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An experimental meat-free diet maintained haematological characteristics
in sprint-racing sled dogs
Wendy Y. Brown
1
*, Barbara A. Vanselow
2
, Andrew J. Redman
3
and John R. Pluske
4
1
Animal Science, School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia
2
NSW Department of Primary Industries, Beef Industry Centre, University of New England, Armidale, NSW 2351, Australia
3
Mars Petcare Australia, Petcare Place, Wodonga, Vic 3690, Australia
4
School of Veterinary and Biomedical Sciences, Animal Research Institute, Murdoch University, Murdoch, WA 6150, Australia
(Received 2 December 2008 – Revised 19 April 2009 – Accepted 27 April 2009 – First published online 1 June 2009)
A dog’s nutrient requirements can theoretically be met from a properly balanced meat-free diet; however, proof for this is lacking. Exercise places
additional demands on the body, and dogs fed a meat-free diet may be at increased risk of developing sports anaemia. We hypothesised that
exercising dogs would remain in good health and not develop anaemia when fed a nutritionally balanced meat-free diet. To this end, twelve
sprint-racing Siberian huskies were fed either a commercial diet recommended for active dogs (n6), or a meat-free diet formulated to the
same nutrient specifications (n6). The commercial diet contained 43 % poultry meal, whereas soyabean meal and maize gluten made up 43 %
of the meat-free diet, as the main protein ingredients. Dogs were fed these diets as their sole nutrient intake for 16 weeks, including 10 weeks
of competitive racing. Blood samples were collected at weeks 0, 3, 8 and 16, and veterinary health checks were conducted at weeks 0, 8 and 16.
Haematology results for all dogs, irrespective of diet, were within normal range throughout the study and the consulting veterinarian assessed all
dogs to be in excellent physical condition. No dogs in the present study developed anaemia. On the contrary, erythrocyte counts and Hb values
increased significantly over time (P,0·01) in both groups of dogs. The present study is the first to demonstrate that a carefully balanced meat-free
diet can maintain normal haematological values in exercising dogs.
Sled dogs: Exercise: Vegetarian diet: Blood count
There has been a steady increase in the number of articles on
vegetarian nutrition in humans appearing in the biomedical
literature, and this has been attributed to the increased popu-
larity of vegetarianism
(1)
and the documented health benefits
associated with well-balanced vegetarian diets
(2)
. In contrast
to this, there is a dearth of research into vegetarian nutrition
in the canine. In this regard, some dog and cat owners wish
to feed their pets a totally meat-free diet
(3)
for the same ethical
reasons that they themselves are vegetarian
(4)
. However, none
of the currently available meat-free dog and cat foods base
their claims of nutritional adequacy on recognised feeding
protocols, such as those specified by the Association of
American Feed Control Officials (AAFCO)
(5)
. Furthermore,
an independent analysis of two commercial vegan diets for
cats, claiming to be nutritionally complete and balanced,
found the diets to have multiple nutrient deficiencies
(6)
.
Unlike the obligatory carnivorous cat, dogs can synthesise
nutrients such as taurine and vitamin A
(7)
and theoretically
it is possible for the dog to subsist on a diet based solely on
plant ingredients. Commercial dry dog foods typically contain
a high proportion of plant ingredients, as a high grain content
is necessary for successful extrusion
(8)
. It is only a small step
from some of the popular cereal-based dry dog foods to one
that contains no meat at all. Conceptually, however, the gap
is much larger, and demonstrating that a meat-free diet is ade-
quate in sedentary dogs will not change the perception of
many dog owners that meat is required for dogs that are
actively working, or racing
(9)
. For this reason, sprint-racing
sled dogs were chosen for our experiment to challenge the
concept that meat is an essential dietary ingredient for exercis-
ing dogs. Our aim was to develop a nutritionally adequate
meat-free diet, based on chemical analysis, and to demonstrate
nutritional adequacy by feeding the diet in a controlled exper-
iment to active dogs. We hypothesised that dogs would remain
in good health, based on veterinary health checks and haema-
tological characteristics, and not develop anaemia.
Experimental methods
Twelve pure-bred Siberian huskies participated in the study,
which ran from 24 May to 20 September 2004 to coincide
with the Australian sled-dog racing season. The experiment
was of 16 weeks’ duration, incorporating 2 weeks of pre-
race training, 10 weeks of competitive racing and 4 weeks
of recovery. Throughout the study, dogs were fed either the
experimental meat-free diet (n6) or the meat-based control
*Corresponding author: Dr Wendy Yvonne Brown, fax þ61 2 6773 3922, email wbrown@une.edu.au
Abbreviations: BW, body weight; CP, crude protein; Cr, creatine; ME, metabolisable energy; PCV, packed cell volume.
British Journal of Nutrition (2009), 102, 1318–1323 doi:10.1017/S0007114509389254
qThe Authors 2009
British Journal of Nutrition
diet (n6) as their sole nutrient intake. Blood samples (5 ml)
were collected from the cephalic vein of dogs at rest (0, 3, 8
and 16 weeks) and analysed for complete blood count using
an automated cell counter (CellDyn 3500R; Abbott Diagnos-
tics, North Ryde, NSW, Australia). Veterinary health checks
were performed at weeks 0, 8 and 16 by the dog owners’
usual veterinarian, who was blinded to the dietary treatments.
Veterinary health checks consisted of a full physical examin-
ation, auscultation of the heart and lungs, and measurement of
rectal temperatures. Authority to conduct the present study
was granted by the University of New England Animal
Ethics Committee, in accordance with section 25 of the
Animal Research Act (1985).
Animal management
For the duration of the study, dogs were maintained in their
usual environment (Malusky Kennels, Belford, NSW, Austra-
lia), kennelled in pairs, with free access to water at all times.
Dogs were always kennelled with another dog from the same
dietary group to remove any likelihood of dogs accessing the
wrong diet. Each dog had its own bed, and kennels were fully
covered and protected from the weather. A large outdoor
grassed enclosure provided additional social interaction
where dogs were placed twice per d, as a single group,
under the owners’ supervision. The temperature in the kennels
ranged from 258Cto278C over the study period.
At 6 weeks before commencing the experiment, dogs were
administered booster vaccinations against canine distemper,
hepatitis and parvovirus (Canvace3; CSL, Parkville, Vic,
Australia) by subcutaneous injection. Dogs were weighed
and treated orally with anthelmintic (Drontal
w
Allwormer
w
;
Bayer Australia Ltd, Pymble, NSW, Australia) worming
tablets (active ingredients: praziquantel, 50 mg; pyrantel
embonate, 49·8 mg; febantel, 250 mg) at the recommended
dose rate (one tablet per 10 kg body weight (BW)) at week
0 and again at week 5.
Diets and feeding
Two diets were compared in the present study, a meat-based
and a meat-free diet of similar nutrient composition
(Tables 1 and 2). The meat-based diet was a commercial
dog food recommended for active dogs (Pedigree
w
Advancee
Energy – chicken; Mars Petcare Australia, Raglan, NSW,
Australia) and contained 43 % poultry meal (before extrusion)
as its main protein source. The experimental meat-free diet
(manufactured at the Mars Petcare pilot plant, Wodonga, Vic,
Australia) contained maize gluten and fine soya meal (passed
through a 1 mm sieve) as its main protein sources, which together
made up 43 % of the pre-extrusion ingredients. The meat-free diet
was coated with stabilised vegetable oil, whereas the meat-based
diet was coated with poultrytallow and poultry digest. A balanced
amino acid ratio was achieved in the meat-free diet without the use
of crystalline amino acids. Dogs were fed their allocated diets in
individual bowls as a single meal each evening, and this com-
prised their sole nutrient intake for the duration of the 16-week
experiment. Dogs were observed during feeding to confirm that
each individual consumed its allocated ration. Individual feed
intakes were recorded daily and BW were measured fortnightly.
Individual feeding levels were adjusted as necessary to maintain
ideal BW. Ideal BW were determined by the trainer and equated
to a body condition score of 4 using a standard nine-point scale
(Purina Body Condition System) ranging from 1 (emaciated) to
9 (severely obese).
As the meat-free diet had not been manufactured pre-
viously, a separate feeding trial was conducted to determine
digestibility coefficients of the experimental diet. For the
digestibility trial, eight dogs of mixed breeds were individu-
ally housed on concrete floors at the University of New
England Dog Research Facility. Following an adaptation
period, the experimental diet was fed solely for 12 d and
all faeces produced during the final 4 d were collected for
determination of total-tract apparent digestibility.
Exercise and racing schedule
Dogs were trained and raced in teams (a six-dog team, a four-
dog team, and a two-dog team) by their usual trainers. Within
teams, each dog was paired with another dog of similar ability,
based on the trainer’s assessment of performance before the
commencement of the trial. Each dog was harnessed to its
allocated exercise partner for all training and racing activities.
Within each exercise pair, one dog was allocated to diet 1 and
the other to diet 2, maintaining an even distribution for sex,
BW and age between the two dietary groups. Following allo-
cation of dogs into diet groups 1 and 2, the test diets were then
arbitrarily designated: the meat-free as diet 1 and meat-based
as diet 2. Each group comprised three female and three male
dogs; mean age and BW were 3·7 years and 19·7kg respect-
ively for dogs fed the meat-free diet and 3·2 years and
20·2 kg for dogs fed the meat-based diet. One dog from each
group was neutered; all others were entire.
Pre-race training commenced with the onset of cooler
weather in April, and involved dogs pulling heavily laden
carts at slow speed. The final 2 weeks of this phase of training
were included in the experiment, during which the dogs com-
pleted seven training runs of 6 km distances at an average
speed of 12 km/h. The next 10 weeks involved competitive
racing in addition to the training runs which continued three
or four times per week. The heavily weighted rigs were
replaced with light-weight rigs, and the training runs became
faster (20 km/h) and longer (6 –10 km runs). Dogs participated
in sprint races approximately once a fortnight, from 12 June
(week 2) until the 14 August (week 12). Sprint races were
run in accordance with Australian Sled-dog Sports Association
Table 1. Composition of diets before extrusion
Diet
Ingredient (g/kg) Meat-based Meat-free
Rice (broken) 120 120
Maize (whole) 170 250
Sorghum 140 –
Poultry meal 430 –
Maize gluten 60 300
Fine soya meal – 130
Sodium caseinate – 60
Vegetable mix – 60
Sugarbeet pulp 30 –
Vitamin and mineral mix 50 80
Meat-free diet sustains exercising dogs 1319
British Journal of Nutrition
(ASSA) rules, the maximum distance for a sprint race being
12 km for a team of six, 9 km for a team of four, and 2 km
for a team of two. Following the 10-week racing phase, train-
ing was gradually reduced over the 4-week recovery period.
Chemical analysis of diets
Representative samples of the two diets were finely ground
before chemical analyses. N content was determined using
an FP-2000 LECO Nitrogen Analyzer (LECO Corp.,
St Joseph, MO, USA), from which crude protein (CP) concen-
tration was calculated (CP ¼N£6·25). The gross energy of
the diets was determined with an IKA
w
-Werke C7000 bomb
calorimeter (IKA
w
Group, Staufen, Germany). The metabolis-
able energy (ME) content was calculated from digestible CP
and gross energy using a correction factor of 5023 kJ/g for
energy lost in urine
(5)
. Fat content was determined by Soxhlet
extraction with chloroform
(10)
. Total starch content was deter-
mined using the Megazyme Total Starch assay kit (Megazyme
Australia Pty, Warriewood, NSW, Australia). The NSP
content of the diets was determined by a combination
of the methods of Englyst & Hudson
(11)
and Theander &
Westerlund
(12)
. Amino acid analysis was conducted by the
Department of Primary Industries (Werribee, Vic, Australia).
The amino acids, apart from tryptophan, were assayed using
cation exchange chromatography following acid hydrolysis.
Methionine and cystine were first pre-oxidised with formic
acid before acid hydrolysis. Tryptophan was determined
by alkaline hydrolysis using a reverse-phase column with
UV detection at 280 nm. Mineral content was determined
using a Reagent-FreeeIon Chromatograph (ICS-2000 Ion
Chromatography System; Dionex Corp., Sunnyvale, CA,
USA) and AS40 Autosampler (Dionex Corp.).
Statistical methods
ANOVA for repeated measures was performed on haematolo-
gical data using the Super ANOVA statistical software pack-
age (Abacus Concepts, Berkley, CA, USA). Factors fitted to
the model were diet, time and their interaction. Duncan’s
new multiple-range test was used to separate the means
which differed significantly. Data are presented as mean
values with their standard errors. Haematological values
differed between the dietary groups at the commencement of
the study (week 0) for erythrocytes, Hb and packed cell
volume (PCV). To enable interpretation of the effect of diet
on these variables, values measured at week 0 for each dog
were subtracted from values measured at subsequent weeks
and these differences from the initial baseline values were
then subjected to statistical analysis.
Results
Both the meat-based and the meat-free diets were readily
consumed. Average daily nutrient intakes are presented in
Table 2. Based on chemical analyses, both of the diets fed
in the present study exceeded the recommended nutrient
requirements for maintenance in adult dogs
(13)
(Table 3).
All nutrients were within the known minimum and safe maxi-
mum upper limits. From the digestibility trial, DM, gross
energy, CP and starch digestibility for the meat-free diet
were: 83·1 (SEM 0·91), 87·5 (SEM 0·69), 89·4 (SEM 0·61) and
97·7 (SEM 0·11) % respectively.
Dogs performed well at a national level in races; the six-dog
team was placed fourth overall from twenty-nine competitors
(dog teams) and the four-dog team finished seventh out of
thirty-six competitors in the 2004 Australian Sled-dog Sports
Association (ASSA) National Point Scores. Veterinary
health checks conducted at weeks 0, 8 and 16 found all
dogs to be in good health and no abnormalities were detected.
Haematology results were consistent with published normal
ranges for haematological values for dogs
(14)
throughout the
study. Erythrocyte counts, PCV and Hb concentration
increased significantly (P,0·01) with time in both groups of
dogs (Table 4). There was no significant effect of diet, and
no significant interaction between diet and time, on any of
the blood characteristics measured in the present study.
Discussion
Dog foods are tested for their nutritional adequacy in the first
instance by means of chemical analysis. However, not all of
the nutrients present in the dog food will necessarily be avail-
able to the dog. This is why recognised feeding protocols are
Table 2. Analysed chemical composition of diets (as fed) and average daily intakes in twelve Siberian huskies
(Mean values and standard deviations for six animals per group)
Daily intake (per kg body weight
0·7 5
)
Content in diet (per kg) Meat-based diet Meat-free diet
Meat-based Meat-free Mean SD Mean SD
DM (g) 927 936 30·36 4·28 27·59 3·15
Gross energy (MJ) 20·9 21·1 0·68 0·10 0·73 0·08
Crude protein (g) 306 289 10·02 1·41 10·02 1·15
Crude fat (g) 166 165 5·44 0·77 5·72 0·64
Starch (g) 310 296 10·15 1·43 10·26 1·17
Free sugars (g) 7·5 19·8 0·25 0·03 0·69 0·08
Soluble NSP (g) 4·6 3·6 0·15 0·02 0·13 0·01
Insoluble NSP (g) 29·7 38·8 0·97 0·14 1·35 0·15
Total NSP (g) 34·3 42·4 1·12 0·16 1·48 0·17
W. Y. Brown et al.1320
British Journal of Nutrition
used to support nutritional adequacy claims. Where diets are
specifically formulated and marketed for active dogs, it
would seem that testing these diets in actively exercising
dogs would be a more appropriate test of the diet’s nutritional
adequacy for its designated purpose.
The present study is the first to demonstrate using a short
feeding trial that a meat-free diet can be nutritionally adequate
for exercising dogs. Whilst longer-term trials are necessary to
prove this claim, nutritional adequacy was shown by chemical
analyses, and this was further demonstrated by feeding the
diet, in a controlled experiment, to actively exercising dogs.
Each dog fed the meat-free diet was harnessed to a dog fed
the meat-based diet and therefore did exactly the same inten-
sity and amount of exercise. Blood profiles and veterinary
examinations indicated that all the dogs remained in good
health throughout the study irrespective of whether they
were fed diets based on animal or plant proteins. There is
only one other study reported in the literature that examines
a meat-free diet in exercising dogs and, in that study, dogs
fed the vegetable-protein diet developed anaemia (evidenced
by a significant decrease in Hb and erythrocyte counts)
whilst dogs fed the animal-protein diet showed no significant
haematological changes
(15)
.
Many human vegetarians have achieved prowess as athletes
and the nutritional considerations for vegetarian athletes have
been well documented
(16)
. Studies reported in the scientific
literature have found no differences in fitness or performance
between vegetarian and non-vegetarian athletes
(17,18)
and have
concluded that a balanced meat-free diet is not detrimental to
athletic performance
(19,20)
. All of the amino acids that are
known to be essential for man and for dogs can be obtained
from plant sources. However, there appears to be a propensity
for human vegetarians to have lower mean muscle creatine
(Cr) concentrations than omnivores
(21)
and as Cr is an import-
ant component of the energy delivery process, it has been
suggested that this could affect exercise performance. Supple-
menting diets with Cr has been shown to increase exercise
potential in humans, and it has been suggested that an
adequate supply of dietary Cr might also be important
for exercising dogs. Whilst moderate intakes of Cr could
be expected from consuming raw meat, commercial dog
foods provide very little Cr due to its degradation by heat
Table 3. Nutrient content of experimental diets and National Research
Council (NRC) recommended
(13)
allowances for maintenance in adult dogs*
Diet
Nutrient Meat-based Meat-free NRC recommended
Crude protein (g) 75·8 71·2 25·0
Essential amino acids
Arginine (g) 4·53 3·65 0·88
Histidine (g) 1·61 1·93 0·48
Isoleucine (g) 3·07 3·16 0·95
Leucine (g) 7·08 8·84 1·70
Lysine (g) 2·55 2·76 0·88
Methionine (g) 1·07 1·42 0·83
Phenylalanine (g) 3·62 4·09 1·13
Threonine (g) 3·02 2·78 1·08
Tryptophan (g) 0·50 0·55 0·35
Valine (g) 4·19 3·88 1·23
Crude fat (g) 41·1 40·7 13·8
Minerals
Ca (g) 3·5 2·3 1·0
P (g) 2·5 1·7 1·0
Mg (g) 0·3 0·3 0·2
Na (g) 2·2 2·1 0·2
K (g) 1·6 2·9 1·0
Fe (mg) 53·0 30·6 7·5
Cu (mg) 4·9 6·0 1·5
Zn (mg) 123·2 35·2 15·0
Mn (mg) 3·6 5·9 1·2
* All values reported are per 4184 kJ (1000 kcal) metabolisable energy.
Table 4. Changes in blood variables measured in Siberian huskies during a racing season in which dogs were fed either
meat-free or meat-based diets as their sole nutrient intake for 16 weeks
(Mean values with their standard errors for six animals per group)
Meat-based diet Meat-free diet P
Variable Mean SEM Mean SEM Diet Time Diet £time
Erythrocyte count ( £10
12
/l)* 0·54 0·002 0·46
Week 0† 6·52
a
0·27 6·02
a,b
0·12
Week 3 20·08
a
0·21 20·08
a
0·18
Week 8 0·47
b
0·34 0·28
a,b
0·25
Week 16 0·73
b
0·25 0·35
b
0·21
Hb (g/l)‡ 0·66 0·006 0·81
Week 0† 150·4
a
5·2 143·8
a,b
3·1
Week 3 20·8
a
4·1 21·9
a
3·9
Week 8 10·3
b
6·8 5·4
a,b
5·1
Week 16 9·4
b
5·4 7·1
b
3·4
Packed cell volume (%)§ 0·73 0·01 0·71
Week 0† 43·96
a
1·55 41·85
a
0·80
Week 3 20·35
a
1·39 20·10
a
1·14
Week 8 2·97
b
2·17 1·81
b
1·50
Week 16 3·22
b
1·61 2·14
b
1·15
a,b
Mean values for a variable within a column with unlike superscript letters were significantly different (P,0·05).
* The normal range for erythrocyte count in dogs is 5·5 to 8·5 £10
12
/l.
† Values measured at week 0 are baseline values. Data presented for weeks 3 to 16 are differences from baseline values.
‡ The normal range for Hb in dogs is 120 to 180 g/l.
§ The normal range for packed cell volume in dogs is 37 to 55 %.
Meat-free diet sustains exercising dogs 1321
British Journal of Nutrition
processing
(22)
. However, it is not essential for mammals to
have Cr in the diet, as it is synthesised in the body from the
amino acids arginine and glycine. Based on findings that
oral Cr supplementation did not lead to corresponding
increases in muscle concentrations in caged beagles
(23)
or in
racing greyhounds, and that Cr supplementation in racing
greyhounds did not improve performance
(24)
, it is unlikely
that a lack of dietary Cr would have any detrimental effect
on exercising dogs, provided that dietary intakes of arginine
and glycine are adequate.
Extraordinarily high daily ME intakes (4100 kJ/kg BW
0· 7 5
per d) have been recorded in Alaskan sled dogs racing long
distances (490 km) in freezing conditions
(25)
, whereas the
sled dogs in the present study raced over short distances in
mild climatic conditions. The average daily ME intakes of
the sled dogs in our experiment were calculated to be 572
(SEM 71) kJ/kg BW
0·7 5
per d and this is consistent with ME
requirements reported for moderately active border collies
(26)
.
The haematology results from the present study reveal some
interesting findings, but it should be emphasised that all values
were always within normal range. It should also be noted that
the observed increases in erythrocyte counts, PCV and Hb
were greatest in dogs fed the meat-based diet and that the
sample size (n6) might have been insufficient to detect signifi-
cant differences between the two dietary groups. In our experi-
ment, erythrocyte counts and PCV increased significantly
over time (P,0·01) in all dogs, whether they were fed the
meat-based or the meat-free diet. In contrast to this, both
PCV and erythrocytes decreased significantly (P,0·05) over
time in twelve sprint-racing Alaskan huskies during a
24-week training and racing season
(27)
. The Alaskan huskies
were fed diets that contained 20 and 24 % CP (as fed),
which is considerably less than the CP content of the diets
used in the present study (approximately 30 % CP). Another
experiment with thirty-two Alaskan sled dogs
(28)
found that
PCV and erythrocytes increased after training in dogs fed
diets of higher protein content (3·6, 5·3 and 6·1 g/kg BW per d)
but decreased in identically exercised dogs fed the diet with
the lowest CP content (3·0 g/kg BW per d). Dogs in the present
study received 4·7 g CP/kg BW per d, and the increase in
PCV and erythrocytes observed in our dogs is consistent
with these results. Human studies have shown that exercise
increases erythrocyte destruction
(29)
, but provided that this
does not exceed erythrocyte production then no detrimental
effects occur
(30)
. From the present study, and the work of
Reynolds et al.
(28)
, it appears that feeding dogs a higher
concentration of protein enabled a higher rate of erythrocyte
production, in excess of the numbers destroyed by exercise.
These findings highlight the importance of providing sufficient
dietary protein for exercising dogs, irrespective of whether
the protein is of plant or animal origin.
Conclusions
The present study is the first to demonstrate the potential for a
meat-free diet to be nutritionally adequate for exercising dogs.
In a 16-week controlled experiment, a meat-free diet main-
tained haematological characteristics in sprint-racing sled
dogs (Siberian huskies). Importantly, these findings pave the
way for commercial pet food manufacturers to produce nutri-
tionally adequate meat-free diets for dogs.
Acknowledgements
The present study was funded by an Australian Research
Council Linkage Grant to which Mars Petcare Australia
contributed as the industry partner. The authors would like
to thank Anne and Donal McIntyre (Malusky Kennels,
Belford, NSW, Australia) for allowing their dogs to participate
in the present study, and for their assistance throughout
the trial; and Dr Dorothy Robinson of NSW Department of
Primary Industries (Beef Industry Centre) for her assistance
with the statistical analysis.
An abstract of this research was presented at the 18th
Symposium of ‘Recent Advances in Animal Nutrition in
Australia’ (June 2005), University of New England, Armidale,
NSW, Australia.
Author contributions were as follows: W. Y. B., canine nutri-
tion, study design and oversight; B. A. V., veterinary haematol-
ogy; A. J. R., diet formulations; J. R. P., nutrition and physiology.
A. J. R. was employed by Mars Petcare Australia. None of
the other authors has any conflicts of interest to declare.
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