TYPE Original Research
PUBLISHED 09 March 2023
DOI 10.3389/fvets.2023.1085890
OPEN ACCESS
EDITED BY
Bangyuan Wu,
China West Normal University, China
REVIEWED BY
Christopher Thomas,
Cardi University, United Kingdom
Marie Christine Cadiergues,
Ecole Nationale Vétérinaire de Toulouse
(ENVT), France
Jirayu Tanprasertsuk,
NomNomNow Inc., United States
*CORRESPONDENCE
Anna K. Shoveller
SPECIALTY SECTION
This article was submitted to
Animal Nutrition and Metabolism,
a section of the journal
Frontiers in Veterinary Science
RECEIVED 31 October 2022
ACCEPTED 10 February 2023
PUBLISHED 09 March 2023
CITATION
Richards TL, Burron S, Ma DWL, Pearson W,
Trevizan L, Minikhiem D, Grant C, Patterson K
and Shoveller AK (2023) Eects of dietary
camelina, flaxseed, and canola oil
supplementation on inflammatory and
oxidative markers, transepidermal water loss,
and coat quality in healthy adult dogs.
Front. Vet. Sci. 10:1085890.
doi: 10.3389/fvets.2023.1085890
COPYRIGHT
© 2023 Richards, Burron, Ma, Pearson,
Trevizan, Minikhiem, Grant, Patterson and
Shoveller. This is an open-access article
distributed under the terms of the
Creative
Commons Attribution License (CC BY)
. The use,
distribution or reproduction in other forums is
permitted, provided the original author(s) and
the copyright owner(s) are credited and that
the original publication in this journal is cited, in
accordance with accepted academic practice.
No use, distribution or reproduction is
permitted which does not comply with these
terms.
Eects of dietary camelina,
flaxseed, and canola oil
supplementation on inflammatory
and oxidative markers,
transepidermal water loss, and
coat quality in healthy adult dogs
Taylor L. Richards
1
, Scarlett Burron
1
, David W. L. Ma
2
,
Wendy Pearson
1
, Luciano Trevizan
3
, Debbie Minikhiem
4
,
Caitlin Grant
5
, Keely Patterson
1
and Anna K. Shoveller
1
*
1
Department of Animal Biosciences, University of Guelph, Guelph, ON, Canada,
2
Department of Human
Health and Nutritional Sciences, University of Guelph, Guelph, ON, Canada,
3
Department of Animal
Science, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil,
4
Consultant, Spring Hill, TN, United States,
5
Department of Clinical Studies, Ontario Veterinary College,
University of Guelph, Guelph, ON, Canada
Introduction: Camelina oil contains a greater concentration of omega-3 (n-3) a-
linolenic acid (C18:3n-3; ALA) than omega-6 (n-6) linoleic acid (C18:2n-6; LA),
in comparison to alternative fat sources commonly used to formulate canine
diets. Omega-3 FAs are frequently used to support canine skin and coat health
claims and reduce inflammation and oxidative stress; however, there is a lack
of research investigating camelina oil supplementation and its eects on these
applications in dogs. The objective of this study was to evaluate the eects of
camelina oil supplementation on coat quality, skin barrier function, and circulating
inflammatory and oxidative marker concentrations.
Methods: Thirty h ealthy [17 females; 13 males; 7.2 ± 3.1 years old; 27.4 ±
14.0 kg body weight (BW)] privately-owned dogs of various breeds were used.
After a 4-week wash-in period consuming sunflower oil (n6:n3 = 1:0) and a
commercial kibble, dogs were blocked by age, breed, and size, and randomly
assigned to one of three treatment oils: camelina (n6:n3 = 1:1.18), canola (n6:n3
= 1:0.59), flaxseed (n6:n3 = 1:4.19) (inclusion level: 8.2 g oil/100 g of total food
intake) in a randomized complete block design. Transepidermal water loss (TEWL)
was measured using a VapoMeter on the pinna, paw pad, and inner leg. Fasted
blood samples were collected to measure serum inflammatory and oxidative
marker concentrations using enzyme-linked immunosorbent assay (ELISA) kits
and spectrophotometric assays. A 5-point-Likert scale was used to assess coat
characteristics. All data were collected on weeks 0, 2, 4, 10, and 16 and analyzed
using PROC GLIMMIX in SAS.
Results: No significant changes occurred in TEWL, or inflammatory and oxidative
marker concentrations among treatments, across weeks, or for treatment by
week interactions. Softness, shine, softness uniformity, color intensity, and follicle
density of the coat increased from baseline in all treatment groups (P < 0.05).
Discussion: Outcomes did not dier (P > 0.05) among treatment groups
over 16-weeks, indicating that camelina oil is comparable to existing plant-
based canine oil supplements, flaxseed, and canola, at supporting skin
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Richards et al. 10.3389/fvets.2023.1085890
and coat health and inflammation in dogs. Future research employing an immune
or exercise challenge is warranted , as the dogs in this study were not subjected
to either.
KEYWORDS
omega-3, omega- 6, canine nutrition, skin and coat health, flaxseed oil, canola oil,
camelina oil
Introduction
Dogs are unable to produce the omega-6 (n-6) linoleic acid
(C18:2n-6; LA) and t he omega-3 (n-3) α-linolenic acid (C18:3n-3;
ALA), endogenously, and as such, these must be obtained in the
diet (
1). Omega-3 fatty acids (FAs) in particular have been linked to
numerous health benefits, including a reduction in inflammation
and oxidative stress, and improved skin and coat health properties,
which are directly associated (
2–7).
There is a competitive relationship between the n-6 and n-
3 FA pathways for the use of the 15- and 16-desaturase and
elongase enzymes needed to convert LA and ALA into longer chain
FAs. Consequently, a balanced dietary n-6:n-3 ratio is needed to
ensure sufficient conversion to longer chain FAs in both pathways.
Specifically, and most notably, L A is converted into arachidonic
acid (AA), and ALA is converted into eicosapentaenoic acid (EPA)
and docosahexaenoic acid (DHA) (
8). Both AA and EPA and
DHA are parent compounds for the production of pro- and anti-
inflammatory eicosanoids, respectively. An increase in endogenous
n-6 AA results in a prothrombotic, pro-constructive, and pro-
inflammatory state, whereas increased EPA and DHA give rise to
resolvins, which are anti-inflammatory and pro-resolving. Greater
concentrations of n-6 FAs and a higher n-6:n-3 ratio allow for
greater conversion of n-6 FAs to AA and more pro-inflammatory
effects. In contrast, greater concentrations of n-3 FAs and a lower
n-6:n-3 ratio allow for increased production of EPA and more
anti-inflammatory effects (
9). As a result, excessive amounts of n-
6 FAs and a high n-6:n-3 ratio promote the pathogenesis of many
inflammatory, autoimmune, and dermatological disorders, whereas
greater concentrations of n-3 FAs and a low n-6:n-3 ratio exert
suppressive effects (10).
In order to formulate canine diets to meet the ideal n-6:n-3
ratio of between 5:1 and 10:1, n-3 rich ingredients are typically
required (
11). Two oils commonly used to increase n-3 inclusion
in canine diets are fish oil, as a result of its high levels of EPA
and DHA (180 mg EPA, 120 mg DHA/1,000 mg of oil provided
in the most common fish oil capsules in the United States today,
however, doses vary widely between supplements), and flaxseed
oil, due to its favorable n-6:n-3 ratio of 1:4.19 (
12–15). However,
large-scale fish oil production required to meet the demands of
the growing pet food industry is not environmentally sustainable
long-term, and the high abundance of ALA in flaxseed oil makes it
susceptible to oxidation, making its use in commercial diets difficult
(
12, 15). Additionally, flaxseed crops are sensitive to various
climates, diseases, and pests, making both of these options less than
desirable (
12, 14, 15). Alternative animal-based (beef, 1:0.05; milk,
1:0.07; eggs, 1:0.05) and plant-based (canola, 1:0.59; corn, 1:0.01;
soybean, 1:0.12; and sunflower oil, 1:0.00) lipid sources commonly
used in canine diet formulations all have higher concentrations
of n-6 FAs rather than n-3 FAs (
15–17). This leaves room in the
market for an alternative plant-based oil source that is economically
and environmentally sustainable, with good shelf-stability and
a favorable concentration of n-3 FAs that could contribute to
achieving the ideal n-6:n-3 ratio in canine diets.
The oil seed camelina (C amelina sativa) is considered a
low-input, high-yield crop due to its short growing season and
resistance to various seasons, climates, and soil types (
18–21).
The product of this robust crop, camelina oil, provides a rich
source of n-3 FAs as a result of its desirable n-6:n-3 ratio of 1:1.8
(
22). Additionally, camelina oil contains high concentrations of
tocopherols and polyphenols, which have been associated with
improved skin and coat health due to their antioxidant properties
(
22). Due to camelina oil being naturally high antioxidants as well
as having a slightly lower concentrations of n-3 FAs in contrast to
flaxseed oil, it’s shelf-stability is better by comparison (
23).
Additional data from this study suggests camelina oil to be
safe for canine consumption (
24). The inclusion of oil supplements
in canine diets is often associated with claims of maintenance or
support of skin and coat health, but currently there is no data
directly comparing the effects of camelina oil supplementation to
the effects of other oils approved for use in pet foods on markers of
skin and coat health and inflammation. The objective of this study
was to compare the effects of dietary camelina oil supplementation
to those of flaxseed oil and c anola oil supplementation on
skin and coat health and inflammatory and oxidative markers
in healthy, adult dogs. Outcomes include changes in oxidative
and inflammatory biomarkers and coat quality. Additionally,
skin barrier function and integrity was assessed by measuring
transepidermal water loss (TEWL). Aut hors hypothesize that
camelina oil (n-3:n-6 = 1:1.8) is comparable, flaxseed (n-3:n-6 =
1:4.19) and canola oil (n-3:n-6 = 1:0.59) in terms of its effects on
oxidative and inflammatory markers, coat quality, and TEWL.
Materials and methods
Animals and housing
This experiment was approved by the University of Guelph’s
Animal Care Committee (AUP #4365) and was carried out in
accordance with national and institutional guidelines for the
care and use of animals. Thirty client-owned, adult (7.2 ± 3.1
years) dogs of mixed sex (17 females: 16 spayed, one intact; 13
males: 10 neutered, three int act), weight (27.4 ± 14.0 kg) and
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TABLE 1 Mean age, mean body weight, breeds, and male:female and neutered:spayed:intact ratios of 30 client-owned dogs enrolled in a research trial
investigating the eects of three oil supplements (camelina, canola, flaxseed) on transepidermal water loss, inflammatory and oxidative markers, and
coat quality over a 16-week period.
Treatment Mean age (years)
a
Mean BW (kg)
b
Breeds Male:female Neutered:spayed:intact
Miniature dachshund
Havanese
Mix, unknown
CAM 7.8 25
Mix, Australian shepherd/collie
2:8 2:7:1
Mix, boxer whippet
Standard poodle
Norwegian elkhound
Labrador retriever (3)
Miniature dachshund
Pekingese
Mix, sled dog/unknown
Mix, border collie/sheltie
FLX 7.7 27 Mix, husky/pointer 6:4 5:4:1
Great dane
Standard poodle
Bernese
Labrador retriever (2)
Mix, mastiff/boxer
King Charles cavalier spaniel
Mix, samoyed/collie
Sheltie
OLA 6.05 28 German shepherd 6:4 4:4:2
Barbet
Standard poodle
Bernese
Labrador retriever (2)
a
Mean age of dogs on week 0 of research trial; units = ye ars.
b
Mean body weight of dogs on week 0 of research trial; units = kilograms.
BW, body weight; CAM, camelina oil; FLX, flaxsee d oil; OLA, canola oil.
Treatment oils were provided at an inclusion level of 8.2 grams of oil per 100 grams total dietary intake.
breed participated in this study (
Table 1). All dogs were deemed
healthy based on their previous medic al history as well as a pre-
study physical examination performed by a licensed veterinarian,
complete blood count (CBC), and serum biochemistry profile.
During the recruitment process, dogs were excluded if they had
any skin conditions, received any pro- or anti-inflammatory
medications 2-months prior to baseline samples, had abnormalities
on their physical examination, CBC, or serum biochemistry, or
were younger than 2 years of age. Dogs were housed at their
owners’ homes for the duration of the study, they followed their
usual daily routines. Pet owners were instructed to provide no
supplements, medications, antibiotics, antifungals, antiparasitics,
or topical creams without notifying the researchers. Prior to week
10, dog #10, consuming FLX, withdrew from the study due to
circumstances unrelated to the research trial or treatment diet.
Dietary treatments
Over a 4-week wash-in period, all dogs were acclimated to a
dry extruded commercial kibble (SUMMIT Three Meat Reduced
Calorie Recipe, Petcurean, Chilliwack, BC, Canada;
Table 2),
sunflower oil (SA Kernel-Trade, Kuiv, Ukraine;
Table 3), and beef-
based treats (Beef Tendersticks, The Crump Group, Brampton, ON,
Canada; proximate analysis: metabolizable energy 3039 kcal/kg;
crude protein minimum 65%; crude fat minimum 5.1%; crude fiber
maximum 4.0%; moisture max 9.56%). Oil was included in the diet
at 8.2 grams of oil per 100 grams of total food int ake, bringing the
total dietary lipid content to 20% on an as-fed basis. Treats were
included in the diet up to 2.5 grams per 100 grams total intake, and
the remaining proportion of the diet was provided as kibble. During
the wash-in period and throughout the study, daily portions of
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Richards et al. 10.3389/fvets.2023.1085890
food, oil, and treats were pre-weighed by researchers and provided
to the owners in 2-week intervals to be offered to dogs daily at a
frequency determined by the owner. To avoid the occurrence of
lipid peroxidation, owners were instructed to mix the oil with the
food immediately before feeding. Any leftover kibble, oil, and/or
treats were returned to researchers and subsequently weighed
and recorded. Dogs were initially fed to meet their estimated
maintenance energy requirements (110 kcal ME × kg BW
0.75
), and
BW was recorded every 2 weeks starting at baseline. Each dog’s food
allotment was then adjusted accordingly to maintain baseline BW
throughout the study. No abnormal observations were reported
by owners throughout the 16-week study period in terms of diet
tolerance (i.e., vomiting, stool quality, halitosis, etc.).
TABLE 2 Proximate analysis, metabolizable energy, omega-6 and
omega-3, and linoleic and docosahexaenoic acid content of a commercial
extruded kibble
a
on an as-fed basis, fed to 30 client-owned dogs during a
skin and coat health trial over a 16-week period.
Nutrient profile As fed basis
Moisture (%) 8.00
Crude protein (%) 21.0
Nitrogen-free extract (%) 52.0
Crude fiber (%) 2.80
Crude fat (%) 9.00
Omega 6 (%) 2.00
Omega 3 (%) 0.20
Linoleic acid (%) 1.90
Docosahexaenoic acid (%) 0.01
Ash (%) 7.10
Metabolizable energy (kcal/kg) 3,324
a
Chicken meal, whole brown rice, whole white rice, barley, oatmeal, chicken fat (preserved
with mixed tocopherols), peas, lamb meal, salmon meal, natural chicken flavor, whole dried
egg, sunflower oil, rice bran, flaxseed, dried kelp, dicalcium phosphate, potassium chloride,
choline chloride, sodium chloride, calcium carbonate, vitamins (vitamin A supplement,
vitamin D3 supplement, vitamin E supplement, niacin, L-ascorbyl-2- polyphosphate (a source
of vitamin C), d-calcium pantothenate, thiamine mononitrate, beta-carotene, riboflavin,
pyridoxine hydrochloride, folic acid, biotin , vitamin B12 supplement), minerals (zinc
proteinate, iron proteinate, copper proteinate, zinc oxide, manganese proteinate, copper
sulfate, ferrous sulfate, calcium iodate, manganous oxide, selenium yeast), DL-methionine,
glucosamine hydrochloride, chondroitin sulfate, yeast extract, Yucca schidigera extract,
dried rosemary.
Study design
This study was conducted using a randomized complete block
design (RCBD) with repeated measures. Following the 4-week
wash-in period, dogs were blocked by breed, age, and BW and
groups were randomly assigned to one of 3 treatment oils: camelina
oil (CAM) (n = 10; eight females; two males), flaxseed oil (FLX) (n
= 10; five females; five males), or canola oil (OLA) (n = 10; four
females; six males). The sunflower oil used during the wash-in was
replaced with either CAM, FLX, or OL A, and feeding continued as
described for 16 weeks. Both OLA and FLX were chosen as control
groups for t his study as they are commonly used to formulate
canine diets and provide a source of n-3 FAs.
Blood collection
Dogs were fasted for a minimum of 10 h overnight and blood
samples were collected via cephalic venipuncture using a syringe
(Becton, Dickinson and Company, Franklin Lakes, NJ, USA). Of
the collected blood, 5 mL was put into a serum vacutainer (Becton,
Dickinson and Company, Franklin Lakes, NJ, USA). Blood was
allowed to clot and was centrifuged at 7,200× g for 15 min using an
accuSpin Micro 17 centrifuge (Thermo Fisher Scientific, Waltham,
MA, USA). Then, the serum aliquots were frozen at −80
◦
C until
later analysis.
Inflammatory and oxidative markers
Serum samples were analyzed for prostaglandin E
2
(PGE
2
)
(Canine Prostaglandin E
2
ELISA Kit MBS013017, MyBioSource,
Vancouver, BC) and junction plakoglobin (JUP) (Canine
Junction Plakoglobin ELISA Kit MBS104997, MyBioSource,
Vancouver, BC) using commercially available ELISA (Enzyme-
linked immunosorbent assay) kits. Samples were run in
duplicate according to the manuf acturer’s instructions. Serum
glycosaminoglycan (GAG) (dimethyl methylene blue) and nitric
oxide (NO) (Griess Reaction; Molecular Probes, Eugene, OR)
concentrations were determined using spectrophotometric assays
(
26, 27). Serum NO and GAG samples were analyzed as previously
described by MacNicol et al. (
28).
TABLE 3 Analyzed fatty acid profiles of camelina oil, canola oil, flax oil, and sunflower oil fed to 30 client-owned dogs top dressed on commercial kibble
during a skin and coat health trial over a 16-week feeding period.
Parameter Sunflower
a
Canola
b
Flaxseed
b
Camelina
b
Saturated fatty acids (%) 9.61 6.50 8.20 9.50
Monounsaturated fatty acids (%) 14.1 63.8 16.6 35.2
Polyunsaturated fatty acids (%) 76.3 29.7 75.2 55.3
Omega 6 (%) 76.2 18.6 16.5 19.8
Omega 3 (%) 0.04 11.1 58.6 35.4
a
Numerical values from Kostik et al. (
25) and only represent generic sunflower oil, not the brand used for this study.
b
Samples analyzed in duplicate by SGS Canada Inc. (Guelph, ON, Canad a), average values reported.
Burron et al. (
24).
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Skin barrier function
Skin barrier function and integrity were assessed by measuring
TEWL, which is defined as the amount of water that passively
evaporates through skin to the external environment due to a
water vapor pressure gradient on both sides of the skin barrier
and is commonly used to characterize skin barrier function and
integrity (
29, 30). On weeks 0, 2, 4, 10, and 16, TEWL was
measured using a VapoMeter
R
SWL-3 (Delfin Technologies Ltd,
Kuopio, Finland), according to the manufacturer’s instructions.
Since privately-owned dogs were used, it was not fe asible to
shave multiple patches for TEWL measurements, and as a result,
researchers chose three body sites with little hair to measure TEWL,
including: the right paw pad, right pinna, and right inner thigh. Ten
measurements were taken per body site and the average was used
for analyses. Once the averages were calculated, any values above or
below the average by 50 g/m
2
/h or more were considered outliers
and removed. All dogs were brought to the University of Guelph by
their owners on collection days to ensure environmental conditions
during collections remained consistent. All measurements were
carried out by a single operator, in the same order of body sites,
and in a climate-controlled room to maintain consistency between
samples and to avoid variation in VapoMeter
R
readings due to
temperature and humidity fluctuations (
29). Room conditions
were stable at 22–23
◦
C ambient temperature and 44–50% ambient
relative humidity. The evaporation rate value is calculated in
grams of water per square meter per hour (g/m
2
/h). All dogs
were behaviorally acclimated to the use of the VapoMeter
R
, the
researchers involved in sample collection, and the collection room,
prior to the first sample day to minimize stress, thereby reducing
variation in measurements. If dogs were wet due to we ather upon
arrival they were dried with a towel, to reduce variation further.
Coat quality
Two researchers blinded to treatment were trained to perform
a subjective coat assessment on weeks 0, 2, 4, 10, and 16 using
a 5-point Likert scale (under
Supplementary material). A Likert
scale was used to measure the softness, shedding, dander, shine,
spring, softness uniformity, color, color uniformity, and follicle
density of the coat. Follicle density was assessed on the center
of the back of the dogs by scoring the thickness/amount of hair
coming from individual follicles. To increase consistency among
dogs given different management practices in each household, all
dogs were bathed 2 weeks prior to each assessment and owners were
instructed to keep dogs dry and to not brush or groom them during
this period.
Statistical analysis
Data are presented as mean ± SD unless otherwise stated. All
statistical analyses were performed using the PROC GLIMMIX
of SAS Studio
R
software (v.9.4., SAS Institute Inc., Cary, NC,
USA). Dog was the experimental unit, and treatment, TEWL site,
and sex, and age were treated as fixed effects (age and sex data
not presented). Week was treated as a repeated measure. An
analysis of variance (ANOVA) was performed to assess the effects of
treatment on inflammatory and oxidative marker concentrations,
TEWL, and coat scores. When the fixed effects were significant,
the means were separated using Tukey–Kramer adjustments.
Significance was declared at a P ≤ 0.05. Trends were declared at
P ≤ 0.10.
Results
Inflammatory and oxidative markers
Prostaglandin E
2
There were no differences among treatments (P = 0.973), across
weeks (P = 0.397), or for treatment by week interactions (P =
0.987) (
Table 4). Additionally, no differences were observed due to
sex (P = 0.937) or age (P = 0.274).
Junction plakoglobin
There were no differences among treatments (P = 0.969), across
weeks (P = 0.249), or for treatment by week interactions (P =
0.913) (
Table 4). No differences were observed due to sex (P =
0.914) or age (P = 0.743).
Glycosaminoglycan
There were no differences among treatments (P = 0.208), across
weeks (P = 0.995), or for treatment by week interactions (P =
0.915) (
Table 4). Concentrations of GAG tended to be greater in
males compared to females (P = 0.078). There were no differences
obser ved due to age (P = 0.329).
Nitric oxide
There were no differences among treatments (P = 0.648), across
weeks (P = 0.359), or for treatment by week interactions (P =
0.729) (
Table 4). No differences were observed due to sex (P =
0.226) or age (P = 0.424).
Transepidermal water loss
Of the 4,440 individual TEWL measurements collected
throughout the study period, 18 were considered outliers and
removed [D = Dog, W = Week; Paw pad: D6W2(CAM),
D8W16(FLX)(2 values), D9W16(FLX), D17W4(CAM), D18W2
(FLX), D18W4(FLX)(2 values), D23W10(CAM), D23W16(CAM);
Inner ear: D5W4(OLA), D5W10(OLA), D12W10(OLA); Inner
leg: D6W2(CAM), D6W10(CAM), D12W0(OLA), D16W0(FLX),
D29W0(FLX)]. These outliers could often be attributed to changes
in the environment, leading to signs of stress or excitement in
the dogs (i.e., researchers entering and leaving the room, noises
occurring outside of the sample room, and in the case of some
outliers these samples were taken near the end of the collection
period and the dogs would become impatient, no longer wanting
to remain in the same spot for samples).
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Richards et al. 10.3389/fvets.2023.1085890
TABLE 4 Serum prostaglandin E
2
, junction plakoglobin, glycosaminoglycan, and nitric oxide concentrations of healthy adult dogs supplemented one of
three treatment oils
a
on weeks 0, 2, 4, 10, and 16 of a skin and coat health trial, presented as lsmeans ± standard error.
Week P-values
0 2 4 10 16 Treatment Week Treatment
∗
week
Prostaglandin E
2
(pg/mL)
CAM 0.88 ± 1.45 2.77 ± 1.45 3.49 ± 1.45 2.35 ± 1.45 2.32 ± 2.33
OLA 3.07 ± 1.34 3.07 ± 1.38 2.41 ± 1.44 2.82 ± 1.44 2.80 ± 1.39 0.9734 0.3965 0.9868
FLX
2.55 ± 1.23 4.07 ± 1.28 3.07 ± 1.34 3.44 ± 1.28 3.15 ± 1.33
Junction plakoglobin (ng/mL)
CAM 8.73 ± 1.08 9.38 ± 1.08 8.56 ± 1.11 8.65 ± 1.08 7.82 ± 1.08
OLA 10.09 ± 1.01 9.60 ± 1.01 9.51 ± 1.01 9.96 ± 1.01 7.39 ± 1.09 0.9693 0.2487 0.9133
FLX
8.94 ± 0.94 10.97 ± 0.94 10.78 ± 0.94 9.34 ± 0.97 8.35 ± 1.02
Glycosaminoglycan (µg/mL)
CAM 4.43 ± 0.73 4.73 ± 0.73 4.23 ± 0.73 4.91 ± 0.80 3.97 ± 0.76
OLA 3.03 ± 0.73 4.34 ± 0.73 4.47 ± 0.72 4.17 ± 0.76 3.74 ± 0.72 0.2083 0.9945 0.9147
FLX
4.33 ± 0.66 4.50 ± 0.66 4.82 ± 0.69 4.85 ± 0.69 4.04 ± 0.78
Nitric oxide (µM/mL)
CAM 2.20 ± 5.50 9.30 ± 5.50 4.82 ± 5.62 8.34 ± 5.60 10.90 ± 5.64
OLA 4.31 ± 5.05 7.19 ± 5.05 5.85 ± 5.05 9.26 ± 5.05 10.15 ± 5.18 0.6476 0.3587 0.7288
FLX
11.70 ± 4.58 12.76 ± 4.58 19. 56 ± 4.72 13.74 ± 4.72 16.34 ± 4.72
a
Treatment oils: CAM, Camelina; OLA, Canola; FLX, Flaxseed oil; Data presented as mean ± stan d ard error; n for each tre a tment group on weeks 0, 2, 4: CAM = 10, OLA = 10, FLX = 10, and
weeks 10, 16: CAM = 10, OLA = 10, F LX = 9.
TABLE 5 Mean transepidermal water loss (TEWL) values (g/m
2
/h) of the right paw pad, right pinna, and right inner thigh of healthy adult dogs
supplemented one of three treatment oils
a
on weeks 0, 2, 4, 10, and 16 of a skin and coat health trial, presented as lsmeans ± standard error.
Week P-values
Treatment Site 0 2 4 10 16 Trt Site Week
CAM Paw pad 92.57 ± 8.80 98.97 ± 8.80 88.28 ± 8.80 83.98 ± 8.80 92.7 ± 8.80
OLA Paw pad 88.27 ± 8.85 86.95 ± 8.85 76.32 ± 8.85 71.38 ± 8.85 67.56 ± 8.85
FLAX Paw pad 99.43 ± 8.79 109.51 ± 8.79 100. 37 ± 8.79 87.38 ± 9.21 88.46 ± 9.21
CAM Pinna 14.03 ± 8.80 12.27 ± 8.80 18.78 ± 8.80 14.47 ± 8.80 16.68 ± 8.80
OLA Pinna 14.43 ± 8.85 15.84 ± 8.85 16.87 ± 8.85 24.43 ± 8.85 18.40 ± 8.85 0.7261 <0.0001 0.7375
FLAX
Pinna 9.10 ± 8.79 12.69 ± 8.79 12.13 ± 8.79 13.27 ± 9.21 9.92 ± 9.21
CAM Inner thigh 23.11 ± 8.80 23.56 ± 8.80 18.2 ± 8.80 17.52 ± 8.80 22.93 ± 8.80
OLA Inner thigh 16.86 ± 8.85 15.72 ± 8.85 18.18 ± 8.85 17.32 ± 8.85 21.23 ± 8.85
FLAX Inner thigh 15.7 ± 8.79 13.44 ± 8.79 16.36 ± 8.79 14.30 ± 9.21 16.51 ± 9.21
a
Treatment oils: CAM, Camelina; OLA, Canola; FLX, Flaxseed oil; Data presented as mean ± stan d ard error; n for each tre a tment group on weeks 0, 2, 4: CAM = 10, OLA = 10, FLX = 10, and
weeks 10, 16: CAM = 10, OLA = 10, F LX = 9.
There were no differences among treatments (P = 0.726), across
weeks (P = 0.738), or for treatment by week interactions (P =
0.996). Additionally, there were no differences for site by week
(P = 0.378), or sex (P = 0.274) (
Table 5). However, there were
differences observed among sites (P < 0.0001), in that TEWL values
for the paw pad were greater than those of the pinna or inner thigh.
Additionally, there was a trend observed in age (P = 0.072), in that
senior dogs (11–14 years; n = 3) tended to have lower mean TEWL
values compared to young (2–4 years; n = 7), young adult (5–7
years; n = 9), and adult dogs (8–10 years; n = 9).
Coat quality
Softness
There were no differences among treatments (P = 0.539), for
treatment by week interactions (P = 0.757), or due to age (P =
0.479), week by age (0.338) or week by sex (P = 0.738) interactions.
However, there were differences observed across weeks for pooled
data (P = 0.005) in that softness was greater on week 10 and
16 compared to week 0, and greater on week 10 compared to
week 2. Week 4 was not different from any other time points
Frontiers in Veterinary Science 06 frontiersin.org
Richards et al. 10.3389/fvets.2023.1085890
FIGURE 1
Mean coat quality assessment scores completed using a 5-point Likert scale on 30 client owned healthy adult dogs fed one of three treatment oils
(camelina oil, canola oil, flaxseed oil) and commercial ki bble.
A,B,C,D
Bars without a common letter dier significantly (P < 0.05).
(Figure 1). Additionally, softness was greater in females compared
to males (P = 0.026).
Shedding
There were no differences among treatments (P = 0.882), due to
age (0.894) or sex (P = 0.760), or for treatment by week (P = 0.444),
week by age (P = 0.302), or week by sex (P = 0.514) interactions.
For pooled data across weeks, shedding was greater on weeks 0
and 2 compared to weeks 10 and 16 (P = 0.004). Week 4 was not
different from any other time points (
Figure 1).
Dander
There were no differences among treatments (P = 0.648), due
to age (P = 0.114) or sex (P = 0.349), across weeks (P = 0.129),
or for treatment by week (P = 0.869), week by age (P = 0.171), or
week by sex (P = 0.163) interactions (Figure 1).
Shine
There were no differences among treatments (P = 0.815), due
to age (P = 0.945), or sex (P = 0.191), or treatment by week (P =
0.998), week by age (0.992), or week by sex (P = 0.375) interactions.
However, there were differences across weeks for pooled data (P <
0.0001) in t hat shine on weeks 2, 4, 10, and 16 was greater than at
week 0 (
Figure 1).
Spring
There were no differences among treatments (P = 0.918), due
to age (P = 0.663) or sex (P = 0.401), or for treatment by week
(P = 0.397), week by age (P = 0.773), or week by sex (P =
0.997) interactions. However, there were differences across weeks
for pooled data (P = 0.014) in t hat spring was greater on week 10
compared to week 4 and 0. There were no differences on weeks 2
and 16 (
Figure 1).
Softness uniformity
There were no differences among treatments (P = 0.969), due
to age (P = 0.860) or sex (P = 0.132), or for treatment by week
(P = 0.799), week by age (P = 0.996), or week by sex (P =
0.142) interactions. However, a trend was observed across weeks
for pooled data (P = 0.065) in that softness uniformity tended to be
greater on week 16 compared to week 0. Weeks 2, 4, and 10 were
not different from any other time points (
Figure 1).
Fur color
There were no differences among treatments (P = 0.323), due
to age (P = 0.770) or sex (P = 0.546), or for treatment by week
(P = 0.567), week by age (P = 0.345), or week by sex (P =
0.954) interactions. However, there were differences across weeks
for pooled data (P < 0.0001) in t hat color was higher on weeks 4,
10, and 16 compared to week 0. Additionally, color was greater on
week 10 and 16 compared to week 2. Furthermore, color tended to
be higher on week 10 compared to week 4 (
Figure 1).
Fur color uniformity
There were no differences among treatments (P = 0.541), due
to age (P = 0.893) or sex (P = 0.911), across weeks (P = 0.362),
or for treatment by week (P = 0.291), week by age (P = 0.787), or
week by sex (P = 0.910) interactions (
Figure 1).
Follicle density
There were no differences among treatments (P = 0.873), due
to age (P = 0.795) or sex (P = 0.854), or for treatment by week
Frontiers in Veterinary Science 07 frontiersin.org
Richards et al. 10.3389/fvets.2023.1085890
(P = 0.670), week by age (P = 0.846), or week by sex (P =
0.299) interactions. However, there were differences across weeks
for pooled d ata (P = 0.027) in that follicle density was greater on
week 16 compared to week 0. Weeks 2, 4, and 10 were not different
from any other time points (Figure 1).
Discussion
The purpose of this study was to assess the effects of camelina
oil supplementation on skin and coat health compared to canola
and flaxseed oil, two oils currently used to formulate canine diets.
The results presented herein suggest no differences in TEWL, coat
quality, or the inflammatory and oxidative markers assessed due to
treatment over the 16-week period.
Inflammatory and oxidative markers
In the current study, concentrations of GAG tended to be
higher in males compared to females. Studies in humans by
(1) Larking (
31) and (2) Claassen and Werner (32) found that,
similar to the present study, females have lower concentrations
of GAG. Claassen and Werner analyzed GAG in thyroid cartilage
while Larking measured GAG excretion in the tissue. Since
GAG is a marker of cartilage turnover, Claassen and Werner
attribute their findings to greater cartilage turnover in males,
while Larking accredits their findings to the males in their study
having a greater mean height (
31, 32). It is possible that the
female dogs in the present experiment had a smaller average
height and lower cartilage mineralization than the males, which
contributed to the lower concentration of circulating GAGs
obser ved. However, height and cartilage mineralization were not
measured in the present study. Furthermore, the observation
made in our study was only a tendency; this, combined with
the dearth of work carried out in dogs and lack of equal
distribution of male/female, intact/neutered/spayed dogs in the
current study make it difficult to form any cogent conclusions.
Future research should investigate this relationship further using
a dog model.
No significant changes were observed in PGE
2
, JUP, GAG,
or NO concentrations over the 16-week study period. It is
possible that the stability of these concentrations across time and
among treatments is attributed to the lack of exercise or immune
challenge experienced by the dogs on the current study. It is well-
established that both exercise and immune challenges result in
a wide range of physiological and biochemical adaptations, the
magnitude of which is directly related to the intensity and duration
of the exercise or immune challenge encountered (
33–36). This
wide range of physiological and biochemical adaptations include
changes in inflammatory and oxidative biomarker concentrations
(
28, 33).
Dogs and horses both experience increased PGE
2
concentrations following exercise. In horses, NO and GAG
concentrations increase following exercise and compared to
baseline, but no change was observed in dogs (
28, 33). Pearson
et al. attribute these results, similar to previous findings, to
variations in NO production depending on exercise intensity,
suggesting that it is possible that the lack of changes observed in
NO concentration in the current study is due to the low intensity
of the exercise experienced by the dogs (
33). Markers like PGE
2
,
NO, GAG, and JUP are often upregulated during times of immune
challenge/disease (
37–40). A myriad of studies completed in
humans suggest no effects of n-3 PUFA supplementation on
inflammatory or immune markers in healthy individuals (
41–43).
As an example, Pot et al. found that supplementing fish oil and
sunflower oil to healthy individuals had no effect on chemokine,
cytokine, or cell adhesion molecule concentration compared to
baseline (
41). Healthy individuals, similar to the canine subjects
of our study, generally have low levels of circulating inflammatory
markers. Thus, the chance that low levels of inflammation are
reduced even further by an intervention with oil is very small
and difficult to measure. The dogs of the present study were
healthy upon recruitment and on every sample period based
on a veterinary examination, as well as CBC and biochemistry
analysis, indicating a lack of immune response that would elicit an
inflammatory response. Additionally, the dogs did not participate
in any intense exercise prior to or on sample days, and thus had
no known reason to elicit any exercise stress induced response
impacting markers of inflammatory or oxidative stress. For safety
and animal care purposes, no procedures with the potential to
cause harm to the animals, like an inflammatory or immune
challenge, can be carried out in client-owned dogs. Additionally,
the objective of the present study was to determine how these
three oils compare to one another in terms of their effe cts on these
biomarkers to gauge their use in dog food formulations for typical
pets, not to evaluate their performance following an exercise or
immune challenge. Future studies should compare the effects
of these three oils and their performance following exercise and
immune challenge.
Transepidermal water loss
In the present study, mean TEWL values were significantly
greater when measured on the paw pad compared to the inner leg
and inner ear. This is likely the result of the tubular, unbranched
eccrine glands that open directly onto the skin of the paw pads
and noses of canines. These glands allow sweat to be released
from these areas, contributing to the water-loss detected by the
VapoMeter, and thereby likely contributing to greater TEWL values
compared to the inner leg and pinna (
44). Additionally, TEWL
values were found to be lower in senior dogs compared to young,
young adult, and adult dogs. Similar findings have been observed in
other canine and human studies and although the exact mechanism
behind these observations is unclear, there are various theories
(
45, 46). The thickness of the stratum corneum and flattening of
corneocytes increases with age, while natural moisturizing f actors,
stratum corneum hydration, and epidermal lipid synthesis are
reduced (
47–53). Additionally, the density of dermal capillaries
decreases with age, which may lower skin temperature and in
turn decrease water diffusion (
51, 54). All of these findings
provide examples of mechanisms that increase the path length
and resistance of a water mole cule and subsequently contribute
to lower TEWL in older individuals, and in agreement with the
present study.
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Richards et al. 10.3389/fvets.2023.1085890
Coat quality
Spring and follicle density increased significantly from baseline.
This is likely due, at least in part, to the growth of winter coats as
the study began at the end of summer and went into the winter
(September–January). Dogs have a light summer undercoat that is
shed before a thick winter undercoat grows in, which could explain
the increase in spring and follicle density. This further supports t he
obser vation of the present study in that shedding was greater in all
dogs at the beginning of the study at weeks 0 and 2, compared to
weeks 10 and 16.
Softness, shine, and color of the dogs’ coats increased from
baseline. This is likely a result of the dogs consuming an increased
amount of n-3 FAs following baseline, which can be further
metabolized into EPA and DHA, though with limited efficiency.
Supplementation of fish oil, a rich source of EPA and DHA,
was found to improve skin and hair coat quality in dogs from
baseline based on a clinical score, with maximal improvement
occurring after 8 weeks (
55). The positive effects on skin and
coat health are thought to be due to an increase in EPA and
DHA in the erythrocyte membrane, along with increased total
lipids in the hair shaft (
55). The same study observed that
following supplement withdrawal, skin and coat health clinical
scores remained the same for 1 month and began to deteriorate
following the second month (
55). Although we did not take
measurements on week 8, we did take measurements on week
10, and this is where we saw the largest improvement (i.e.,
softness, shedding, shine, spring, and color). This is most likely
due to the increase in ALA, which is the parent compound
of EPA and DHA, the dogs received from their treatment oil
(CAM 1:1.8, FLX 1:4.19, OLA 1:0.59) in comparison to the
wash-in sunflower oil (1:0). It is important to note that our
study had no negative control group, since the absence of an
oil supplement would alter all macronutrient intakes and our
aim was to compare to existing approved oil supplements. As
a result it cannot be ruled out that the observed changes
in coat quality may be a result of the placebo effect. Future
studies should consider employing a control group fed no oil
supplement to rule out the possibility of the placebo effect
impacting observations.
All dogs in the current study were considered healthy,
with no known dermatological conditions or skin disorders.
The coats of these dogs were in relatively good condition
at baseline, and future research should investigate these oil
supplements and their effects on skin and coat health in dogs
with poor skin and coat quality as a result of conditions like
atopic dermatitis. It is important to note that ectoparasites,
particularly fleas in dogs, can negatively impact skin and coat
health (
56). In this study, although complete blood count and
biochemistry values were assessed, and physical examinations were
performed by a licensed veterinarian prior to study recruitment
and throughout the entire trial, diagnostic and preventive control
in terms of ectoparasites was not considered, and this is a
limitation of this study. Authors recommend future studies
consider using more specific techniques as inclusion criteria
when recruiting participants in order to ensure the absence and
prevention of parasites and their potential impact on skin and
coat health.
Conclusion
In conclusion, camelina oil is comparable to canola and flaxseed
oil in terms of its effects on skin barrier function, coat quality,
and the circulating inflammatory and oxidative markers measured
in the current study when fed to healthy adult dogs, subjected
to no physical or immunological challenge, and observed for 16-
weeks. Canola and flaxseed oil are commonly used in canine food
formulations. Flaxseed oil specifically has the ability to support skin
and coat health claims, making camelina oil a potential alternative
plant-based oil source with high concentrations of ALA that could
contribute to achieving the ideal n-6:n-3 ratio in canine diets, while
supporting skin and coat health claims.
Data availability statement
The raw data supporting the conclusions of this article will be
made available by the authors, without undue reservation.
Ethics statement
The animal study was reviewed and approved by University of
Guelph Animal Care Committee. Written informed consent was
obtained from the owners for the participation of their animals in
this study.
Author contributions
AS and WP: conceptualization and funding acquisition. AS,
WP, and DM: methodology. TR, SB, KP, and CG: study conduct.
TR: formal analysis and writing—original draft preparation. TR,
SB, DWM, CG, KP, LT, DM, WP, and AS: writing—reviewing and
editing. All authors have read and agreed to the published version of
the manuscript. All authors contributed to the article and approved
the submitted version.
Funding
This project was funded by the Canadian Agricultural
Partnership program as part of the diverse field crops clusters and
funding from with Smart Earth Camelina. The kibble was provided
by Petcurean, and the treats were provided by Crumps’ Naturals.
Acknowledgments
Authors would like to thank the undergraduate and graduate
students who assisted with this project, and all of the dogs and their
owners for their commitment and cooperation during this study.
Conflict of interest
AS is the Champion Petfoods Chair in Canine and Feline
Nutrition, Physiology and Metabolism and additionally consults
for C hampion Petfoods. AS has received various honoraria
Frontiers in Veterinary Science 09 frontiersin.org
Richards et al. 10.3389/fvets.2023.1085890
and research funding from various pet food manufacturers and
ingredient suppliers and was a former employee of P&G Petcare
and Mars Petcare.
The remaining authors declare that the research was conducted
in the absence of any commercial or financial relationships that
could be construed as a potential conflict of interest.
Publisher’s note
All claims expressed in this article are solely those
of the authors and do not necessarily represent those of
their affiliated organizations, or those of the publisher,
the editors and the reviewers. Any product that may
be evaluated in this article, or claim that may be made
by its manufacturer, is not guaranteed or endorsed by
the publisher.
Supplementary material
The Supplementary Material for this article can be found
online at:
https://www.frontiersin.org/articles/10.3389/fvets.2023.
1085890/full#supplementary-material
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