ArticlePDF Available

Dietary beet pulp decreases taurine status in dogs fed low protein diet

Authors:

Abstract and Figures

Background It is known that large dogs who are fed lamb and rice diets are at increased risk to develop taurine-deficiency-induced dilated cardiomyopathy. Since dogs obligatorily conjugate bile acids (BA) with taurine, we determined whether rice bran (RB) or other fibers (cellulose; CL, beet pulp; BP) would affect BA excretion and/or the taurine status of dogs. Results Eighteen medium/large mixed-breed dogs were given purified diets containing CL, BP, or RB for 12 weeks. Taurine concentrations in plasma and whole blood were significantly decreased at week 12. The BP group, compared to the CL or RB groups, showed significantly lower taurine concentrations in plasma (6.5 ± 0.5 vs 20.4 ± 3.9 and 13.1 ± 2.0 μmol/L, respectively, P < 0.01, mean ± SEM) and in whole blood (79 ± 10 vs 143 ± 14 and 127 ± 14 μmol/L, respectively, P < 0.01), lower apparent protein digestibility (81.9 ± 0.6 vs 88.8 ± 0.6 and 88.1 ± 1.2 %, respectively, P < 0.01), and higher BA excretions (5.6 ± 0.1 vs 3.4 ± 0.5 and 3.4 ± 0.4 μmol/g feces, respectively, P < 0.05) at week 12. Conclusions These results do not support the hypothesis that RB is likely to be a primary cause of lamb meal and rice diets, increasing the risk of taurine deficiency in large dogs. However these indicate that BP may contribute to a decrease taurine status in dogs by increasing excretion of fecal BA and decreasing protein digestibility, thus decreasing the bioavailability of sulfur amino acids, the precursors of taurine.
Content may be subject to copyright.
R E S E A R C H Open Access
Dietary beet pulp decreases taurine status
in dogs fed low protein diet
Kwang Suk Ko
1,2*
and Andrea J. Fascetti
2
Abstract
Background: It is known that large dogs who are fed lamb and rice diets are at increased risk to develop
taurine-deficiency-induced dilated cardiomyopathy. Since dogs obligatorily conjugate bile acids (BA) with taurine,
we determined whether rice bran (RB) or other fibers (cellulose; CL, beet pulp; BP) would affect BA excretion and/or
the taurine status of dogs.
Results: Eighteen medium/large mixed-breed dogs were given purified diets containing CL, BP, or RB for 12 weeks.
Taurine concentrations in plasma and whole blood were significantly decreased at week 12. The BP group, compared
to the CL or RB groups, showed significantly lower taurine concentrations in plasma (6.5 ± 0.5 vs 20.4 ± 3.9 and
13.1 ± 2.0 μmol/L, respectively, P< 0.01, mean ± SEM) and in whole blood (79 ± 10 vs 143 ± 14 and 127 ± 14 μmol/L,
respectively, P< 0.01), lower apparent protein digestibility (81.9 ± 0.6 vs 88.8 ± 0.6 and 88.1 ± 1.2 %, respectively,
P< 0.01), and higher BA excretions (5.6 ± 0.1 vs 3.4 ± 0.5 and 3.4 ± 0.4 μmol/g feces, respectively, P< 0.05) at week 12.
Conclusions: These results do not support the hypothesis that RB is likely to be a primary cause of lamb meal and
rice diets, increasing the risk of taurine deficiency in large dogs. However these indicate that BP may contribute to a
decrease taurine status in dogs by increasing excretion of fecal BA and decreasing protein digestibility, thus decreasing
the bioavailability of sulfur amino acids, the precursors of taurine.
Keywords: Taurine deficiency, Bile acid excretion, Fiber, Dogs, Dilated cardiomyopathy
Background
It is known that dogs, under normal dietary conditions,
synthesize taurine via the activities of two key enzymes,
cysteine dioxygenase and cysteine sulfinic acid decarb-
oxylase [1]. Taurine is synthesized from its precursor
cysteine, resulting in sufficient quantities to meet their
metabolic needs. However in recent years there were
several reports that dogs may develop taurine deficiency-
induced dilated cardiomyopathy (DCM). This has become
more common in large dogs fed certain diets [2] and/or
belonging to certain breeds [3, 4]. The main ingredients in
the dog food fed to the taurine deficient dogs were lamb
meal and rice, including rice bran [5]. Lamb meal has
been reported to have a particularly low bioavailability of
cysteine in dogs [6]. In a study where cats were fed a diet
containing full fat stabilized rice bran, the cats had a lower
blood taurine concentration compared to cats fed the
same diet with cornstarch substituted for the rice bran [7].
Therefore, rice bran, in addition to lamb meal, may play a
role in the development of taurine deficiency in dogs.
Various investigators have reported that the consump-
tion of diets containing full fat rice bran results in redu-
cing cholesterol concentrations in both liver and blood
of several species; eg, in rats [8, 9], hamsters [10], and
humans [11, 12]. One of the possible mechanisms for
this effect is the high fermentability of rice bran, resulting
in enhanced bile acid (BA) excretion and/or degradation
(by increased microflora activity in the gut). According to
the report of Gestel et al. [13], full fat rice bran fed
to rats increased both BA excretion and bacterial activity,
compared to controls fed a starch-based diet. Supporting
evidence for the role of gut microflora in taurine loss has
been reported for other species. Kim et al. [14, 15] re-
ported a significant decrease in fecal cholyltaurine hydro-
lase activity (an enzyme produced by intestinal bacteria),
and total fecal BA excretion with the addition of dietary
* Correspondence: kko@ewha.ac.kr
1
Department of Nutritional Science and Food Management, Collage of
Science & Industry Convergence, Ewha Womans University, 52
Ewhayeodae-gil, Seodaemun-gu, Seoul 120-750, Korea
2
Department of Molecular Biosciences, School of Veterinary Medicine,
University of California Davis, One Shield Ave, Davis, CA 95616, USA
© 2016 The Author(s). Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Ko and Fascetti Journal of Animal Science and Technology (2016) 58:29
DOI 10.1186/s40781-016-0112-6
antibiotics in cats. The administration of antibiotics re-
sulted in the repletion of taurine in taurine-deficient cats
within 3 weeks of treatment. It has been reported that
dogs fed a lamb meal and rice diet showed higher urinary
taurine excretion when antibiotics were added to their diet
[16]. This suggests that highly populated microflora in the
gut interferes with normal entero-hepatic re-utilization of
taurine (taurocholic acid), which in turn prevents the
maintenance of taurine homeostasis and decreases the
quantity of taurine available for other metabolic functions
and for renal excretion.
We postulate that dietary full-fat rice bran binds
BA in the small intestine in dogs and thereby increases
BA excretion, interfering with the entero-hepatic recycling
of taurine-conjugated bile salts and lowering total body
taurine status in dogs.
In the present study, the effects of dietary full fat rice
bran on taurine status and BA excretion in dogs fed a
diet near-limiting in sulfur amino acids were compared
to those of dogs fed beet pulp, another common fiber
source in dog food. Cellulose was used as the control
fiber. Since an excess of dietary sulfur amino acids in
dogs may mask the effects of marginally limiting sulfur
amino acid metabolites such as taurine and glutathione,
dogs were restricted in the amount of protein intake to
2025 % above their minimum maintenance require-
ment described in National Research Council [17].
Methods
Animals and diets
The husbandry and treatments of the animals for the
study were approved by the Animal Use and Care Ad-
ministrative Advisory Committee at the University of
California at Davis and the dogs in this study were taken
care of in compliance with the National Research Coun-
cil [18] guidance for laboratory animals. Eighteen intact
male, mixed-breed dogs (Covance Stock and Broodstock
Colony, Kalamazoo, MI, USA) were used for the study.
Mean body weight (BW) of the 16 years old dogs at
the initiation of the study was 29.1 ± 0.7 Kg (mean ±
SEM). Six animals were assigned to each of the three ex-
perimental groups: cellulose (CL), beet pulp (BP) and
rice bran (RB), based on similar BW of the dogs. The
dogs were housed individually in indoor wire-mesh en-
closures with coated rod-bottom floors at commercial
facilities (Covance Research Products, Kalamazoo, MI,
USA), providing a 12 h dark-light cycle and temperature
control at 1829 °C. Observations for general health and
appearance were done three times a day at the discretion
of the veterinarians and daily monitoring for food con-
sumption was provided throughout the study. Weekly
BW and body condition score (BCS, 9 point scale) were
measured for each dog [19]. Food for all of the dogs for
the study was provided once a day between 7 AM and
9 AM and water was given ad-libitum throughout the
experiment.
Four complete, balanced diets were provided by a
commercial laboratory animal food company (TestDiet®/
LabDiet®, Purina, St. Louis, MI, USA). The ingredients
and chemical compositions of the diets for the study are
shown in Table 1. For the adaptation period, a pre-
feeding (PF) diet, a complete and balanced dry expanded
diet with 29.5 % protein containing 0.58 % methionine
and 0.46 % cyst(e)ine (as-fed basis) was prepared to
maintain an excess production of taurine for the main-
tenance of taurine homeostasis in these dogs. For the ex-
perimental period, three purified diets with the three
different fiber sources, CL, BP and RB, were prepared,
which, by design, included 12 % protein containing
0.23 % methionine and 0.12 % cyst(e)ine (as-fed basis).
This prevented an excess of substrates for taurine
synthesis that might overwhelm the effects of fibers on
taurine metabolism studied. Twelve percent protein is
higher than the minimum requirement of protein for
maintenance of dogs described in National Research
Council [17] and 0.35 % of sulfur amino acid concentra-
tion in the diets is within the range of total sulfur amino
acid requirement (0.20.4 % of diets) for maintenance of
adult dogs as determined by short-term nitrogen balance
experiments [2022]. Ten percent full-fat RB was used for
the RB diet and the amounts of the fibers used in the
other two diets were formulated, by calculation, to have
the same amount of total dietary fiber (TDF) as that in the
RB diet. Chromium oxide (0.02 %) was added to the ex-
perimental diets to use in determining apparent protein
digestibility. The leftover and spilled food was collected
daily and used to calculate food intake of each dog. The
amounts of the food provided were adjusted weekly, based
on changes of BW and BCS to aim toward an ideal BCS
(5 out of 9 on the 9 point scale).
Design and treatments
During the adaptation period the dogs were given the
PF diet for 8 weeks to ensure that they were not taurine
deficient. The last two weeks of the adaptation period
were included for sample collections as week 0, which
was the initiation of the measurements. Then, dogs
were assigned to one of three experimental groups (CL,
BP, or RB group, respectively) to establish similar mean
BW among the experimental groups. During the ex-
perimental period (from week 2 to week 12), the three
different experimental diets were given to the desig-
nated groups. Throughout the experiment, including
the last two weeks of the adaptation period, blood was
collected on the last day of each 2 week-period, urine
was collected biweekly on a day before blood collection,
and feces were collected during the last 5 days of each
2 week-period. Plasma (PL) taurine, whole blood (WB)
Ko and Fascetti Journal of Animal Science and Technology (2016) 58:29 Page 2 of 10
taurine, urine taurine, BA excretion, apparent protein
digestibility, blood thiols and PL complete amino acid
profiles (CAAP) were measured. To assure the health
conditions of the dogs, blood chemistries and complete
blood cell counts were performed on the samples taken
on the last day of the adaptation period (IDEXX Preclin-
ical Research Services, Westbrook, ME, USA) and the
concentrations of total protein and albumin of PL were
done from the PL drawn on the last day of the experimen-
tal periods (Veterinary Medicine Teaching Hospital of the
School of Veterinary Medicine, University of California,
CA, USA).
Sample collections and measurements
Blood (approximately 6 mL) was taken at the end of each
2 week-period to measure taurine, thiols, and amino acids.
Every blood drawing was performed prior to feeding
through cephalic vein by venipuncture using heparinized
syringes (20 μL of sodium heparin solution, 1000 USP
units/mL). Urine for assays of taurine and creatinine con-
centrations was collected, biweekly, for 14 h in an individ-
ual metabolic cage, one day before the blood was collected.
The urine was collected in a container held in ice water.
A portion of WB (approximately 2 mL) was stored fro-
zen (20 °C) for WB taurine assay. Another portion of
WB collected (approximately 4 mL) was immediately
centrifuged (~1,200 × g for 10 min) to obtain PL. An ali-
quot of PL or urine (approximately 0.5 mL) was mixed
with an equal volume of 0.24 mol/L of 5-sulfosalicylic
acid, centrifuged at 15,800 × g for 15 min at 4 °C and the
supernatant was collected. The resulting deproteinized
PL or urine samples were assayed for taurine and for PL
Table 1 Chemical composition and ingredients of the diets for the experiment
b,c
Units PF Diet
a,d
CL Diet
a
BP Diet
a
RB Diet
a
Protein % 29.5 11.8 11.7 11.7
Methionine + Cystine % 1.04 0.35 0.35 0.34
Taurine % 0.04 - - -
Fat % 18.5 20.3 20.3 20.3
Fibers % 2.0
e
2.51
f
1.98
f
2.68
f
Insoluble dietary fibers
f
% - 1.83 1.98 1.81
Soluble dietary fibers
f
% - 0.68 0.00 0.87
Metabolizable Energy
c
kJ/g 15.0 19.2 18.7 17.5
Casein - vitamin free % - 5.00 6.71 3.00
Soy protein isolate % - 7.90 5.62 8.38
Corn starch % - 37.61 35.55 33.76
Sucrose % - 20.00 20.00 20.00
Lard % - 20.18 20.16 18.18
Cellulose powdered
g
% - 2.15 - -
Beet pulpdried
g
% - - 4.70 -
Rice bran full fat
g
% - - - 10.00
Mineral/Vitamin
h
% - 6.84 6.94 6.36
Chromium oxide % - 0.02 0.02 0.02
Choline chloride % - 0.30 0.30 0.30
Total % - 100.00 100.00 100.00
Notes:
a
PF Pre-feeding, CL Cellulose, BD Beet pulp, RB Rice bran.
b
The values were based on as-fed basis and provided from Purina Mills, LLC (St. Louis, MO) except
where otherwise mentioned. All diets were formulated by the manufacturer to meet or exceed AAFCO (Association of American Feed Control Officials) requirements for
macro and micronutrients for dogs.
c
Thevalueswerecalculated,basedonthelatest(asofMarch2005) ingredient analysis information by Purina Mills,
LLC (St. Louis, MO) except where otherwise mentioned. Since nutrient composition of natural ingredients varies, analysis will differ accordingly.
d
PF diet; ingredients:
ground corn, ground brown rice, poultry by-product meal, poultry meal, corn glut en meal, dehulled soy bean meal, animal fat preserved with BHA (butylated
hydroxyanisole), poultry fat preserved with ethoxyquin, wheat middlings, poultry digest, calcium carbonate, dried whole eggs, dried beet pulp, brewers
dried yeast, soybean oil, dicalcium phosphate, salt, lecithin, pyridoxine hydrochloride, choline chloride, potassium chloride, menadione dimethylpyrimidinol
bisulfate, biotin, cholecalciferol, vitamin A aceta te, di-alpha tocopheryl acetate, inositol, DL-methionine, folic acid, calcium pantothenate, thiamin mononitrate,
ethoxyquin, nicotinic acid, riboflavin, cyanocobalamin, manganous oxide, ferrous sulfate, cobalt carbonate, coppe r sulfate, zinc oxide, sodium selenite.
e
Crude
fiber.
f
Total dietary fibers (TDF), dry-matter basis, analyzed by Dr. George C. Fahey Jr. in the Department of Animal Sciences, University of Illinois, Urbana,
IL 61801.
g
Amount of the ingre dients was decided by calculation based on the amount of TDF equal to the amount of TDF in the rice bran diet with 10 % full fat
rice bran.
h
Provided the following amounts of minerals and vitamins/kg diet: calcium 10 g, phosphorous 6.6 g, potassium 7 g, magnesium 0.5 g, sodium 4.6 g, chloride
6.7 g, fluoride 48 mg, iron 365 mg, manganese 55 mg, copper 12 mg, cobalt 0.4 mg, iodine 1.5 mg, chromium 2.3 mg, molybdenum 1.23 mg, selenium 0.46 mg, vitamin
A 10,900 IU, vitamin D-3 2,200 IU, vitamin E 44 IU, menadione 0.68 mg, thiamin hydrochloride 10.9 mg, riboflavin 4.9 mg, niacin 64 mg, pantothenic acid 20 mg, folic
acid 4.0 mg, pyridoxine 12.4 mg, biotin 0.2 mg, vitamin B-12 28 μg, choline chloride 2.1 g
Ko and Fascetti Journal of Animal Science and Technology (2016) 58:29 Page 3 of 10
CAAP. The PL samples remaining were stored at 20 °C
for determination of PL thiols. The frozen WB samples
were thawed and frozen three times to lyse the blood
cells, to release intracellular taurine, then diluted with
an equal volume of double deionized water (DDIW) and
deproteinized by the same method as described for PL.
Feces were stored at 20 °C. Each feces sample was
mixed with DDIW to obtain a slurry homogenate.
Approximately 100 g of the homogenate slurry of feces
was frozen at 20 °C for BA and protein assay.
Taurine concentrations of deproteinized PL, WB and
urine were measured using an amino acid analyzer
(Beckman 7300 Analyzer C7 Model, Beckman Instru-
ments, Fullerton, CA, USA). To normalize urinary tau-
rine concentration, urinary creatinine concentrations
were determined with a commercial kit (Cold Stable,
Pointe Scientific Inc., Canton, MI, USA). Deproteinized
PL CAAP was measured using an amino acid analyzer
(Biochrom 30, Biochrom Ltd., Cambridge, UK). In order
to quantify the concentrations of total cyst(e)ine (free
plus that bound to protein), cysteinyl-glycine and homo-
cysteine in PL and the concentrations of total glutathi-
one (GSH + GSSG) in WB, the combined and modified
HPLC method of Ubbink et al. [23] and Gilfix et al. [24]
was used. All of the volumes of reagents and samples
were scaled down to one-fourth to quantify thiol con-
centrations in PL and WB and, for WB total glutathione
concentrations. WB blood was diluted with an equal vol-
ume of DDIW before assay. Bile acid concentrations in
feces were measured using a commercial kit (Bile Acid
Kit No. 450-A, Trinity Biotech USA, Jamestown, NY,
USA) and BA in feces was extracted by the method of
Porter et al. [25] Apparent digestibility of dietary protein
was measured by calculation using dietary and fecal ni-
trogen concentrations. The concentrations of nitrogen,
protein and chromium in the diets and feces were analyzed
at Analytical Laboratory at the University of California
Davis.Totalnitrogenandtotalcrudeproteinwere
measured by a nitrogen gas analyzer (LECO FP-528,
LECO Corporation, St Joseph, MI, USA). Chromium
concentration was determined by Inductively Coupled
Plasma Atomic Emission Spectrometry (ICP-AES).
Statistical analysis
Significance of the data among three experimental
groups at each time point for all of the variables was an-
alyzed by mixed regression. Comparison of the variables
between two time points in a group was done by paired
t-test. All data were analyzed using SAS program [26].
All data in the report were expressed as mean ± SEM
unless otherwise mentioned. For all analyses, differences
were considered significant at P< 0.05. Probability values in
the range of 0.05P< 0.1 were considered as an indicator
of a noteworthy trend.
Results
During the experimental period, one dog in the BP
group ingested insufficient food to maintain BW and,
therefore, was removed from the experiment at week 10
(BCS was 3 out of 9; BW was 82 % of week 0 at week 3).
All of the data from the BP group were obtained from
the remaining five dogs after week 10. Except for that
dog, all of the dogs maintained BW and had normal
blood chemistries and completed blood cell counts at
the beginning of the experiment. However, at the end of
the experiment, the mean PL albumin concentrations
were 29 ± 2, 28 ± 1 and 29 ± 2 g/L for the CL, BP and RB
group, respectively, which are below of the lower end of
the reference range for PL albumin concentration of nor-
mal dogs (3044 g/L). The mean PL total protein concen-
trations, at the end of the experiment, were 66 ± 4, 62 ± 5
and 66 ± 3 g/L for the CL, BP and RB group, respectively.
These values are within the normal reference range for PL
total protein concentration of normal dogs (5476 g/L).
There were no significant differences among the groups in
PL albumin and total protein concentrations.
Mean food intakes (FI) of the dogs to maintain a BCS
of 5/9 were 515 ± 35, 543 ± 43, and 566 ± 70 g/day for
CL, BP and RB groups, respectively during the adapta-
tion period and were 426 ± 11, 443 ± 14, and 425 ± 10 g/day
for CL, BP and RB groups, respectively, during the experi-
mental period. No significant differences among the groups
were found throughout the study. Mean BW of the dogs at
the end of the study were 24.8 ± 0.4, 27.1 ± 1.4 and 28.1 ±
1.3 kg for CL, BP and RB groups, respectively. No statistical
differences in BW occurred among the groups during the
experiment except that the CL group had lower BW than
theRBgroupfromweek9toweek12(P< 0.05). The BCS
of all dogs were maintained between 4 and 6 throughout
the study.
Plasma taurine concentrations decreased to under
40 μmol/L for all the groups (Fig. 1a) during the experi-
mental period. The BP group decreased taurine concen-
trations lower than the other 2 groups from week 4 to
the end of the experiment (P< 0.01) and the CL group
maintained the highest mean PL taurine concentrations
from week 6, but was significantly higher than the other
two groups only at week 10 (P< 0.01). Whole blood tau-
rine concentrations showed a similar pattern as those of
PL taurine concentrations but the rates of decrease were
slower (Fig. 1b). From week 6, the WB taurine concen-
tration in BP group was lower than the other two groups
(P< 0.01) with no statistical differences between the CL
and RB groups. Urinary taurine excretions were markedly
decreased from week 0; 3981 ± 790, 8880 ± 4496 and
5858 ± 910 nmol/ml/mg creatinine to week 12; 85 ± 7,
101 ± 23 and 120 ± 19 nmol/ml/mg creatinine for CL,
BP and RB groups, respectively (ie, at week 12, only 2.1,
0.8 and 0.8 %, respectively of the week 0 values).
Ko and Fascetti Journal of Animal Science and Technology (2016) 58:29 Page 4 of 10
However no statistical differences were found among
the3groupsatanytimepoint.
Mean apparent protein digestibilities of the diets for
the dogs were 88.8 ± 0.6, 81.9 ± 0.6 and 88.1 ± 1.2 % for
CL, BP and RB groups, respectively. The BP group had
the lowest protein digestibility from week 2 to week 12
(P< 0.001) and the RB group had a protein digestibility
lower than the CL group but higher than the BP group
at week 2, 4 and 8 (P< 0.05).
The concentrations of thiols in PL or WB of the 3
groups are shown in Fig. 2. Plasma total cyst(e)ine con-
centrations (Fig. 2a) for RB group appeared to be main-
tained better than the other two groups which decreased
during the experimental period. At week 8, the PL total
cyst(e)ine concentration was significantly higher in the
RB group than the BP group; at week 10, higher in the
RB group than the BP and the CL group; and at week12,
higher in the RB than the CL group (P< 0.05). Total
glutathione (GSH + GSSG) in WB (Fig. 2b) did not show
any significant differences among the groups. However,
the mean concentrations of total glutathione in WB at
week 12 of the CL, BP and RB groups increased by 46,
65, and 49 % from those at week 2 (P< 0.01). Plasma
cysteinyl-glycine (Fig. 2c) and homocysteine (Fig. 2d)
had similar patterns. The concentrations decreased be-
tween week 2 and week 4 and remained low until the end
of the experiment. Only PL cysteinyl-glycine concentra-
tions at weeks 10 and 12 between BP and RB, developed
statistical differences (P< 0.05). The PL cysteinyl-glycine
concentrations at week 12 were approximately 45, 47, and
45 % of those at week 2 (P< 0.01) and in PL homocysteine
concentrations at week 12 were approximately 50, 37, and
Fig 1 Concentrations of plasma (PL) and whole blood (WB) taurine among groups during 12 weeks of the experiment. aand bshow taurine
concentrations in PL and WB of dogs, respectively, fed the purified diets containing different fiber sources. The values are expressed as mean± SEM.
The symbols represent the groups that have significant differences (P< 0.05 unless otherwise mentioned in the text) at the time point (*significance
between BP and RB, **significance between BP and CL, and ***significance between RB and CL). From week 10, n= 5 for the BP group due to omission
of one dog for excessive weight loss
Ko and Fascetti Journal of Animal Science and Technology (2016) 58:29 Page 5 of 10
45 % of those at week 2 (P< 0.01) for the CL, BP and RB
group, respectively.
Plasma free cysteine (not including that bound to plasma
proteins) and methionine concentrations were determined
with the PL CAAP. At week 2, PL free cysteine in the BP
group was significantly lower than the RB group (P< 0.05)
with a noteworthy trend lower than the CL group (p=
0.08, 34 ± 3, 26 ± 4 and 36 ± 3 μmol/LforCL,BPandRB
groups, respectively). However, at week 12, PL free cysteine
concentrations among the two groups did not show any
significant differences (23 ± 1, 25 ± 4 and 28 ± 5 μmol/L for
CL, BP and RB groups, respectively). Plasma methionine
concentrations did not show any significant differences
among groups or with time. The mean PL methionine con-
centrations for CL, BP and RB group at week 0 were 53 ±
4, 56 ± 6 and 64 ± 7 μmol/L, respectively and at week 12
were 60 ± 2, 56 ± 2 and 51 ± 6 μmol/L, respectively.
Bile acid excretions of the dogs for the study are shown
in Table 2. Throughout the study, the BP group had higher
BA excretion than those of CL and RB regardless of the
method of expression (P<0.01).
Discussion
Food intake of the dogs decreased when the diets were
changed from the PF diet to the experimental purified
diets. Average FI of the dogs for the last two weeks of
the adaptation period for the PF diet was 26 % higher
than that for the experimental period for the purified
diets. Decrease of FI after changing diets was mainly due
to the characteristic differences of the diets. Purified
diets have higher digestible energy as compared to the
diets consisting of natural food ingredients. In this study,
the energy (Table 1) of the PF diet (15.0 kJ/g diet) was
about 2025 % lower than those of the three purified
diets (19.2 kJ/g diet, 18.7 kJ/g diet and 17.5 kJ/g diet for
CL, BP and RB diet, respectively). However, the dogs
throughout the study maintained BCS levels between 4
and 6. Food intake and protein intake throughout the
study appeared to be adequate to maintain BW, even
though the protein content of the purified diets was lim-
ited to about 12 % of their diets. However, the decrease
in PL albumin below the normal reference range for all
of three groups indicates that either total protein or an
Fig 2 Various thiol concentrations in plasma (PL) and whole blood (WB) of the dogs fed the purified diets containing various fiber sources. aPL
total cysteine (free + bound); bWB total glutathione (GSH + GSSG); cPL cysteinyl-glycine; dPL homocysteine. The values are expressed as
mean ± SEM. The symbols represent the groups that have significant different (P< 0.05 unless otherwise mentioned in the text) at the time
point (*significance between BP and RB and ***significance between RB and CL). From week 10, n= 5 for the BP group due to omission of
one dog for excessive weight loss
Ko and Fascetti Journal of Animal Science and Technology (2016) 58:29 Page 6 of 10
essential amino acid may have been slightly limiting for
normal albumin homeostasis. Except for branched chain
amino acids, none of the concentrations of essential
amino acids in the PL during the experimental period
were lower than those at week 0 (data not shown) and
all were within the normal range for dogs [27]. The
branched chain amino acids for weeks 8 and 12 were
about 6469 % of the concentrations found at week 0
(forPFdiet)whichwereaboutatthefirstquartileofnor-
mal concentrations for dogs [27]. It would therefore appear
that cyst(e)ine (60 % of the first quartile of the normal
cyst(e)ine concentration) was the most limiting amino acid
for protein synthesis as well as for taurine synthesis.
Mean taurine concentrations (Fig. 1) of the dogs at
week 12 were 20.4 ± 3.9, 6.7 ± 0.5 and 13.1 ± 1.0 μmol/L
for PL and 143 ± 14, 79 ± 10 and 127 ± 14 μmol/L for
WB for the CL, BP and RB groups, respectively. Since
the lower limits for PL and WB taurine concentration
for preventing a risk for DCM in dogs are 40 μmol/L and
180 μmol/L, respectively [3], all of dogs that were partici-
pating in this study were taurine deficient by studys
end. There appears to be three reasons for the taurine
deficiency in this study.
The first is protein digestibility (sulfur amino acid
bioavailability). The BP group showed the lowest protein
digestibility throughout the study among the three experi-
mental groups and, therefore it would be predicted that
less sulfur amino acids were available for taurine synthesis.
The digestibility of protein in animals fed diets containing
BP has been reported by various researchers. Several have
reported no effect of BP on protein digestibility in horses
[28], cats [29], and even in dogs [30]. In contrast, reports
in pigs [31] and in chickens [32], indicate that protein
digestibility was decreased when fed BP. It is known
that taurine is a non-essential amino acid that is syn-
thesized in most mammals from cyst(e)ine [33]. Our re-
sults indicate that when protein, and thus sulfur amino
acids, are low yet sufficient for nitrogen balance and
glutathione homeostasis, taurine synthesis is inadequate
and that a decrease in protein digestibility may be a part
of this process. Therefore, the key to a diet providing ad-
equate taurine synthesis in dogs would be an adequate
quantity of bio-availablesulfur amino acids. That quan-
tity appears to be more than we had in the diets of the
present experiment.
The second possible reason is the effects of fibers that
would interfere with the entero-hepatic recycling of BA,
the recycling route for the major taurine metabolite to
maintain taurine status. Fibers have various physiological
effects on the metabolism of animals, including satiety,
slowing gastric emptying, thus delaying or interfering
with nutrient absorption that, in turn, results in im-
provement of glucose tolerance and lowering serum
cholesterol [34]. There are several hypotheses regarding
the cholesterol-lowering effect of fiber, which include
increasing BA excretion through feces. Since most dogs
diagnosed with DCM had been fed lamb and rice (includ-
ing RB) diets, we postulated that RB may contribute to the
low taurine status of these dogs [5]. In general, BAs are
synthesized in liver from cholesterol and conjugated with
glycine or taurine to make these strong detergents, glyco-
cholic acid or taurocholic acid. These detergents play an
important role in the small intestine to emulsify various
kinds of lipids to enhance their absorption by forming
water soluble micelles. After functioning, the bile salts are
recycled via passive diffusion in the small intestine and via
receptor-mediated transport in the lower ileum with ap-
proximately 99 % of recycling efficiency [33]. Dogs, like
cats, obligatorily conjugate BA with taurine, ie, the liver
enzyme responsible for conjugation, cholyl-CoA:N-acyl-
transferase, is specific for taurine in dogs [34]. An interfer-
ence with entero-hepatic recycling of bile salts would
result in the depletion of the taurine pool of dogs if a lim-
ited quantity of taurine or its precursors are available.
Therefore, fecal BA excretion was determined as an in-
dicator of the efficiency of entero-hepatic recycling of
bile salts of the dogs fed the various fibers. Fecal BA ex-
cretions, on a dry matter basis, gradually decreased in
all 3 groups (P< 0.01), apparently the result of switching
from commercial diet to the purified diets. However, the
Table 2 Bile acid excretion in dogs fed the purified diets containing various fiber sources
c
μmol/g feces (DM
e
-basis) μmol/5 day
Time CL
e
BP
e
RB
e
CL
e
BP
e
RB
e
Week 0 5.17 ± 0.64
a
7.03 ± 0.71
b
5.76 ± 0.38
ab
1123 ± 155 869 ± 120 1008 ± 67
Week 2 5.27 ± 0.62 6.56 ± 0.48 5.96 ± 0.21 944 ± 165 1145 ± 104 1047 ± 237
Week 4 4.53 ± 0.51
a
7.40 ± 0.27
b
5.17 ± 1.12
ab
597 ± 119
a
1053 ± 104
b
721 ± 97
a
Week 6 4.21 ± 0.63 4.18 ± 0.89 2.96 ± 0.39 684 ± 80 948 ± 241 514 ± 71
Week 8 2.69 ± 0.33
a
5.34 ± 0.65
b
4.93 ± 0.75
b
487 ± 95
a
868 ± 141
b
693 ± 71
ab
Week 10 3.32 ± 0.32
ab
4.63 ± 0.84
a
2.62 ± 0.34
b
562 ± 92
ab d
737 ± 146
a
401 ± 52
b
Week 12 3.43 ± 0.54
a
5.60 ± 0.14
b
3.42 ± 0.35
a
513 ± 111
ad
946 ± 177
b
555 ± 64
a
Notes:
ab
The letters superscripted represent significant differences between groups (P< 0.05).
c
The values are expressed as mean ± SEM, n= 6 for each group.
d
n= 5 due to omission of one dog for excessive weight loss.
e
DM Dry matter, CL Cellulose, BP Beet pulp, RB Rice bran
Ko and Fascetti Journal of Animal Science and Technology (2016) 58:29 Page 7 of 10
excretion of BA/5 days by week 12 for the BP group was
nearly twice that of the CL or RB group. Possible reason
for decrease of fecal BA excretion with time may be the
limited amount of protein in the diets. The synthesis and
secretion of BA are reported to be enhanced by the hor-
monal stimulation of cholecystokinin whose release is
evoked by fats and amino acids in the digestive tracks of
the animals [35]. That is, the lower consumption of pro-
tein by the dogs may have led to less release of cholecysto-
kinin and, in turn, less BA production and secretion.
However, it is clear that the BP group had the highest BA
excretion regardless of the method of expression. Even
though the initial fecal BA excretion of the BP group on a
dry matter basis was the highest, the BA excretions at
week 12 were 64, 80, and 59 % of the BA excretions at
week 0 for CL, BP and RB groups, respectively, showing
that the BP group had the lowest percentage decrease. By
analyses, the TDF of the CL, BP and RB diets (Table 1)
were 2.51, 1.98, and 2.68 %, respectively, demonstrating
that the BP fiber effect was not the result of more dietary
fiber. Moreover, all had about the same percentage of in-
soluble dietary fiber, 1.83, 1.98 and 1.81 % for CL, BP and
RB diets, respectively and all had about 1 % crude fiber.
Thus, it does not appear that it is the quantity of the vari-
ous fibers, but the nature of the fiber that is contributing
to the different response of the BP on BA excretion and
taurine depletion.
The third possible reason for the decrease in taurine
status in the present study is the interaction of fiber with
the small intestinal microbes. Thus, the difference be-
tween the overall effects of the three dietary treatments on
taurine status may reside in the difference in fermentabil-
ity of the fibers by the small intestinal microbes. If an in-
creased microbial fermentation occurs as the result of an
increased consumption of BP fiber as compared to the
fiber in CL or RB, then it would be expected that more
taurine would be destroyed, similar to the increase catab-
olism of taurine that occurs in cats that have more micro-
bial fermentation [1315, 36]. Sunvold et al. [37] have
reported that BP supports a greater rate of fermentation
than CL, and even if BP has no soluble fiber (ie, 100 % in-
soluble finer), it is still considerably more fermentable
than CL. Thus, although we could not rule out some
microbial fermentation by the CL or RB groups because
we had no control diet without fiber, the results still sup-
port the idea that BP, not RB, fiber may contribute to a
significant loss of endogenous taurine in dogs.
WiththepossibleexceptionoffreeandtotalPL
cyst(e)ine, there is no indication that there was an effect of
fiber on body thiol status (Fig. 2). Although total PL
cyst(e)ine (free + bound) was somewhat lower in the BP
group at 4 of the time points, it was never significantly
lower than the CL group, suggesting that it was not a de-
crease in PL cyst(e)ine alone that was the cause of the
lower PL taurine in the BP group, even though it is appar-
ent that there was not enough dietary sulfur amino acids
(more specifically, hepatic cysteine) for any group to
synthesize adequate taurine. Plasma free cysteine (cysteine
not bound to protein) concentrations in the current
experiment were already depleted in the BP group
(26 ± 4 μmol/L) at week 2 and were maintained until the
end of the study (25 ± 4 μmol/L), whereas the other 2
groups, although decreasing at week 2 (34 ± 3 μmol/L and
36 ± 3 μmol/L for CL and RB group, respectively),
were not as depleted as the BP group until week 12
(23 ± 1 μmol/L and 28 ± 5 μmol/L for CL and RB group,
respectively) supporting the idea that dietary BP decreases
the bioavailability of cysteine in the diet, thus contributing
to the depletion of taurine in dogs.
Whole blood was chosen for total glutathione assay
since red blood cells contain the higher concentration of
glutathione. Although glutathione is known as a reser-
voir for cysteine [38], it is interesting that in the present
experiment glutathione did not decrease after feeding
the low protein diets but actually increased about 20 % in
all groups. According to Stipanuk et al. [38] glutathione
concentration is regulated by the activity of glutamate-
cysteine ligase (known as γ-glutamyl-cysteine synthetase)
whose activity is regulated by the cellular concentration of
cysteine. When cellular cysteine is decreased, glutamate-
cysteine ligase is up-regulated to increase synthesis of
glutathione and when cellular cysteine is in excess,
cysteine dioxygenase is up-regulated to catabolize excess
cysteine to maintain a narrow range of tissue cysteine
concentrations. In this study, the concentrations of total
cysteine in PL at week 12 were approximately 75, 85 and
90 % of those of week 2 for CL, BP and RB group, respect-
ively. Free cysteine concentrations in PL at the end of the
study were 62, 49, and 46 % of those of week 0 for CL, BP
and RB group, respectively, perhaps indicating that free
cyst(e)ine is a better indicator of cysteine availability for
metabolic needs (including taurine synthesis) than total
cyst(e)ine (free plus that bound to protein via sulfhydryl
bonding).
It is interesting that metabolic regulation conserves
glutathione rather than taurine, perhaps simply because
the dietary excess of sulfur amino acids goes through the
liver first where the majority of the enzymes involved are
located and because of the Kms of the enzymes involved.
That is, the priority for the use of cysteine in dogs in our
experiment appears to be first for glutathione, second for
general protein synthesis and finally for taurine synthesis.
The apparent anomaly (ie, of glutathione being a reservoir
for cyst(e)ine) here is that there appeared to be insufficient
albumin synthesis or increased albumin breakdown under
the conditions of our experiment, even though the dogs
appeared to be in nitrogen balance (ie, maintaining BW)
and WB total glutathione actually increased.
Ko and Fascetti Journal of Animal Science and Technology (2016) 58:29 Page 8 of 10
Conclusion
In summary, rather than RB, dietary BP showed the
most significant effect in lowering PL and WB taurine
concentrations, in part, by decreasing the protein digest-
ibility (sulfur amino acid bioavailability), by enhancing fecal
excretion of BA and possibly, by enhancing degradation of
taurinebygutmicrofloraindogs.Theseeffectsmayresult
from the greater effect of BP fiber than RB or CL on intes-
tinal bacterial fermentation that cleaves taurocholic acid
and destroys the taurine released. In conclusion, since CL
was the control fiber, and RB caused similar responses as
CL, we conclude that RB is unlikely the cause of the
increased risk of taurine deficiency in dogs fed lamb
and rice diets.
Acknowledgement
The research was supported by, the Center for Companion Animal Health at
the School of Veterinary Medicine, University of California Davis; Margery
Reibold Sommer Memorial Endowment, Department of Molecular
Biosciences, University of California Davis and Purina TestDiet®/LabDiet®,
Richmond, IN.
The authors thank to Dr Quinton Roger who provided fundermental ideas
and guidance for the research, the staffs of Covance Research Product Inc.
(Kalamazoo, MI) for their technical work in collecting the samples and
Zengshou Yu at the Department of Molecular Biosciences at UC Davis
(Davis, CA) for taurine and amino acid analyses.
Funding
Not applicable.
Availability of data and materials
All data and materials to generate this manuscript are available with authors.
Authorscontributions
KS KO designed and performed the major part of experiments and wrote
the manuscript. AJF cooperated in analyes and writing the manuscript.
All authors read and approved the final manuscript.
Competing interests
The authors declare that they have no competing interest.
Consent for publication
All authors agree for this manuscript to be published.
Ethics approval and consent to participate
The husbandry and treatments of the animals for the study were approved
by the Animal Use and Care Administrative Advisory Committee at the
University of California, Davis and the dogs in this study were taken care of
in compliance with the National Research Council [18] guidance for
laboratory animals.
Received: 8 July 2016 Accepted: 22 July 2016
References
1. Hayes KC. Taurine nutrition. Nutr Res Rev. 1998;1:99113.
2. Torres CL. The effects of dietary ingredients, bacterial degradation in the
gut and amount of food consumed on taurine status of dogs of different
body sizes (dissertation). CA, USA: University of California Davis; 2003.
3. Backus RC, Cohen G, Pion PD, et al. Taurine deficiency in Newfoundlands
fed commercially available complete and balanced diets. J Am Vet Med
Assoc. 2003;223:11306.
4. Backus RC, Ko KS, Fascetti AJ, et al. Low plasma taurine concentrations in
Newfoundland dogs is associated with low plasma methionine and
cyst(e)ine concentrations and low taurine synthesis. J Nutr. 2006;136:252533.
5. Fascetti AJ, Reed JR, Rogers QR, et al. Taurine deficiency in dogs with
dilated cardiomyopathy: 12 cases (1997-2001). J Am Vet Med Assoc.
2003;223:113741.
6. Johnson ML, Parsons CM, Fahey GC, et al. Effects of species raw material
source, ash content, and processing temperature on amino acid digestibility
of animal by-product meals by cecectomized roosters and ileallycannulated
dogs. J Anim Sci. 1998;76:111222.
7. Stratton-Phelps M, Backus RC, Rogers QR, et al. Dietary rice bran decreases
plasma and whole-blood taurine in cats. J Nutr. 2002;132:1745s7s.
8. Topping DL, Illman RJ, Roach PD, et al. Modulation of the hypolipidemic
effect of fish oils by dietary fiber in rats: studies with rice and wheat bran.
J Nutr. 1990;120:32530.
9. Hundemer JK, Nabar SP, Shriver BJ, et al. Dietary fiber sources lower blood
cholesterol in C57BL/6 mice. J Nutr. 1991;121:13605.
10. Kahlon TS, Chow FI, Sayre RN, et al. Cholesterol-lowering in hamsters fed
rice bran at various levels, defatted rice bran and rice bran oil. J Nutr.
1992;122:5139.
11. Tomlin J, Read NW. Comparison of the effects on colonic function caused
by feeding rice bran and wheat bran. Eur J Clin Nutr. 1998;42:85761.
12. Gerhardt AL, Gallo NB. Full-fat rice bran and oat bran similarly reduce
hypercholesterolemia in humans. J Nutr. 1998;128:8659.
13. Gestel G, Besancon P, Rouanet JM. Comparative evaluation of the effects of
two different forms of dietary fibre (rice bran vs. wheat bran) on rat colonic
mucosa and faecalmicroflora. Ann Nutr Metab. 1994;38:24956.
14. Kim SW, Rogers QR, Morris JG. Dietary antibiotics decrease taurine loss in
cats fed a canned heat-processed diet. J Nutr. 1996;126:50915.
15. Kim SW, Rogers QR, Morris JG. Maillard reaction products in purified diets
induce taurine depletion in cats which is reversed by antibiotics. J Nutr.
1996;126:195201.
16. Torres CL, Backus RC, Fascetti AJ, et al. Taurine status in normal dogs fed a
commercial diet associated with taurine deficiency and dilated
cardiomyopathy. J Anim Physiol Anim Nutr. 2003;87:35972.
17. National Research Council. Nutrient requirements of dogs and cats, Rev.
Washington D.C: National Academy Press; 2006.
18. National Research Council. Guide for the care and use of laboratory animals.
Washington D.C: National Academy Press; 1996.
19. Mawby DI, Bartges JW, Laflamme DP, et al. Comparison of various methods
for estimating body fat in dogs. J Am Anim Hosp Assoc. 2004;40:10914.
20. Allison JB, Anderson JA, Seeley RD. Some effects of methionine on the
utilization of nitrogen in the adult dog. J Nutr. 1947;33:36170.
21. Kade CF, Phillips JH, Phillips WA. The determination of the minimum
nitrogen requirement of the adult dog for maintenance of nitrogen
balance. J Nutr. 1948;36:10921.
22. Arnold A, Schad JS. Nitrogen balance studies with dogs on casein or
methionine-supplemented casein. J Nutr. 1954;53:26573.
23. Ubbink JB, Hayward Vermaak WJ, Bissbort S. Rapid high-performance liquid
chromatographic assay for total homocysteine levels in human serum.
J Chromatogr. 1991;565:4416.
24. Gilfix BM, Blank DW, Rosenblatt DS. Novel reductant for determination of
total plasma homocysteine. Clin Chem. 1997;43:6878.
25. Porter JL, Fordtran JS, Santa Ana CA, et al. Accurate enzymatic
measurement of fecal bile acids in patients with malabsorption. J Lab Clin
Med. 2003;141:4118.
26. Institute SAS. SAS system for windows, release 8.2. Cary: SAS Institute; 2001.
27. Delaney SJ, Kass PH, Rogers QR, et al. Plasma and whole blood taurine in
normal dogs of varying size fed commercially prepared food. J Anim
Physiol Anim Nutr. 2003;87:23644.
28. Olsmanm AF, Huurdeman CM, Jansen WL, et al. Macronutrient digestibility,
nitrogen balance, plasma indicators of protein metabolism and mineral
absorption in horses fed a ration rich in sugar beet pulp. J Anim Physiol
Anim Nutr. 2004;88:32131.
29. Fekete SG, Hullar I, Andrasofszky E, et al. Effect of different fibre types on the
digestibility of nutrients in cats. J Anim Physiol Anim Nutr. 2004;88:13842.
30. Cole JT, Fahey Jr GC, Merchen NR, et al. Soybean hulls as a dietary fiber
source for dogs. J Anim Sci. 1999;77:91724.
31. Graham H, Hesselman K, Aman P. The influence of wheat bran and sugar-
beet pulp on the digestibility of dietary components in a cereal-based pig
diet. J Nutr. 1986;116:24251.
32. Pettersson D, Razdan A. Effects of increasing levels of sugar-beet pulp in
broiler chicken diets on nutrient digestion and serum lipids. Br J Nutr.
1993;70:12737.
Ko and Fascetti Journal of Animal Science and Technology (2016) 58:29 Page 9 of 10
33. Tso P, Crissinger K. Overview of digestion and absorption, in Biochemical
and physiological aspects of human nutritio. PA, USA: W. B. Saunders
Company; 2003.
34. Czuba B, Vessey DA. Identification of a unique mammalian species
of cholyl-CoA: amino acid N-acyltransferase. Biochim Biophys Acta.
1981;665:6124.
35. Jones PJH, Stanley K. Lipid, sterols, and their metabolites, in Modern
nutrition in health and disease. 9th ed. PA, USA: Lippincott Williams &
Wilkins; 1999.
36. Hickman MA, Rogers QR, Morris JG. Effect of processing on fate of dietary
[
14
C]taurine in cats. J Nutr. 1990;120:9951000.
37. Sunvold GD, Fahey Jr GC, Titgemeyer EC, et al. Dietary fiber for dogs: IV. In
vitro fermentation of selected fiber sources by dog fecal inoculum and in
vivo digestion and metabolism of fiber-supplemented diets. J Anim Sci.
1995;73:1099109.
38. Stipanuk MH, Dominy Jr JE, Lee JI, et al. Mammalian cysteine metabolism:
new insights into regulation of cysteine metabolism. J Nutr. 2006;136:1652S9S.
We accept pre-submission inquiries
Our selector tool helps you to find the most relevant journal
We provide round the clock customer support
Convenient online submission
Thorough peer review
Inclusion in PubMed and all major indexing services
Maximum visibility for your research
Submit your manuscript at
www.biomedcentral.com/submit
Submit your next manuscript to BioMed Central
and we will help you at every step:
Ko and Fascetti Journal of Animal Science and Technology (2016) 58:29 Page 10 of 10
... These nutrients are vital in cardiac muscle function. This was observed in medium and large breed dogs given beet pulp (Ko and Fascetti, 2016). The study hypothesized that diets, which were formulated to meet AAFCO requirements, may not actually be meeting the dogs' nutritional needs due to fiber's negative effect on nutrient absorption (Ko and Fascetti, 2016). ...
... This was observed in medium and large breed dogs given beet pulp (Ko and Fascetti, 2016). The study hypothesized that diets, which were formulated to meet AAFCO requirements, may not actually be meeting the dogs' nutritional needs due to fiber's negative effect on nutrient absorption (Ko and Fascetti, 2016). Fiber can also influence fermentation byproducts from microbes in the hindgut and hinder reabsorption of taurine, even if taurine is biosynthesized in sufficient amounts (Ko and Fascetti, 2016). ...
... The study hypothesized that diets, which were formulated to meet AAFCO requirements, may not actually be meeting the dogs' nutritional needs due to fiber's negative effect on nutrient absorption (Ko and Fascetti, 2016). Fiber can also influence fermentation byproducts from microbes in the hindgut and hinder reabsorption of taurine, even if taurine is biosynthesized in sufficient amounts (Ko and Fascetti, 2016). Furthermore, fiber can affect nutrient absorption in multiple ways. ...
Article
Full-text available
Dilated cardiomyopathy (DCM) has been in the literature and news because of the recent opinion-based journal articles and public releases by regulatory agencies. DCM is commonly associated with a genetic predisposition in certain dog breeds and can also occur secondary to other diseases and nutritional deficiencies. Recent communications in veterinary journals have discussed a potential relationship between grain-free and/or novel protein diets to DCM, citing a subjective increase in DCM in dog breeds that are not known to have a genetic predisposition for the disease. This literature review describes clinical presentations of DCM, common sequelae, treatment and preventative measures, histopathologic features, and a discussion of the varied etiological origins of the disease. In addition, current literature limitations are addressed, in order to ascertain multiple variables leading to the development of DCM. Future studies are needed to evaluate one variable at a time and to minimize confounding variables and speculation. Furthermore, to prevent sampling bias with the current FDA reports, the veterinary community should be asked to provide information for all cases of DCM in dogs. This should include cases during the same time period, regardless of the practitioner’s proposed etiology, due to no definitive association between diets with specific characteristics, such as, but not limited to, grain-free diets and those containing legumes, novel protein diets, and those produced by small manufacturers to DCM in dogs. In summary, in order to determine if certain ingredients, categories of diets, or manufacturing processes are related to an increased risk of DCM, further studies investigating these variables are necessary.
... One possible explanation is dietary fiber which was linked to decreased taurine levels in dogs (17,18). Fiber increases the excretion of fecal bile acids, and since taurocholate is the most common bile salt in dogs, this leads to increased fecal loss of taurine (19,20). In addition to taurine loss, high dietary fiber decreases protein digestibility, resulting in decreased cysteine and methionine (precursors of taurine) bioavailability. ...
... In addition to taurine loss, high dietary fiber decreases protein digestibility, resulting in decreased cysteine and methionine (precursors of taurine) bioavailability. Again, while the slow carbohydrate digestibility of pulses has some beneficial health effects such as low glycemic index, high dietary fiber of pulses may exacerbate the already low taurine, cysteine and methionine found in grain-free diets (20,21). What is unclear is what component of dietary fiber is responsible for the increased fecal bile salt loss, decreased protein digestibility and decreased sulfur amino acid bioavailability. ...
Article
Grain-based carbohydrate sources such as rice comprise 30–50% of commercial pet foods. Some pet foods however have removed the use of grains and have instead incorporated pulses, such as peas and lentils, resulting in grain-free diets. The hypothesis was dog diets with higher levels of dietary fiber will produce a low glycemic response due to decreased rates of digestion and lowered bioavailability of all macronutrients and increased fecal bile salt excretion. This in turn was hypothesized to produce lower plasma concentrations of cysteine, methionine and taurine after 7 days of feeding each test diet in dogs. Six diets were formulated at an inclusion level of 20% available carbohydrate, using white rice flour (grain) or whole pulse flours from smooth pea, fava bean, red lentil or 2 different wrinkled pea varieties (CDC 4,140–4 or Amigold) and fed to beagles in a randomized, cross-over, blinded design. After 7 days feeding each diet, fasting blood glucose was the lowest in the lentil (3.5 ± 0.1 mmol/L) and wrinkled pea (4,140–4; 3.6 ± 0.1 mmol/L) diet periods, while peak glucose levels was lowest after feeding the lentil diet (4.4 ± 0.1 mmol/L) compared to the rice diet. Total tract apparent digestibility of all macronutrients as well as taurine differed among diets yet plasma taurine was not outside normal range. Decreased macronutrient and amino acid digestibility was associated with increasing amylose and dietary fiber content but the specific causative agent could not be determined from this study. Surprisingly, digestibility decreases were not due to increased bile salt loss in the feces since increasing dietary fiber content led to decreased fecal bile salt levels. In conclusion, although pulse-based canine diets have beneficial low glycemic properties, after only 7 days, these pulse-based diets decrease macronutrient and amino acid digestibility. This is likely related at least in part to the lower animal protein content, but on a long-term basis could put domestic dogs at risk for low taurine and dilated cardiomyopathy.
... While there are no studies that report taurine or other AA concentrations in dogs fed a PBD to compare our results to, there are studies that have investigated the impact of certain plant ingredients on taurine and AA concentrations in dogs and cats. In a study of healthy dogs fed a purified low protein diet, beet pulp, a natural source of dietary fiber, was shown to decrease protein digestibility and increase bile acid excretion thereby reducing circulating taurine levels [31]. In a different study, dogs fed commercially prepared traditional diets containing whole grain brown rice as the first plant ingredient had significantly lower whole blood taurine concentrations than dogs fed a diet with multiple plant protein sources [30]. ...
Article
Full-text available
Consumer demand for commercially prepared plant-based (PB) dog food is increasing, but studies evaluating the short- or long-term effects of PB diets on canine health are lacking. The objective of this study was to assess the short-term amino acid (AA), clinicopathologic, and echocardiographic findings in 34 client-owned dogs fed a commercial extruded plant-based diet (PBD) in which pea protein was the primary protein source and 4 control dogs fed a commercial extruded traditional diet (TD). Plasma AA and whole blood taurine concentrations were measured in dogs at baseline and after 4 weeks on the PBD or the TD. Hematologic, serum biochemical, and echocardiographic testing were performed at baseline and after 12 weeks on the PBD or the TD. Four dogs in the PBD group did not complete the study. All essential AAs, except methionine, were higher in dogs after 4 weeks on the PBD compared to baseline. Taurine (plasma and whole blood) was also higher after 4 weeks on the PBD compared to baseline. A meaningful difference was detected in whole blood taurine between the PBD group and the control group at 4 weeks (P = .026) with the PBD group being higher. Median hematologic and biochemical results for the PBD group were within normal limits at baseline and at 12 weeks. In the PBD group, left ventricular internal diastolic dimension (LVIDd, P = < .001) and normalized LVIDd (P = .031) were higher 12 weeks post-PBD compared to baseline. There were no meaningful differences in left ventricular internal systolic dimension (LVIDs), normalized LVIDs, or fractional shortening 12 weeks post-PBD. There was no statistical evidence of difference between the 2 groups of dogs for any of the echocardiographic parameters at baseline or at 12 weeks. Essential AA or taurine deficiency was not observed in this cohort of dogs fed a commercial extruded PBD. Additionally, clinically relevant hematologic, serum biochemical and echocardiographic alterations were not detected. Further research is required to determine if long-term static feeding of PB diets can meet and maintain AA and other nutrient targets in dogs.
... Although taurine deficiency may occur as a consequence of dietary deficiency of methionine or cysteine, there are other nutritional factors that may be involved, such as decreased bioavailability of these sulfur amino acids, abnormal enterohepatic bile acid recycling, altered taurine intestinal metabolism and urinary loss of taurine [27,34]. In the present study, the vegan food with low methionine concentration may represent a risk factor for the development of DCM. ...
Article
Full-text available
The objective of this study was to evaluate the macronutrients composition, fatty acid and amino acid profiles, and essential minerals content of all vegan foods for dogs and cats available in the Brazilian market, and to compare results with FEDIAF (2019) and AAFCO (2019) recommendations. Four vegan pet foods were assessed (three for dogs and one for cats). The comparisons were made in a descriptive manner. All foods met the minimum recommendations for macronutrients. Arachidonic acid was not reported in any food label. Regarding the FEDIAF recommendations, one food for dogs had low calcium, another had low potassium and a third had low sodium. The cat food presented potassium content lower than recommended. The Ca:P ratio did not meet the minimum recommendation of FEDIAF (2019) and AAFCO (2019) in any of the dog’s foods analyzed, and the cat food also did not present the minimum recommendation based on FEDIAF (2019). Copper concentrations exceeded the legal limit in all foods. Zinc concentrations exceeded this limit in two foods (one for dogs and one for cats) and iron levels exceeded the legal limit in one dog food. One of the dog foods did not meet the minimum recommendation for methionine and the cat food did not meet the minimum recommendation for arginine. In addition, when the amount of nutrients consumed by animals with low energy requirements was simulated, in addition to the same non-conformities described above, it was observed that the cat food does not meet the minimum recommended of protein and taurine in unit/Kg0.67. It was concluded that all foods analyzed had one or more nutrients below the recommended levels and some presented zinc and copper excess, therefore, these foods should not be recommended for dogs and cats, because dietary deficiencies found may lead to health risks for dogs and cats. Furthermore, manufacturers should review their formulations to ensure the nutritional adequacy of these foods.
... It has been hypothesized that diets containing high levels of fermentable fiber could lead to gastrointestinal losses of taurine through the BA cycle (Mansilla et al., 2019). Ko and Fascetti (2016) reported that beet pulp, a moderately fermentable fiber can affect taurine status in dogs by decreasing protein digestibility and increasing excretion of BA. However, these previous results were observed in dogs fed purified diets, which are not representative of commercial diets available in the market. ...
Article
Full-text available
This study evaluated the effects of a grain-based (GB) and grain-free (GF) diet on protein utilization and taurine status in healthy Beagle dogs. Two practical dog diets sufficient in crude protein, sulfur amino acids, and taurine content were formulated with the same ingredients with exception of the carbohydrate sources. The GB contained sorghum, millet, and spelt while potatoes, peas, and tapioca starch were used in the GF. A total of 12 Beagle dogs were used in a completely randomized design with six replicates per treatment. The study consisted of an adaptation period of two weeks followed by an experimental period of 28 d in which GB and GF were fed to the dogs. At the end of the adaptation period and every two weeks after it (d 0, d 14, d 28), markers of taurine metabolism were analyzed in whole blood (taurine), plasma (taurine, methionine, and cystine), urine (taurine:creatinine), and fresh fecal samples (primary and secondary bile acids). Fecal samples were collected during the last 6 days of experimental period for digestibly assessment using titanium dioxide as an external marker. Taurine markers and digestibility data were analyzed in a repeated measures model and one-way ANOVA, respectively, using PROC GLIMMIX in SAS (version 9.4). Apparent crude protein digestibility was not affected by treatment, but dogs fed GF diet had lower apparent organic matter digestibility compared to those fed GB (P < 0.05). Greater plasma taurine concentrations were observed at d 14 and d 28 compared to d 0; wherein dogs fed GF exhibited greater increase compared to those fed GB (P < 0.05). Whole blood taurine concentrations, plasma methionine concentrations, and urinary taurine:creatinine were also greater at d14 and d 28 compared to d 0 (P < 0.05), but no effect of diet was observed. Total bile acid excretion was similar between GF and GB groups, but dogs fed GF excreted a higher proportion of primary bile acids compared to those fed GB (25.49 vs 12.09% at d 28, respectively). In summary, overall taurine status was not affected by dietary treatments, however, our results suggest that the higher content of oligosaccharides and soluble fibers in the GF diet may alter the composition of the fecal bile acid pool.
... It has been hypothesized that diets containing high levels of fermentable fiber could lead to gastrointestinal losses of taurine through the BA cycle (Mansilla et al., 2019). Ko and Fascetti (2016) reported that beet pulp, a moderately fermentable fiber can affect taurine status in dogs by decreasing protein digestibility and increasing excretion of BA. However, these previous results were observed in dogs fed purified diets, which are not representative of commercial diets available in the market. ...
Article
Consumption of grain-free (GF) diets has recently been linked to canine dilated cardiomyopathy in selected dog breeds. Soluble fiber present in GF carbohydrate sources may be contributing to taurine depletion, thus affecting heart health. The objective of this study was to evaluate the effects of different carbohydrate sources on taurine status in healthy Beagle dogs. Two practical diets sufficient in sulfur-amino acids and taurine were formulated with the same proportion of carbohydrate sources: a grain-based (GB) containing sorghum, millet, and spelt, and a GF containing peas, potatoes and tapioca starch. Twelve Beagle dogs were fed experimental diets for 4-wk in a randomized complete block design. The morning prior to feeding experimental diets (baseline) and two and four weeks after, markers of taurine metabolism were analyzed in blood, urine, and fresh fecal samples. Data were analyzed as a change from baseline in a repeated measures model by GLIMMIX (SAS, version 9.4) in which the main effects of time, diet, and their interaction were evaluated. Greater concentrations of taurine in plasma (158 vs. 117 nmol/mL) and whole blood (254 vs. 234 nmol/mL) were observed during experimental period compared to baseline. An increase in plasma methionine was also observed during experimental period compared to baseline (64 vs. 57nmol/mL). Dogs fed GF exhibited higher plasma taurine concentration compared to those fed GB (181 vs. 138 nmol/mL). There were no significant effects of diet, time, or their interaction on plasma cystine concentration, urinary taurine:creatinine ratio, or total fecal bile acid (BA) excretion (P > 0.05). However, dogs fed GF had greater fecal primary BA (26 vs 14%) as a proportion of total BA compared to those fed GB. This study suggests that GF diets do not impair taurine blood concentration, but the increased proportion of fecal primary BA may decrease recycling of taurine through enterohepatic circulation.
Article
A recent association between the inclusion of pulses in canine diets and taurine deficiency has become a prevalent issue in the pet food industry. Although there is not a nutritional requirement for taurine by dogs, the appearance of taurine deficiencies has been related with more serious health issues, such as dilated cardiomyopathy. The objective of this study was to determine the circulating concentrations of plasma and whole blood taurine, indispensable and dispensable amino acid concentrations in the plasma, and taurine and creatinine concentrations in the urine of adult dogs fed a green lentil diet. Twelve, adult, female beagles were randomly assigned to a diet containing 45% green lentils (GLD) or a poultry byproduct meal diet (CON) for 90 days. Fresh urine samples were collected every 30 d and analyzed for taurine and creatinine concentrations. A blood sample also was collected every 30 d and analyzed for amino acids including taurine. Animal procedures were approved by the University of Illinois Institutional Animal Care and Use Committee. All diets were formulated to meet or exceed the nutrient requirements outlined by AAFCO (2018) and all dogs remained healthy throughout the study. The concentrations of taurine in the plasma and whole blood showed no differences (P > 0.05) between dietary treatments or across time points. Similarly, no differences (P > 0.05) in plasma methionine concentrations were observed between treatments or across time points. A treatment effect (P < 0.05) showed dogs fed GLD had higher total primary fecal bile acid (BA) excretion compared with dogs fed CON. The differential abundance of fecal microbial communities showed Firmicutes as the predominant phyla in dogs fed both GLD and CON, with Bacteroidaceae, Erysipelotrichaceae, and Lactobacillaecae as predominant families in dogs fed GLD. The α-diversity of dogs fed GLD ( P < 0.05) was lower than in dogs fed CON. These data suggest that the inclusion of 45% green lentil in extruded diets does not lower whole blood and plasma taurine concentrations during a 90 d period and is appropriate for use in a complete and balanced formulation for dogs.
Article
Full-text available
Bile acids (BA) are produced in the liver and conjugated with glycine or taurine before being released into the small intestine to aid with lipid digestion. However, excessive BA losses through feces can occur due to several dietary factors that in turn require greater production of BA by the liver due to a reduction in BA recycling. Consequently, net utilization of taurine and/or glycine is increased. To quantify this impact, we conducted a meta-analysis to investigate the effect of soluble fiber, diet composition, and species on fecal excretion of BA. After a systematic review of the literature, twelve studies met all inclusion criteria. Dietary carbohydrate, protein, fat, cellulose, cholesterol, soluble fiber and animal species were tested as independent variables. Mixed models were developed treating study as a random effect, and fixed effect variables were retained at P < 0.05 significance and where collinearity was absent between multiple X variables. A total of ten studies comprised of four species [(rat = 5), hamster (n = 1), guinea pig (n = 3) and dog (n = 1)], and 30 observations were evaluated in the final models after outlier removal. Model evaluation was based on the corrected Akaike Information Criteria, the concordance correlation coefficient and the root mean square prediction error. Three base models were developed, examining carbohydrate, protein and fat impacts separately. The best fitting models included the fixed effect of species and the interaction between soluble fiber (yes/no) and dietary carbohydrate, protein or fat (%, as-fed). Increased concentrations of dietary protein and fat resulted in greater fecal excretion of BA (P < 0.05). Conversely, increasing levels of dietary carbohydrate led to lower excretions of BA (P < 0.05). Increased dietary soluble fiber containing ingredients resulted in greater excretion of BA in all models (P < 0.05). Rats had greater excretion of BA compared to hamsters and guinea pigs (P < 0.05) in all models, and also compared to dogs (P < 0.05) in the carbohydrate model. The findings from this meta-analysis indicate that not only soluble fiber, but also increasing levels of dietary fat and protein may result in greater fecal excretion of BA, potentially altering taurine and/or glycine metabolism and affecting the need for diet delivery of these AA.
Article
Full-text available
Grain-free diets tend to have greater inclusions of pulses in contrast to grain-based diets. In 2018 the Food and Drug Administration (FDA) released a statement that grain-free diets may be related to the development of canine dilated cardiomyopathy (DCM). However, all dog foods met regulatory minimums for nutrient inclusion recommended by the Association of American Feed Controls Official (AAFCO). In some FDA case reports, but not all, dogs diagnosed with DCM also had low concentrations of plasma or whole blood taurine, as such we hypothesized that feeding these diets will result in reduced taurine status from baseline measures. The objective of this study was to determine the effects of feeding a grain-free diet to large breed dogs on taurine status and overall health. Eight Labrador Retrievers (4 males, 4 females; Four Rivers Kennel, MO) were individually housed and fed a commercial complete and balanced grain-free diet (Acana Pork and Squash formula; APS) for 26 wk. Fasted blood samples were collected prior to the start of the trial (baseline; wk 0), at wk 13 and wk 26 for analyses of blood chemistry, hematology, plasma amino acids (AA), and whole blood taurine. Urine was collected by free catch at wk 0 and 26 for taurine and creatinine analyses. Fresh fecal samples were collected at wk 0 and 26 for bile acid analyses. Data were analyzed using the GLIMMIX procedure with repeated measures in SAS (v. 9.4). Plasma His, Met, Trp, and taurine and whole blood taurine concentrations increased over the course of the study (P < 0.05). Urinary taurine to creatinine ratio was not affected by diet (P>0.05). Fecal bile acid excretion increased after 26 wk of feeding APS to dogs. Despite the higher fecal excretion of bile acids, plasma and whole blood taurine increased over the 26-wk feeding study. These data suggest the feeding APS, a grain-free diet, over a 26-wk period improved taurine status in Labrador Retrievers and is not the basis for incidence of DCM for dogs fed APS. Other factors that may contribute to the etiology of DCM should be explored.
Article
Methionine, an essential sulphur-containing amino acid (SAA), plays an integral role in many metabolic processes. Evidence for the methionine requirements of adult dogs is limited and we employed the Indicator Amino Acid Oxidation (IAAO) method to estimate dietary methionine requirements in Labrador retrievers (n=21). Using semi-purified diets, the mean requirement was 0.55g/1000kcal, with 95% confidence interval (CI) (0.41, 0.71). In a subsequent parallel design study, 3 groups of adult Labrador retrievers (n=52) were fed semi-purified diets with 0.55g/1000kcal (Test Diet 1), 0.71g/1000kcal (Test Diet 2) or 1.37g/1000kcal (Control Diet) of methionine for 32 weeks to assess the long term consequences of feeding. The total SAA content (2.68g/1000kcal) was maintained through dietary supplementation of cystine. Plasma methionine did not decrease in either test group and increased significantly on Test Diet 1 in weeks 8 and 16 compared to control. Reducing dietary methionine did not have a significant effect on whole blood, plasma or urinary taurine or plasma NT proBNP. Significant effects in both test diets were observed for cholesterol, betaine and dimethylglycine. In conclusion, feeding methionine at the IAAO-estimated mean was sufficient to maintain plasma methionine over 32 weeks when total SAA was maintained. However, choline oxidation may have increased to support plasma methionine and have additional consequences for lipid metabolism. While the IAAO can be employed to assess essential amino acid requirements, such as methionine in the dog using semi-purified diets, further work is required to establish safe levels for commercial diet formats.
Article
Full-text available
Article
Obesity is considered one of the most common forms of malnutrition occurring in dogs. Laboratory methods of evaluation of body composition in live dogs have included dual-energy X-ray absorptiometry (DEXA) and deuterium oxide (D(2)O) dilution. Clinical methods of evaluation include assigning a body condition score (BCS) based on visual observation, palpation, and morphometric measurements. This study used these four methods to evaluate 23 healthy, adult, client-owned dogs. Good correlation (coefficient of determination [r(2)]=0.78) was found between measurements of percent body fat (%BF) determined by the D(2)O dilution method and the DEXA scan. Percent body fat can also be estimated using BCS (r(2)=0.92 comparison with DEXA) or by using morphometric measurements with simple calculations (r(2)=0.92 comparison with DEXA).
Article
This study was conducted to determine the relative cholesterol-lowering effects of several levels of full-fat rice bran in hamsters. In addition, the separate effects of defatted rice bran and/or crude rice bran oil were investigated at levels equivalent to those present in 43.7% full-fat rice bran. Diets containing 10.9, 21.8, 32.8 or 43.7% full-fat rice bran, 35% defatted rice bran and/or 9% rice bran oil were fed to 4-wk-old male hamsters. All diets contained 10% total dietary fiber, 9% fat and 3.2% nitrogen; hypercholesterolemic diets contained 0.3% cholesterol; two diets were cholesterol-free, i.e., 10% cellulose and 43.7% full-fat rice bran. After 21 d, plasma and liver cholesterol, plasma triglycerides and liver weights were significantly greater in hamsters fed the 10% cellulose diet with 0.3% cholesterol compared with those fed the cholesterol-free cellulose diet. In animals fed cholesterol-free diets, plasma cholesterol values were significantly lower in those fed the 43.7% full-fat rice bran diet than in those fed the cellulose diet. In animals fed cholesterol-containing diets, plasma and liver cholesterol were significantly lower in animals fed the 43.7% full-fat rice bran diet than in those fed the cellulose diet. Plasma cholesterol reductions were significantly correlated to the level of rice bran in the diet. In cholesterol-fed hamsters, total liver cholesterol content was significantly lower in those fed the defatted rice bran diet with rice bran oil compared with those fed the cellulose diet. Full-fat rice bran was the only treatment that significantly lowered both plasma and liver cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
Five sources of dietary fiber were compared for their effect on blood and liver cholesterol. The effects of soybean fiber, rice bran (full fat), oat bran, barley bran and mixed bran on total blood cholesterol concentrations and liver cholesterol concentrations were measured in beef-fed C57BL/6 male mice. Each diet contained cooked beef, beef tallow, corn starch and 7% dietary fiber from one of the five fiber sources. A control group consumed a fiber-free diet. Dietary cholesterol was provided by the beef and beef tallow only. The experimental diets were fed for 3 wk; blood and liver were collected when the mice were 18 wk old. The liver cholesterol concentration in the rice bran-fed group was the lowest of the six diet groups and was significantly different than concentrations in the oat bran-fed group and the barley bran-fed group (P less than 0.05). The oat bran, mixed bran, and barley bran did not significantly lower blood cholesterol in the mice. Both the soybean fiber and rice bran diet groups had significantly lower total blood cholesterol than did the fiber-free controls (P less than 0.05). The soybean fiber group also had significantly lower blood cholesterol than the mixed-bran group.