 7.6% at 6
h and reached a maximum of 41.6% at 18 h. In vitro
gastric + small intestinal digestion results indicated near
complete digestibility of expanded pork skin chews at
all times (Table 2). Rawhide chews were only 70% di-
gested after 6 h gastric + 18 h small intestinal digestion.
Gastric digestion at 12 and 18 h did not result in further
improvement in rawhide digestibility. At 24 h gastric +
18 h small intestinal digestion of rawhide chews, DM
digestibility increased to 85%.
Food Intake, Fecal Output, Fecal pH, and Fecal Score
All dogs remained healthy throughout the experi-
ment. Two dogs refused to eat chews consistently and
were removed from the study. Nutrient composition of
the control diet and chews is presented in Table 3. Or-
ganic matter content was slightly greater and ash con-
tent was less in expanded pork skin chews than the basal
diet. The nitrogen content was greater (16.1%) in ex-
panded pork skin chews. By contrast, acid hydrolyzed
fat content was less in expanded pork skin chews than
Table 1. In vitro gastric (HCl/pepsin) digestibility results
for expanded pork skin and rawhide chews (n = 2 or 3)
Item
Expanded pork
skin chews
Rawhide chews
6 h, gastric digestion
Initial DM weight, g 47.26 69.24
Final DM weight, g 21.55 64.04
DM digestibility, % 54.7 7.6
12 h, gastric digestion
Initial DM weight, g 48.43 59.88
Final DM weight, g 20.72 48.68
DM digestibility, % 58.6 19.1
18 h, gastric digestion
Initial DM weight, g 42.01 63.21
Final DM weight, g 9.89 37.62
DM digestibility, % 76.4 41.6
24 h, gastric digestion
Initial DM weight, g 37.35 67.85
Final DM weight, g 5.10 52.12
DM digestibility, % 86.4 23.1
Table 2. In vitro gastric and small intestinal digestibility re-
sults for expanded pork skin and rawhide chews (n = 2 or 3)
Item Expanded pork skin chews Rawhide chews
6 h gastric + 18 h small intestinal digestion
Initial DM weight, g 46.09 53.04
Final DM weight, g 0.43 16.27
DM digestibility, % 99.0 70.1
12 h gastric + 18 h small intestinal digestion
Initial DM weight, g 45.11 52.68
Final DM weight, g 0.00 22.49
DM digestibility, % 100.0 59.3
18 h gastric+ 18 h small intestinal digestion
Initial DM weight, g 38.60 65.91
Final DM weight, g 0.04 32.99
DM digestibility, % 99.9 52.9
24 h gastric + 18 h small intestinal digestion
Initial DM weight, g 40.61 63.93
Final DM weight, g 0.03 9.98
DM digestibility, % 99.9 85.9
Hooda et al.
4358
the control diet. Expanded pork skin chews had greater
GE content than the control diet.
Intake of the control diet alone tended to be greater
(P = 0.089) during the baseline period (Table 4). How-
ever, total food intake (basal diet + chew) did not change
between baseline and expanded pork skin chew intake
periods. Fecal output (DM basis) tended to be less (P <
0.07) for dogs eating expanded pork skin chews, com-
pared with the control diet alone. Fecal pH and fecal
scores for dogs during the feeding of expanded pork skin
chews were not different from the control diet alone.
Apparent Total Tract Nutrient Digestibility
Apparent total tract DM, OM, and N digestibility
were greater (P < 0.05) for dogs consuming expanded
pork skin chew, compared with the control diet alone
(Table 5). Expanded pork skin chew consumption did
not affect the apparent digestibility of fat and ash.
Transit Time
Transit time outcomes did not differ for dogs fed ex-
panded pork skin chews, compared with the control diet
(Table 6). Similarly, the motility index, contractions per
minute, and pH of stomach, antrum, duodenum, and small
bowel did not differ between dogs fed expanded pork skin
chews and control diet (Table 7). However, the motility
index and number of contractions per minute for the colon
were less (P < 0.05) when dogs were fed expanded pork
skin chews, compared with control diet alone.
Serum Chemistry
All of the serum metabolite concentrations were
within the normal range for adult dogs (Table 8). Blood
urea N concentrations were greater (P < 0.05) for dogs
fed expanded pork skin chews, compared with control
diet alone. By contrast, blood cholesterol concentrations
were less (P < 0.05) for dogs fed chews, as compared
with control diet alone. Blood triglyceride concentra-
tions tended to be less (P = 0.062) after intake of ex-
panded pork skin chews, compared with control diet
alone. No other serum metabolites were affected by ex-
panded pork skin chew consumption.
Table 3. Chemical composition of the commercial
weight-control baseline diet and expanded pork skin
chews fed to healthy adult dogs
Item Control diet Expanded pork skin chews
DM content, % 93.3 91.1
Content, DM basis
OM, % 93.2 96.8
Ash, % 6.8 3.2
N, % 3.6 16.1
Acid hydrolyzed fat, % 10.6 6.7
GE, kcal/kg 4,419 4,781
Table 4. Food intake, fecal output, fecal pH, and fecal
scores in dogs (n = 8) fed a commercial weight-control
diet and diet + expanded pork skin chews
Item Control
Control + expanded
pork skin chews
P-value
Control diet intake 287.5 ± 10.7 260.0 ± 10.7 0.089
(as-fed basis), g/d
Control diet intake 268.3 ± 9.9 242.6 ± 9.9 0.089
(DM basis), g/d
Chew intake 0.0 45.1 ± 3.2 -
(as-fed basis), g/d
Chew intake 0.0 41.0 ± 2.9 -
(DM basis), g/d
Total intake 287.5 ± 11.0 305.0 ± 11.0 0.279
(as-fed basis), g/d
Total intake 268.3 ± 10.3 283.6 ± 10.3 0.308
(DM basis), g/d
Fecal output 152.2 ± 8.0 137.7 ± 8.0 0.208
(as-fed basis), g/d
Fecal output 47.9 ± 1.5 43.6 ± 1.5 0.067
(DM basis), g/d
Fecal pH 6.4 ± 0.2 6.1 ± 0.2 0.285
Fecal score
1
2.6 ± 0.1 2.6 ± 0.1 0.605
1
Fecal score based on the following scale: 1 = hard, dry pellets; 2 = dry,
well-formed stool; 3 = soft, moist, formed stool; 4 = soft, unformed stool; 5 =
watery, liquid that can be poured.
Table 5. Apparent total tract digestibility in dogs (n =
8) fed a commercial weight-control diet and diet + ex-
panded pork skin chews (%)
Item Control
Control + expanded
pork skin chews
P-value
DM 82.1 ± 0.5 84.4 ± 0.5 0.005
OM 85.4 ± 0.4 87.5 ± 0.4 0.003
N 81.8 ± 0.8 88.6 ± 0.8 <0.001
Fat 88.6 ± 0.4 89.5 ± 0.4 0.151
Ash 37.0 ± 1.9 37.6 ± 1.9 0.811
Table 6. Gastrointestinal transit time for dogs (n = 8) fed
a commercial weight-control diet and diet + expanded
pork skin chews
Item
1
Control
Control + expanded
pork skin chews
P-value
GET, min 1,357 ± 223 1,842 ± 238 0.161
SBTT, min 145 ± 14 131 ± 15 0.489
CTT, min 1,076 ± 117 1,145 ± 138 0.707
SLBTT, min 1,226 ± 127 1,284 ± 150 0.772
WGTT, min 2,610 ± 261 3,130 ± 309 0.228
1
GET = gastric emptying time; SBTT = small bowel transit time; CTT =
colon transit time; SLBTT = small and large bowel transit time; and WGTT
= whole gut transit time.
Digestion characteristics of chews in dogs
4359
DISCUSSION
To our knowledge, this is the fi rst study to report in
vitro DM digestibility of whole rawhide vs. expanded
pork skin chews. This study indicated a high gastric and
small intestinal in vitro DM digestibility of expanded
pork skin chews, compared with rawhide chews. Al-
though chews are moistened and chewed by dogs, large
pieces may be consumed. Our digestibility results in-
dicated high values (54.7%, 58.6%, 76.4%, and 86.4%
after 6, 12, 18, and 24 h of gastric digestion and 99 to
100% after gastric + small intestinal digestion) and,
thus, safety of expanded pork skin chews if ingested as
large chunks.
In vitro results on expanded pork skin chews were
supported in the in vivo study that demonstrated a high
digestibility and unaltered gut transit time. The nutrient
digestibility of the control diet + expanded pork skin
chew was compared with that of the control diet alone.
Dry matter, OM, and N digestibilities were greater as a
result of expanded pork skin chew consumption, which
may be interpreted as greater digestibility of chews. In
the current study, a weight-control diet was fed. It is un-
known how nutrient digestibility may have been affect-
ed by expanded pork skin chew consumption if a diet
with greater digestibility had been fed. A previous study
in rats indicated that the digestibility of collagen was
near 100% (Whitemore et al., 1975). This also might be
true in dogs, but collagen digestibility in dogs has not
been assessed. Furthermore, there was no effect on fat
or ash digestibility, indicating that expanded pork skin
chews did not negatively affect ATTD of any nutrients
measured. In the future, it would be informative to com-
pare the nutrient digestibility of pork skin vs. rawhide
chews to determine whether dogs respond similarly to
both products.
Because dog owners sometimes are concerned
about the risk of choking or gastrointestinal blockage
when chews are fed, gut transit time data for dogs fed
expanded pork skin chews was collected and compared
with data obtained with dogs fed the control diet alone.
This is the fi rst study to use wireless motility technol-
ogy in a canine nutritional intervention study. In the
current study, there was a numerical increase in GET
when dogs were fed expanded pork skin chews and the
control diet, as compared with feeding the control diet
alone, but this was due to high variability among dogs
and data were not statistically different. Increased GET
may not be surprising because the meal must be broken
down to small particles in the stomach before passing
into the duodenum. We observed greater GET values
than those reported in the literature (22 to 30 h in the
current study vs. 6.5 to 15.0 h observed in Boillat et al.,
2010a,b), even with dogs of similar BW and use of the
same technology. Gastric emptying may be controlled
and affected by many factors, including diet type (e.g.,
extruded vs. canned), viscosity, or macronutrient com-
position (e.g., fat¸ protein, or carbohydrate), which may
have contributed to differences among studies (Ehrlein
Table 7. Gastrointestinal motility index, contractions/
minute, and pH for dogs (n = 8) fed a commercial
weight-control diet and diet + expanded pork skin chews
Item Control
Control + expanded
pork skin chews
P-value
Motility index
1
Stomach 231.8 ± 70.5 251.1 ± 75.4 0.854
Antrum 198.3 ± 104.0 258.9 ± 111.2 0.697
Duodenum 1,505.5 ± 461.3 876.5 ± 493.2 0.369
Small bowel 1,168.8 ± 229.1 682.1 ± 244.9 0.170
Colon 243.9 ± 23.7 148.0 ± 28.0 0.026
Contractions/min
Stomach 2.1 ± 0.2 1.7 ± 0.2 0.264
Antrum 1.5 ± 0.6 2.5 ± 0.7 0.307
Duodenum 11.2 ± 1.0 11.2 ± 1.1 0.979
Small bowel 14.5 ± 1.0 11.6 ± 1.1 0.070
Colon 1.9 ± 0.2 0.9 ± 0.2 0.006
pH
Stomach 1.3 ± 0.1 1.4 ± 0.1 0.787
Antrum 1.4 ± 0.2 1.4 ± 0.2 0.925
Duodenum 6.8 ± 0.1 7.0 ± 0.2 0.192
Small bowel 7.7 ± 0.1 7.9 ± 0.1 0.371
Colon 6.2 ± 0.3 5.9 ± 0.3 0.469
1
Calculated by software as sum of pressure amplitude × no. contractions +
1. Indication of gastrointestinal motility defi ned by movements of the diges-
tive system and transit of contents within it.
Table 8. Blood metabolite concentrations for dogs (n =
8) fed a commercial weight-control diet and diet + ex-
panded pork skin chews
Item Control
Control + expanded
pork skin chews
P-value
Creatinine, mg/dL 0.8 ± 0.0 0.8 ± 0.0 0.438
Urea nitrogen, mg/dL 9.8 ± 1.3 17.8 ± 1.3 <0.001
Total protein, g/dL 5.7 ± 0.1 5.9 ± 0.1 0.254
Albumin, g/dL 3.2 ± 0.1 3.2 ± 0.1 0.632
Calcium, mg/dL 9.8 ± 0.1 9.6 ± 0.1 0.085
Phosphorus, mg/dL 3.3 ± 0.1 3.3 ± 0.1 0.885
Sodium, mmol/L 145.9 ± 0.5 144.3 ± 0.5 0.051
Potassium, mmol/L 4.1 ± 0.1 4.3 ± 0.1 0.373
Chloride, mmol/L 113.0 ± 0.6 111.4 ± 0.6 0.088
Glucose, mg/dL 83.4 ± 2.2 84.8 ± 2.2 0.659
Alkaline phosphatase, U/L 51.3 ± 4.8 39.5 ± 4.8 0.105
Corticosteroid-induced 5.8 ± 2.1 4.6 ± 2.1 0.626
alkaline phosphatase, U/L
Alanine aminotransferase, U/L 55.1 ± 10.3 49.4 ± 10.3 0.698
Gamma-glutamyl transferase, U/L 4.1 ± 0.3 3.4 ± 0.3 0.109
Total bilirubin, mg/dL 0.2 ± 0.0 0.2 ± 0.0 0.090
Cholesterol, mg/dL 244.8 ± 17.7 175.4 ± 17.7 0.015
Triglycerides, mg/dL 45.8 ± 3.4 35.9 ± 3.4 0.062
Bicarbonate, mmol/L 21.1 ± 0.5 22.4 ± 0.5 0.114
Hooda et al.
4360
and Prove, 1982; Meyer et al., 1985; Clegg and Shafat,
2010). In contrast to the current study, in which dogs
were fed 100% of their daily meal before dosing with
the wireless motility device, dogs in those studies were
fed only 25% and 30% (Boillat et al., 2010a,b) of their
daily food intake, which likely contributed to the differ-
ences. Because none of the mean gastrointestinal transit
times measured in expanded pork skin chews-fed dogs
were altered, compared with the control, our data indi-
cate that addition of pork chews did not adversely affect
gastrointestinal motility. The large size of the wireless
motility pill means that it is retained in the stomach until
the end of the meal. Even though this may not allow an
estimation of initial emptying, it should serve as a valid
method of estimating when the meal was completely
moved from the stomach. Because some dogs should not
be fed highly digestible, high protein-containing foods
(e.g., renal disease patients), feeding must be considered
on a case-by-case basis. The likelihood of choking was
not tested in this study.
Serum chemistry measurements were also per-
formed to assess the safety of expanded pork skin chew
consumption. Blood urea nitrogen was greater during
expanded pork skin chew consumption, but still within
the reference range (<30 mg/dL), a response that was
likely due to the intake of a highly digestible N source in
the form of a chew. In addition, normal creatinine con-
centrations indicated that expanded pork skin chew con-
sumption for 22 d did not affect kidney function. An in-
teresting observation of this study was the lesser serum
cholesterol and trend toward lesser serum triglyceride
concentrations after expanded pork skin chew consump-
tion. In humans, high protein diets have been promoted
to increase BW loss and improve blood triglyceride con-
centrations in overweight and obese individuals (Papak-
onstantinou et al., 2010; Skov et al., 1999). In the current
study, we observed decreased cholesterol and a tendency
for decreased triglycerides in healthy, lean adult dogs.
These decreases may have been due to altered hepatic
lipid metabolism or increased energy expenditure from
increased protein intake, because ATP is required for the
initial steps of metabolism, storage, and oxidation, in-
cluding urea synthesis. In comparison to the diet alone,
which provided approximately 22%, 25%, and 53% of
ME from protein, fat, and digestible carbohydrates, re-
spectively, the diet + pork skin chews provided approx-
imately 31%, 23.5%, and 45.5% of ME from protein,
fat, and digestible carbohydrates, respectively. More
research is necessary to identify mechanisms by which
these effects may have occurred. Although our dogs had
normal blood triglyceride and cholesterol concentra-
tions, and none were obese, this interesting observation
needs further research in overweight or obese dogs. The
ability to positively affect blood triglyceride and choles-
terol concentrations may be another benefi t to expanded
pork skin chew consumption.
In conclusion, our in vitro results indicated a high
DM digestibility of expanded pork skin chews, com-
pared with rawhide chews. Our in vivo experiment con-
fi rmed the high DM digestibility of expanded pork skin
chews and demonstrated no differences in gastrointes-
tinal transit outcomes. The decreased cholesterol and
trend for decreased blood triglyceride concentrations
observed with expanded pork skin chew consumption
highlights another possible benefi t and justifi es further
research in this area. The feeding of expanded pork skin
chews seemed to be safe because none of the other se-
rum chemistry metabolites, fecal characteristics, and
general behavior of dogs was altered during expanded
pork skin chew feeding.
LITERATURE CITED
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