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Effect of dietary fat source and exercise on odorant-detecting ability of canine athletes

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Eighteen male English Pointers (2-4 years of age, 23.94+/-0.54 kg body weight) were allotted to three diet and two physical conditioning groups to evaluate the effect of level and source of dietary fat on the olfactory acuity of canine athletes subjected to treadmill exercise. Diet groups (6 dogs/diet) consisted of commercially prepared diets (minimum of 26% crude protein) containing 12% fat as beef tallow (A), 16% fat provided by equivalent amounts of beef tallow and corn oil (B), or 16% fat provided by equivalent amounts of beef tallow and coconut oil (C). This dietary formulation resulted in approximately 60% of the total fatty acid being saturated for diets A and C, while approximately 72% of the total fatty acids were unsaturated in diet B. One-half of the dogs within each dietary group were subjected to treadmill exercise 3 times per week for 30 min (8.05 km/h, 0% grade) for 12 weeks. All dogs were subjected to a submaximal exercise stress test (8.05 km/h, 10% slope for 60 min) every four weeks beginning at week 0. Olfactory acuity was measured utilizing behavioral olfactometry before and after each physical stress test. Non-conditioned (NON) dogs displayed a greater decrease (P<0.05) in olfactory acuity following exercise, while physically conditioned (EXE) dogs did not show a change from pre-test values. A diet by treatment interaction (P<0.10) was detected over the course of the study. NON dogs fed coconut oil had decreased odorant-detecting capabilities when week 4 values were compared with week 12 values. Feeding a diet that is predominately high in saturated fat may affect the odorant-detecting capabilities of working dogs. Additionally, these data indicate that utilization of a moderate physical conditioning program can assist canine athletes in maintaining olfactory acuity during periods of intense exercise.
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Effect of dietary fat source and exercise on odorant-detecting
ability of canine athletes
Eric K. Altom
a,1
, Gary M. Davenport
a,1
, Lawrence J. Myers
b
, Keith A. Cummins
a,*
a
Department of Animal and Dairy Sciences, College of Agriculture, Auburn University, AL 36849-5415, USA
b
Department of Anatomy, Physiology, and Pharmacology, College of Veterinary Medicine, Auburn University, AL 36849, USA
Accepted 13 February 2003
Abstract
Eighteen male English Pointers (2–4 years of age, 23:94 0:54 kg body weight) were allotted to three diet and two physical
conditioning groups to evaluate the effect of level and source of dietary fat on the olfactory acuity of canine athletes subjected to
treadmill exercise. Diet groups (6 dogs/diet) consisted of commercially prepared diets (minimum of 26% crude protein) containing
12% fat as beef tallow (A), 16% fat provided by equivalent amounts of beef tallow and corn oil (B), or 16% fat provided by
equivalent amounts of beef tallow and coconut oil (C). This dietary formulation resulted in approximately 60% of the total fatty acid
being saturated for diets A and C, while approximately 72% of the total fatty acids were unsaturated in diet B. One-half of the dogs
within each dietary group were subjected to treadmill exercise 3 times per week for 30 min (8.05 km/h, 0% grade) for 12 weeks. All
dogs were subjected to a submaximal exercise stress test (8.05 km/h, 10% slope for 60 min) every four weeks beginning at week 0.
Olfactory acuity was measured utilizing behavioral olfactometry before and after each physical stress test. Non-conditioned (NON)
dogs displayed a greater decrease (P<0:05) in olfactory acuity following exercise, while physically conditioned (EXE) dogs did not
show a change from pre-test values. A diet by treatment interaction (P<0:10) was detected over the course of the study. NON dogs
fed coconut oil had decreased odorant-detecting capabilities when week 4 values were compared with week 12 values. Feeding a diet
that is predominately high in saturated fat may affect the odorant-detecting capabilities of working dogs. Additionally, these data
indicate that utilization of a moderate physical conditioning program can assist canine athletes in maintaining olfactory acuity
during periods of intense exercise.
Ó2003 Elsevier Science Ltd. All rights reserved.
Keywords: Dietary fat; Canine; Athlete; Odorant; Exercise; Olfaction; Fatty acid; Behavioral olfactometry
1. Introduction
Acceptable performance of many working canines is
highly dependent on the olfactory acuity of the animal.
Currently, working canines provide a variety of services
to our society including the detection of narcotics, ex-
plosives, and other contraband. Additionally, these ca-
nine athletes are utilized in outdoor sporting events such
as hunting and field trial competitions (Holloway, 1961).
Olfactory acuity is measured as the lowest concentration
of a selected odorant that can be detected by an or-
ganism. The olfactory acuity of dogs is exceptional
based on their ability to detect compounds that range in
concentrations from 1016 to 1018 M/L (Moulton and
Marshall, 1981; Myers, 1991a). Although limited re-
search is available, conditions such as canine distemper
(Myers et al., 1988a) and canine parainfluenza virus
infections (Myers et al., 1988b) may alter canine olfac-
tory acuity. Other clinical trials suggest that olfactory
sensitivity may be affected by hypothyroidism, seizure
disorders, diabetes mellitus and head trauma (Myers,
1991b).
Trainers have traditionally utilized high carbohydrate
diets in an effort to maintain acceptable performance of
canine athletes. This practice is based on reports of en-
hanced levels of performance when humans athletes
consume high carbohydrate diets (Brotherhood, 1984;
Research in Veterinary Science 75 (2003) 149–155
www.elsevier.com/locate/rvsc
*
Corresponding author. Fax: +1-334-844-1519.
E-mail address: kcummins@acesag.auburn.edu (K.A. Cummins).
1
Present address: Research and Development, The Iams Company,
P.O. Box 189, Lewisburg, OH 45338, USA.
0034-5288/$ - see front matter Ó2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0034-5288(03)00071-7
Coyle, 1992). In contrast, research using canine athletes
has shown several beneficial effects of feeding increased
dietary fat on physical performance. Dietary fat during
exercise spares blood glucose and muscle glycogen re-
serves (Kronfeld et al., 1994). Reynolds et al. (1995)
reported that trained sled dogs fed high fat diets relied
less on glucose oxidation to maintain intense physical
activity compared with sled dogs fed a high carbohy-
drate diet, and were able to sustain the intensity level of
physical activity for a longer period of time. While in-
creased dietary fat is a proven performance enhancing
tool in canine athletes, it is not known whether the di-
etary fat level and (or) dietary fatty acid composition
affects olfactory acuity and odorant-detecting capabili-
ties of dogs.
Clandinin et al. (1985) reported that fatty acid con-
tent of the intestinal mucosa and adipose tissue was al-
tered by dietary fat consumption. Foot et al. (1983)
indicated that nutritionally adequate diets containing
various dietary fat sources altered the fatty acid content
and composition of lipids in the brain. Changes in
neurocellular membranes can alter the activity of lipid-
dependent enzymes required for neurotransmission
(Gerbi et al., 1994, 1993). Therefore, it is plausible that
altering the ratio of dietary saturated and unsaturated
fatty acids will alter the fatty acid composition of the
nasal epithelium of canine athletes resulting in altered
olfactory function. This hypothesis is based on research
that indicates different sources of dietary fat alter the
fatty acid composition and functionality of various cel-
lular membranes (Campbell and Dorn, 1992; Periago
et al., 1990; Sebokva et al., 1990). No experiments have
been published that have evaluated the effects of dietary
components on the odorant-detecting capabilities of
canine athletes. Therefore, the objective of this study
was to investigate the effects of dietary fat (source and
level) and physical conditioning on the olfactory acuity
of canine athletes subjected to treadmill exercise.
2. Materials and methods
2.1. Animals
Eighteen healthy, performance bred, male pointers
(2–4 years of age, 23:94 0:54 kg body weight) were
selected from kennels from across the Southeast region
of the United States. All dogs received complete physical
examinations by the project clinician and were pro-
nounced to be in normal health prior to entering the
study. No dog had received regular physical condition-
ing or field training for at least 6 months prior to initi-
ation of the study. Dogs were housed individually in
USDA approved kennel facilities located at the Auburn
University College of Veterinary Medicine campus for
the duration of the study. All procedures were pre-ap-
proved by the Institute Animal Care and Use Commit-
tee for Auburn University and were in accordance with
the Guide for the Care and Use of Laboratory Animals
(National Research Council, 1996). All dogs successfully
completed this study.
2.2. Diets and feeding regimes
The term ‘‘diet’’ refers to the formulation of the
feed presented to each dog during the study. All dogs
were given free access to fresh water and fed a com-
plete and balanced dry diet (Diet A, control) con-
taining a minimum of 26% crude protein and 12%
crude fat (comprised of beef tallow), during a four
week acclimation period prior to the initiation of the
study. This control diet formulation was selected for
this study because a similar diet was being commer-
cially marketed as an appropriate diet for adult ath-
letic dogs.
For the experiment, dogs were allotted to one of the
three diet groups (6 dogs/diet group). The diets were
formulated based on Association of American Feed
Control Officials nutrient requirements for adult dogs
Table 1
Diet formulasa
Ingredientb(as-fed) Diet Ac
(control)
Diet Bd
(unsaturated)
Diet Ce
(saturated)
Ground yellow corn 36.0 29.1 29.1
Soybean meal 15.4 17.8 17.8
Corn gluten meal 13.5 16.0 16.0
Rice bran 11.0 11.0 11.0
Beef tallow 8.0 4.0 4.0
Corn oil 8.0
Coconut oil —— 8.0
Beef and bone meal 6.5 2.0 2.0
Wheat 6.0 6.0 6.0
Brewers yeast 1.0 1.0 1.0
Dog vitamin pre-mix 0.7 0.7 0.7
Salt 0.6 0.7 0.7
Dicalcium phosphate 0.5 1.6 1.6
Calcium carbonate 0.3 1.1 1.1
Trace mineral pre-mix 0.2 0.2 0.2
Lysine 0.2 0.2 0.2
Potassium 0.1 0.1 0.1
Choline 0.05 0.05 0.05
a
Manufactured by Ralston–Purina, St. Louis, MO.
b
Values reported as percentage of total diet mixture.
c
Diet A (control): 12% crude fat (4% beef tallow added internally in
diet mixture, 4% beef tallow added externally as a sprayed product
following extrusion, and remaining 4% dietary fat derived from basal
ingredients).
d
Diet B (unsaturated): 16% crude fat (4% beef tallow added inter-
nally in diet mixture, 4% beef tallow and 4% corn oil added externally
as a sprayed product following extrusion, and remaining 4% dietary fat
derived from basal ingredients).
e
Diet C (saturated): 16% crude fat (4% beef tallow added internally
in diet mixture, 4% beef tallow and 4% coconut oil added externally as
a sprayed product following extrusion, and remaining 4% dietary fat
derived from basal ingredients).
150 E.K. Altom et al. / Research in Veterinary Science 75 (2003) 149–155
(1996) and fed as an extruded dry product manufactured
by Ralston–Purina Company, St. Louis, MO (Tables 1
and 2). Diet B contained a minimum of 26% crude
protein and 16% crude fat provided by equal amounts
of beef tallow and corn oil. Diet C contained a minimum
of 26% crude protein and 16% crude fat provided by
equal amounts of beef tallow and coconut oil. Diet
formulations resulted in diet B containing predomi-
nately unsaturated fatty acids, while diet C contained
predominately saturated fatty acids (Table 3). Nutrient
composition of each diet was analyzed utilizing the
methods approved by the Association of Official Ana-
lytical Chemists (16th edition, 1995).
2.3. Physical conditioning program
Dogs from each diet group were allotted to two
conditioning groups (physically conditioned and non-
conditioned). Physically conditioned dogs (EXE) were
exercised three times weekly on a motorized treadmill
(Parker Treadmills, Auburn, AL) at a rate of 8.05 km/h
(0% slope) for 30 min/day on non-consecutive days.
Non-conditioned dogs (NON) were exercised at
8.05 km/h (0% slope) for 10 min/day one day per week to
ensure familiarity with the treadmill. Duration of the
physical conditioning program was 12 weeks. The
physical conditioning program was developed to closely
simulate traditional techniques utilized by performance
field dog trainers to condition their competitors (Tar-
rant, 1977; Wehle, 1964).
2.4. Physical stress testing
All dogs were subjected to a submaximal exercise
stress test on weeks 0, 4, 8 and 12 of the study. During
the two-stage exercise test, dogs were initially exercised
at a rate of 8.05 km/h (5% slope) for 15 min, and then at
a rate of 8.05 km/h (10% slope) for 45 min. The physical
test was concluded at 60 min or when the dog refused to
continue.
2.5. Odorants and subject preparation
Olfactory acuity is measured as the lowest concen-
tration of a selected odorant which is detectable by an
Table 2
Composition analysis of test dietsa
Dietary component
(as-fed)
Diet A
(control)
Diet B
(unsaturated)
Diet C
(saturated)
Digestible energy
(kcal/kg)b
4085 4322 4321
Moisture (%) 7.3 5.3 5.0
Protein (%) 26.5 26.6 26.0
NFE (%) 46.1 42.5 42.5
Fat (%) 12.6 16.9 16.8
Fiber (%) 1.3 1.3 1.3
Ash (%) 5.8 6.4 6.4
Calcium (%) 1.0 1.0 1.0
Phosphorus (%) 0.8 0.8 0.8
Sodium (%) 0.3 0.3 0.3
Potassium (%) 0.6 0.6 0.6
Chloride (%) 0.5 0.5 0.5
a
Manufactured by Ralston–Purina, St. Louis, MO.
b
Calculated value.
Table 3
Fatty acid composition of test dietsa
Fatty acidbDiet Ac(control) Diet Bd(unsaturated) Diet Ce(saturated)
Caprylic 8:0 —— 2.9
Capric 10:0 —— 2.5
Lauric 12:0 0.3 21.5
Myristic 14:0 1.9 1.0 9.7
Palmitic 16:0 20.8 15.4 14.9
Palmitoleic 16:1 2.1 1.0 1.0
Margaric 17:0 1.0 0.5 0.5
Stearic 18:0 14.2 7.3 7.9
Oleic 18:1 36.5 29.6 21.2
Linoleic 18:2, n6 17.2 40.0 13.9
-Linolenic 18:3, n3 0.9 1.1 0.7
Total saturated fatty acids 37.9 24.5 59.9
Total unsaturated fatty acids 56.8 71.7 36.8
Remaining fatty acids 5.3 3.8 3.3
Omega 6:3 19.1:1 36.4:1 19.9:1
a
Manufactured by Ralston–Purina, St. Louis, MO.
b
Values reported as percent of total fat contained in the diet.
c
Diet A (control): 12% crude fat (4% beef tallow added internally in diet mixture, 4% beef tallow added externally as a sprayed product following
extrusion, and remaining 4% dietary fat derived from basal ingredients).
d
Diet B (unsaturated): 16% crude fat (4% beef tallow added internally in diet mixture, 4% beef tallow and 4% corn oil added externally as a sprayed
product following extrusion, and remaining 4% dietary fat derived from basal ingredients).
e
Diet C (saturated): 16% crude fat (4% beef tallow added internally in diet mixture, 4% beef tallow and 4% coconut oil added externally as a
sprayed product following extrusion, and remaining 4% dietary fat derived from basal ingredients).
E.K. Altom et al. / Research in Veterinary Science 75 (2003) 149–155 151
organism. Olfactory thresholds were determined for all
dogs prior to the initiation of this study by behavioral
olfactometry utilizing eugenol (Sigma Chemical Com-
pany, St. Louis, MO) as the odorant (Ezeh et al., 1992;
Myers and Pugh, 1985). Dilutions of ascending con-
centration of eugenol from 1018 to 101M/L of stock
solutions of eugenol (6.52 M) in propylene glycol (Fisher
Scientific Company, Fair Lawn, NJ) were utilized to
determine odorant-detecting thresholds 30 min prior to
the treadmill physical stress test and 30 min following
the conclusion of the physical stress test. Eugenol was
selected as the test odorant based on its ability to
stimulate olfactory nerve activity with little or no effect
on trigeminal activation (Doty, 1989). One milliliter of
each dilution was stored in a separate sealed 12 75 mm
borosilicate test tube (Fisher Scientific Company, Fair
Lawn, NJ). Odorless blanks were used that contained
1 mL of pure propylene glycol. Care was taken to pre-
vent any cross-contamination of the sample vials.
Subjects were prepared according to previously de-
scribed techniques for behavioral olfactometry (Ezeh
et al., 1992; Myers and Pugh, 1985). Dogs were blind-
folded and lightly restrained in a right lateral recum-
bency and allowed to acclimate for a minimum of 5 min
to the environment before the evaluation was initiated.
Efforts to create a stimulus-neutral environment (Myers,
1991a) within the testing room included adequate ven-
tilation, temperature control (25 1°C), white noise to
prevent excessive auditory stimulus, and odor control
(no perfume, cologne, or smoking allowed, and baking
soda bags were utilized as odor absorbents). All dogs
were calm prior to odor presentation, as indicated by
minimal spontaneous body movement.
2.6. Olfactory function evaluation
Baseline odorant-detecting thresholds for eugenol
were established for each dog using triplicate measure-
ments on non-consecutive days using previously de-
scribed techniques (Ezeh et al., 1992; Myers and Pugh,
1985). The same evaluators performed all olfactory
threshold measurements throughout the study. The av-
erage of these values was determined to be the baseline
odorant-detecting threshold value for each dog. The
olfactory acuity for all dogs was determined to be within
normal ranges (Myers, 1991b) prior to inclusion in the
study. Normal range was determined to be the detection
of an odor concentration less than 109M/L eugenol
(Myers, 1991b).
Each olfactory evaluation test was initiated by pre-
senting the blind-folded dog with the empty test tube
holder, a sample blank (pure propylene glycol), and then
the individual test tray containing the serial dilution set
with three additional blanks randomly placed in the set.
The method of presenting the samples was similar to
that previously described (Ezeh et al., 1992; Myers and
Pugh, 1985). Each individual sample tube was opened
and placed approximately 2 cm ventral to the tip of the
dogÕs nose. Each dilution was presented for 10 s, with-
drawn for 15 s, and then followed by the next sample in
the serial dilution set. Thresholds for odorant-detection
were determined to be the lowest eugenol concentration
that evoked an observable, reflexive behavioral re-
sponse. Behavioral responses were videotaped and an-
alyzed by four observers trained to detect the
appropriate behavioral response. A positive olfactory
response was determined by the presence of a pre-de-
termined typical behavior pattern of a sniff. Observers
independently agreed in every case of response or lack of
response to odor stimuli at a given concentration. The
18 tenfold dilutions were recorded as the negative log of
the dilution with 1 being the most concentrated and 18
being the least concentrated. A score of 0 was recorded
for lack of response. This study was conducted as a
double-blind experiment.
2.7. Statistical analysis
Dogs were allotted randomly to diet and conditioning
groups. Data were analyzed as a double split plot over
time design, with diet, conditioning, week, and time as
main effects. The experimental unit was dog within diet
and conditioning group. Initial olfactory estimates col-
lected at week 0 were utilized as covariates to assess
changes in olfactory acuity during the experimental pe-
riod. The general linear model (GLM) procedure of SAS
(Statistical Analysis Systems Version 6.12, SAS Institute,
Cary, NC) was utilized for statistical analyses. Differences
among treatment least squares means were separated
utilizing the PDIFF option of SAS when protected by a
significant (P<0:10) F-test. Initially a complete model,
including all three-way interactions, was used to analyze
these data. However, three-way interactions that were not
significant (P>0:10), as determined by ANCOVA, were
eliminated from the final analysis.
3. Results
No differences were detected in baseline olfactory
acuity prior to the initiation of the study, and mean
acuity (expressed as the negative log of the minimum
eugenol concentration needed to elict a behavioral re-
sponse) was 16:31:2 (SEM). In contrast, physical
conditioning affected olfactory acuity (P<0:05) fol-
lowing the one hour of physical stress test with dogs
receiving physical conditioning three days per week
(EXE) having greater odorant-detecting capabilities
compared with NON dogs (Table 4). NON dogs had a
64% reduction in olfactory acuity following the physical
stress test based on pre and post-exercise values. How-
ever, pre and post-exercise values for EXE dogs were
152 E.K. Altom et al. / Research in Veterinary Science 75 (2003) 149–155
similar (P>0:10). NON dogs fed coconut oil had de-
creased (P<0:10) olfactory acuity when pre-test
threshold values obtained at week 4 were compared with
values subsequently obtained at week 12 (Table 5).
Likewise, EXE fed the control diet had significantly
(P<0:10) lower olfactory acuity when values obtained
at week 4 were compared with values obtained at week
12. All remaining diet–physical conditioning combina-
tions were similar (P>0:10) across the study period. No
evidence of olfactory function was present in NON dogs
fed coconut oil at week 12 values (Table 5). It is im-
portant to note that these values were obtained prior to
any physical exertion. The calculated percent change
between pre-test olfactory values and post-test olfactory
values indicated that EXE dogs and NON dogs fed diets
B and C were not different (P>0:10).
4. Discussion
The sport of field trials is one of the fastest growing
outdoor activities in the United States. However, since the
beginning of field competitions, trainers have searched for
methods to improve canine performance. Holloway
(1961) reported that 85% of hunting dog owners surveyed
indicated some type of olfactory problem. Although the
source of these conditions was not determined, olfactory
function remains a primary concern for trainers of canine
athletes. Myers and coworkers (1988a, 1988b, 1991b)
have documented several conditions which affect the ol-
factory function of canines. These conditions include ca-
nine distemper and parainfluenza viral infections.
However, these conditions are not believed to be the cause
of impaired olfactory function in this study due to the fact
that precautionary physical examinations, an aggressive
vaccination program, and baseline olfactory measure-
ments were performed prior to the initiation of the pro-
ject. Additionally, all dogs were examined throughout the
study and none displayed clinical signs of any upper re-
spiratory or viral infection.
While some anecdotal evidence exists in the popular
press, these data are the first to indicate scientifically a
beneficial effect of physical conditioning on the olfactory
acuity of canine athletes when subjected to moderate
exercise. Behavioral olfactometry measurements re-
vealed canine athletes enrolled in a physical condition-
ing program were able to maintain a greater olfactory
acuity compared with dogs that were not physically
conditioned. Non-conditioned dogs displayed a 63.6%
decrease in olfactory acuity following treadmill exercise,
while EXE dogs showed no significant changes (Table
4). These data may possibly be explained by altered re-
spiratory function of the dogs during exercise. Dogs that
are not in adequate physical condition breathe more
through the mouth during periods of intense exercise as
opposed to breathing through the nose when exposed to
intense physical exertion. Because of increased heat load
during exercise, dogs force more air through the lungs
and out of the mouth to regulate body temperature. It is
highly probable that decreasing the amount of airflow
through the nasal passage reduces the amount of
odorants passing over the olfactory membranes. This
Table 4
Olfactory acuity of canine athletes pre and post-treadmill exercise1
Conditioning2NON EXE
No. of dogs 9 9
Pre-stress test 10:71:3ac 7:81:4ac
Post stress test 3:91:4ad 8:11:2bc
Percent change (%)3)63.6 3.8
1
LSMeans SEM. Values represent the negative log of the mini-
mum eugenol concentration that elicited a behavioral response.
2
Conditioning: NON, non-conditioned; EXE, physically condi-
tioned.
3
Percent change in olfactory acuity between pre-stress test values
and post stress test values.
abIndicate differences within time period. Means within the same time
period lacking a common superscript differ (P<0:05).
cdIndicate differences within conditioning group. Means within the
same conditioning group lacking a common superscript differ
(P<0:05).
Table 5
Effects of dietary fat source and physical conditioning on the olfactory thresholds of canine athletes throughout the project test period1
Conditioning3Diet2SEM
Diet A Diet B Diet C
NON EXE NON EXE NON EXE
No. of dogs 3 33333
Week 4 18.0a12.0a11.0a11.3a18.0a12.0a2.9
Week 8 13.7a7.7a;b10.3a5.3a11.3a6.3a2.9
Week 12 15.0a4.7b4.7a6.0a0.0b11.0a2.9
1
LSMeans SEM. Values represent the pre-stress test, values reported as the negative log of the minimum eugenol concentration, that elicited a
behavioral response.
2
Diets: Diet A, control containing 12% fat as beef tallow; Diet B (unsaturated), containing 16% fat (8% beef tallow and 8% corn oil); Diet C
(saturated), containing 16% fat (8% beef tallow and 8% coconut oil).
3
Conditioning: NON, non-conditioned; EXE, physically conditioned.
a;bIndicated differences within diet-conditioning group. Means within the same diet-conditioning group lacking a common superscript differ
(P<0:10).
E.K. Altom et al. / Research in Veterinary Science 75 (2003) 149–155 153
mechanism could substantially reduce the ability of the
athlete to detect odors both during and following peri-
ods of intense exercise. Likewise, increased dehydration
of the nasal mucosal layer of poorly conditioned dogs
would contribute to the altered function of the olfactory
system due to total body dehydration.. It is highly
probable that dehydration of the nasal mucosal mem-
brane would result in decreased enzyme activity and
decreased membrane fluidity. These conditions could
alter neuro-signal transduction and odorant receptor
function in the olfactory mucosal layer, thereby poten-
tially impairing olfactory function in canine athletes.
Conversely, a canine in top physical condition would be
able to reduce the amount of air breathed through the
mouth. Hydration status following exercise was not
quantitatively measured in this experiment. Although
the complete mechanism for decreased odor detection in
non-conditioned canine athletes was not fully defined in
this experiment, a combination of decreased airflow
across the nasal membranes and/or decreased hydration
status of the mucosal layer may significantly decrease
odor detection capabilities in these canine athletes.
Several studies report alterations in functionality of
organ and tissues in response to different dietary fat
sources. Therefore, these diet-induced responses may
also affect nasal epithelial composition and function
when dogs are fed various fat sources. MacDonald et al.
(1996) reported altered brain membrane phospholipid
concentrations in rats during long term feeding of sat-
urated versus unsaturated fatty acids. They reported
that a diet comprised of saturated fatty acids resulted in
a deficiency of 18:3 fatty acids in the brain. Membrane
phospholipids provide a hydrophobic barrier between
the environment and the cell (MacDonald et al., 1996).
The fatty acid composition of membrane phospholipids
dictates the fluidity and permeability of the membrane
(Couture and Hulbert, 1995). Therefore, alteration of
the membrane fatty acid composition may alter the
function of the membrane due to changes in fluidity
which, in turn, alters the function of membrane en-
zymes. While the complete olfaction mechanism is not
defined, major components that mediate the molecular
events of olfaction include one or more odorant-binding
proteins, odorant-sensitive adenylate cyclase, and sodi-
um-potassium ATPase. Sodium–potassium ATPase is
one enzyme in brain synaptic membranes that has been
reported to be altered by dietary fat (Gerbi et al., 1994).
Our data show a possible differential response to di-
etary fat source and exercise. Dietary fat source and(or)
level did not alter the olfactory acuity of the physically
conditioned (EXE) dogs. However, NON dogs fed co-
conut oil showed no evidence of odor detecting ability at
week 12 of the study (Table 5). Similarly, EXE dogs fed
the control diet had significantly reduced olfactory
function prior to exercise when values obtained at week
4 were compared to values obtained at week 12 of the
study. No differences were detected among the remain-
ing diet-conditioning groups.
5. Summary
Physical conditioning of canine athletes prevented a
reduction in olfactory acuity following one hour of
treadmill exercise. Although further studies are required,
these data indicate a beneficial effect of regular physical
conditioning for canine athletes that are engaged in ac-
tivities which require quality odorant-detecting capa-
bilities. Additionally, feeding increased levels of
saturated fatty acids to unconditioned dogs could result
in poor olfactory detecting performance. While further
investigations are warranted, data derived from this
study suggest that high levels of saturated fat can further
reduce the odorant-detecting capabilities of poorly
conditioned canines. These factors should be considered
when developing a training program for canine athletes.
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... Exercise and condition deficiencies are described as physical stressors which may affect the olfaction in canines directly or indirectly [58]. Physical exercise affects the olfaction of detection dogs by decreasing finding rates, especially in dogs with poor physical conditions [88,89]. As a result, a working dog should be well trained to have an optimal physical condition [90]. ...
... As a result, a working dog should be well trained to have an optimal physical condition [90]. Scent detection training techniques can improve odour sensitivity and discrimination [89][90][91][92]. Housing and general management may influence the dogs' detection work as well by affecting the learning capability. ...
... Hydration [84], nutrition [88,89], and the microbiome [58] of dogs manipulate the olfactory sense as well. As mentioned above, heat stress influences olfaction due to provocation of panting but dogs are able to develop heat tolerance by establishing an adequate hydration status [84,89]. ...
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The extraordinary olfactory sense of canines combined with the possibility to learn by operant conditioning enables dogs for their use in medical detection in a wide range of applications. Research on the ability of medical detection dogs for the identification of individuals with infectious or non-infectious diseases has been promising, but compared to the well-established and–accepted use of sniffer dogs by the police, army and customs for substances such as money, explosives or drugs, the deployment of medical detection dogs is still in its infancy. There are several factors to be considered for standardisation prior to deployment of canine scent detection dogs. Individual odours in disease consist of different volatile organic molecules that differ in magnitude, volatility and concentration. Olfaction can be influenced by various parameters like genetics, environmental conditions, age, hydration, nutrition, microbiome, conditioning, training, management factors, diseases and pharmaceuticals. This review discusses current knowledge on the function and importance of canines’ olfaction and evaluates its limitations and the potential role of the dog as a biomedical detector for infectious and non-infectious diseases.
... Immediately following extreme physical exercise, there is a reduction in the sniffing rate and increased panting rate which result in reduced olfaction performance (32). This may be explained by the fact that non-conditioned canines pant harder during intense exercise instead of breathing through their nose, which decreases the quantity of odorants passing over olfactory epithelium in the nasal cavity (77). It seems clear that physical conditioning (specifically as pertains to minimizing panting) may support improved olfaction in the detection dog. ...
... Dehydration of the nasal mucosal membrane results in decreased enzyme activity and decreased membrane fluidity, altering neurosignal transduction and odorant receptor function. A combination of decreased airflow and dehydration of the mucosal layer can significantly decrease odor detection capabilities in the working canine (77). Dehydration in search-and-rescue canines was reported to occur in dogs working after the terrorist attacks on 9/11 (91,92), the Haiti earthquake (93), and the Washington landslide (94). ...
... Exercise and diet seem to be inextricably linked to canine performance, but there are few studies examining the relationship between these elements of detection dog management. English Pointers withheld from exercise and fed a diet supplemented with coconut oil appeared to experience compromised olfaction, but exercised dogs maintained olfactory acuity (77). The authors reported greater olfactory sensitivity for all exercised dogs regardless of dietary fat source (beef tallow; beef tallow + corn oil; beef tallow + coconut oil). ...
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The impact of health, management, and microbiota on olfactory function in canines has not been examined in review. The most important characteristic of the detection canine is its sense of smell. Olfactory receptors are primarily located on the ethmoturbinates of the nasal cavity. The vomeronasal organ is an additional site of odor detection that detects chemical signals that stimulate behavioral and/or physiological changes. Recent advances in the genetics of olfaction suggest that genetic changes, along with the unique anatomy and airflow of the canine nose, are responsible for the macrosmia of the species. Inflammation, alterations in blood flow and hydration, and systemic diseases alter olfaction and may impact working efficiency of detection canines. The scientific literature contains abundant information on the potential impact of pharmaceuticals on olfaction in humans, but only steroids, antibiotics, and anesthetic agents have been studied in the canine. Physical stressors including exercise, lack of conditioning, and high ambient temperature impact olfaction directly or indirectly in the canine. Dietary fat content, amount of food per meal, and timing of meals have been demonstrated to impact olfaction in mice and dogs. Gastrointestinal (GI) microbiota likely impacts olfaction via bidirectional communication between the GI tract and brain, and the microbiota is impacted by exercise, diet, and stress. The objective of this literature review is to discuss the specific effects of health, management, and microbiota shifts on olfactory performance in working canines.
... Physical fitness and proper dietary management are mainstays for peak performance across athletes and athletic disciplines. It is not surprising that there is evidence to suggest that diet and fitness can impact olfactory function in dogs [ 81,101,102]. Physical fitness is critical for overall performance in working breeds. Broadly, lack of conditioning results in increased physiological response to exercise and strenuous activity such as increased respiration and panting, elevated heart rate and elevated temperature. ...
... Broadly, lack of conditioning results in increased physiological response to exercise and strenuous activity such as increased respiration and panting, elevated heart rate and elevated temperature. Cardiovascular conditioning improves the olfactory performance following exercise, likely through reduction of physiological responses such as panting which reduces exposure of odorant and nasal airflow to the olfactory recess [26,102]. Dietary management is necessary for maintaining peak physical fitness and body conditioning, and fluctuations too large in either direction can be detrimental to performance and place the dog at risk for injury or illness due to working demands [101]. ...
... Certain food compositions and ingredients can enhance or decrease olfactory acuity (120), which seems to be dependent on the level of physical exercise in dogs. Angle et al. found benefits to olfactory performance when corn oil supplemented diets were used together with exercise (125), whereas feeding coconut oil supplemented diets without exercise impaired olfaction (126). Interestingly, relatively few studies exist concerning commonly used drugs in dogs and their impact on olfactory performance (77). ...
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The respiratory coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) quickly developed into a pandemic (1). Even though laboratory diagnostic tests and vaccines were consequently developed (2, 3), the exploration of rapidly deployable, more reliable tools for addressing the current and future pandemics was vital. Toward this goal, researchers worldwide evaluated the use of medical detection dogs as a rapid, reliable and cost-effective screening method for SARS-CoV-2 infections (4). The ability of dogs to distinguish diseases by their high-resolution sense of smell is based on the volatile organic compound (VOC)-hypothesis (5). Numerous infectious and non-infectious diseases change metabolic processes releasing characteristic VOC-patterns in the form of an “olfactory fingerprint” (6–10). Many studies have shown that dogs can detect metabolic disorders, such as cancer (11) and hypoglycemia (12), predict epileptic seizures (13, 14), or even distinguish various pathogens (8, 15–17). Approximately 78% of the 27 SARS-CoV-2-canine detection studies reviewed by Meller et al. yielded > 80% sensitivity and approximately 60% of studies yielded > 95% of specificity (4), highlighting the potential of the dog as a “diagnostic system” and its recommendation for certain settings. Despite these promising results, all studies published up to now differed in numerous design features. They were mostly designed as pilot studies and case-control selection of patients was mostly favored over a more preferable cross-sectional (“cohort”) selection [study quality assessment was conducted and presented by Meller et al. (4)]. The aim of this comprehensive review summary is to provide a general overview of the divergent aspects that may impact canine disease detection and to provide recommendations for future deployment of medical detection dogs (see also summary in Table 1). Specific emphasis is placed on the choice of dogs, training paradigms, safety aspects, sample characteristics, pre-screen processing (e.g., inactivation), and screening-population and its environment related aspects, respectively (see also Figure 1 and Supplementary Figure 1), providing an outlook and proposals for the future standardization in the use of dogs for disease detection. Ultimately, this report provides a blueprint for the potential use of medical detection dogs in future epidemics and pandemics.
... Dietary and nutritional supplements have shown varying degrees of influence on olfaction. In a study by Angle and colleagues, 18 supplementation with corn oil showed an improvement on olfaction, whereas a study by Altom and colleagues 19 showed supplementation with coconut oil representing 8% of a 16% fat diet was associated with olfactory impairment. Further studies are needed to make recommendations on dietary supplements and olfactory function. ...
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Canine companions have learned to aid in performing tasks and conducting work for decades. Areas where unique capabilities of working dogs are harnessed are growing. This expansion, alongside efforts to increase domestic purpose-bred stock and awareness of the important role working dogs play in society, is increasing the role veterinarians provide. This article provides a brief overview of 3 key sensory systems in working dogs and highlights considerations for care related to each olfaction, audition, and vision.
... In addition, we found a positive influence of physical exercise on odor threshold. Altom et al. (11) had similar finding in dogs, revealing that suitable physical activity improves odor sensitivity in dogs. However, when we explored the impact of physical exercise type, we found that not all the types of physical exercise examined in this research had a positive effect on olfactory functions. ...
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Background: Although ageing and neurodegenerative diseases, including Alzheimer disease, have been associated with olfaction impairment, studies exploring how to ameliorate this impairment are limited. The aim of the present study was to determine the effect of various types of physical exercise on olfaction decline in ageing. Methodology: 99 healthy community-dwelling participants (85 women; mean (SD) age, 62.5 (5.7) years) were included. All the participants were required to complete the tests consisting of a questionnaire, cognitive test and olfaction test. Results: Odor identification scores for participants who exercised regularly for more than 1 year (more than 3 times/wk; more than 30 min each time) were significantly higher than those for non-exercisers, and odor detection threshold scores were significantly higher in the exercisers. Both odor threshold and odor identification scores for those who exercised by practicing taiji (tai chi), dancing, or running were significantly better than those for participants who exercised by walking or who did not exercise. Conclusion: Compared with those among older people who did not exercise, measures of olfaction among older adults who exercised were better, and the type of physical exercise mattered. Therefore, if physical exercise intervention is suggested to prevent or delay olfactory deterioration in older adults, the type of physical exercise should be considered.
... Feeding higher fat diets may improve stamina and olfactory ability, but the source of the fat is also important. Saturated fats (i.e., coconut oil) are reported to decrease olfactory acuity, while polyunsaturated fats (i.e., corn oil) improved olfactory efficiency (5,6). Dietary fat may also impact thermodynamics. ...
... The acquisition of forensic evidence by law enforcement officers, including canines, is subject to scrutiny, and factors that reduce the reliability of the detection dog may be introduced in court [12,13]. Multiple factors may affect the olfactory performance of a dog, including breed [9], diet, and exercise [14], disease and certain medications [15] although many gaps in the research remain [16]. The only medications confirmed to diminish canine olfaction are the antibiotic, metronidazole [17] and the steroids (high doses of dexamethasone or hydrocortisone combined with deoxycorticosterone) [18]. ...
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Fentanyl is a potent opioid used clinically as a pain medication and anesthetic but has recently seen a sharp rise as an illicit street drug. The potency of fentanyl means mucous membrane exposure to a small amount of the drug can expose first responders, including working canines, to accidental overdose. Naloxone, a fast-acting opioid antagonist administered intranasally (IN) or intramuscularly (IM) is currently carried by emergency personnel in the case of accidental exposure in both humans and canines. Despite the fact that law enforcement relies heavily on the olfactory abilities of canine officers, the effects of fentanyl exposure and subsequent reversal by naloxone on the olfactory performance of canines are unknown. In a block-randomized, crossover trial, we tested the effects of IN and IM naloxone on the abilities of working dogs to recognize the odor of Universal Detection Calibrant (UDC) prior to, and two, 24, and 48 h after intravenous fentanyl sedation and naloxone reversal. No detectable influence of fentanyl sedation and naloxone reversal on the dogs’ olfactory abilities was detected. We also found no difference in olfactory abilities when dogs received IN or IM naloxone. Together, results suggest no evidence that exposure to intravenous fentanyl followed by naloxone reversal impairs canine olfactory ability under these conditions.
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Canine sports medicine and rehabilitation recently have evolved to embody the optimization of performance, injury prevention, and mitigation of musculoskeletal degeneration. This article discusses the diverse factors and considerations of working dog wellness and injury prevention and the importance of recognizing normal and abnormal posture and anatomic structure for performance evaluation and early indication of musculoskeletal injury. The importance of a canine physical fitness program is highlighted and the need for a 4-phase recovery plan to determine if a working dog can safely return to work after injury discussed.
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Experiments were conducted to assess whether changing dietary fat composition altered phospholipid composition of rat testicular plasma membranes in a manner that altered receptor-mediated action of luteinizing hormone (LH)/human chorionic gonadotropin (hCG). Weanling rats were fed diets that provided high or low cholesterol intakes and that were enriched with linseed oil, fish oil or beef tallow for 4 wk. Feeding diets high in (n-3) fatty acids decreased plasma and testicular plasma membrane 20:4(n-6) content. A marked reduction of the 22:5(n-6) content and an increase in the 22:6(n-3) content of testicular plasma membrane was found only in animals fed fish oil. A decrease in binding capacity of the gonadotropin (LH/hCG) receptor in the plasma membrane, with no change in receptor affinity, was observed for animals fed either linseed oil or fish oil diets. Dietary treatments that raised plasma membrane cholesterol content and the cholesterol to phospholipid ratio in the membrane were associated with increased binding capacity of the gonadotropin receptor. Feeding diets high in 18:3(n-3) vs. those high in fish oil altered receptor-mediated adenylate cyclase activity in a manner that depended on the level of dietary cholesterol. Feeding diets high in cholesterol or fish oil increased basal and LH-stimulated testosterone synthesis relative to that in animals fed the low cholesterol diet containing linseed oil. It is concluded that changing the fat composition of the diet alters the phospholipid composition of rat testicular plasma membranes and that this change in composition influences membrane-mediated unmasking of gonadotropin receptor-mediated action in testicular tissue.
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The effects of dietary olive oil, corn oil and medium-chain triglycerides (MCT) on factors that characterized erythrocyte membrane lipid fluidity were studied. Weanling rats were fed for 3 or 5 wk high fat diets (10%) containing olive oil, corn oil or a mixture of MCT with olive oil or corn oil. Total phospholipids and phosphatidylcholine of erythrocyte ghosts obtained from olive oil-fed animals, as compared to those fed corn oil, showed an increase in long-chain polyunsaturated fatty acids (PUFA) of the (n-6) and (n-3) series and a decrease in saturated fatty acids. The addition of MCT to the olive oil diet induced an increase in palmitic, palmitoleic and delta-5,8,11-eicosatrienoic acids and a decrease in long-chain PUFA of the (n-6) series in erythrocyte membrane phospholipids. Conversely, rats fed a mixture of MCT and corn oil, as compared to those fed exclusively corn oil, showed increase in long-chain PUFA of the (n-6) and (n-3) series, with no changes in saturated fatty acid levels. The cholesterol/phosphorus molar ratio showed only a slight increase with MCT supplementation. Olive oil feeding induced important changes in fatty acid composition of erythrocyte membrane phospholipids as compared to corn oil feeding without modifying the cholesterol/phosphorus ratio and MCT feeding slightly affected red blood cell membrane lipid composition.
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Twenty-four (24) mature, mixed breed, healthy dogs weighing from 14.6 kg to 27.6 kg were used to study the effects of various steroids on the olfactory function of the dog using olfactory detection threshold as an index. Two odorants were used, viz; benzaldehyde and eugenol. Of the various steroids used, only dexamethasone produced classical signs of Cushing's syndrome in the dogs. However, all dogs that received either dexamethasone alone or hydrocortisone plus DOCA exhibited a significant elevation in the olfactory detection threshold for both odorants without any observable structural alteration of the olfactory tissue using light microscopy. On the other hand, neither DOCA, hydrocortisone alone, nor any of the vehicles used in the study significantly altered the olfactory function of the dogs. The results show that Cushing's syndrome can be experimentally produced in dogs using exgenous steroids and that this condition diminishes the olfactory capability of the dog without producing classical signs of the disease.
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The ability of human subjects to detect α-ionone was measured over a range of concentrations and compared with that of German Shepherd dogs measured previously under comparable conditions. The mean minimal concentration detected by humans was 4.0×109 molecules / cm3 which compares with a mean minimal concentration of 4.0×105 molecules / cm3 for the dogs. In general, dogs could detect α-ionone in concentrations 1,000 to 10,000 times lower than could human subjects. Concentration-response curves for both species are similar in form and show a double reversal in their upper ranges.
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The effects of dietary fatty acids on serum and cutaneous fatty acids of healthy dogs were evaluated under controlled conditions. Beagle puppies (n = 12) were fed a standard diet supplemented with sunflower oil (group A), olive oil (group B) or no supplementation (group C) for 12 weeks. There were no significant differences in food intake or growth rates between the three groups. Dogs in group A had significant increases (P < 0.05) in serum 18:2n6 (linoleic acid) and 20:3n6 (dihomo-gamma-linolenic acid), and cutaneous 18:2n6 with significant decreases in serum 20:4n6 (arachidonic acid) and cutaneous 18:1n9 (oleic acid) and 18:3n3 (alpha-linolenic acid). Dogs in group B had significant increases in serum 18:1n9, 20:3n6 and cutaneous 18:1n9 with decreases in serum 20:4n6, 22:4n6, 22:5n3 and 22:5n6, and cutaneous 18:2n6, 18:3n3 and 20:4n6. There were no significant changes in serum or cutaneous fatty acids for the dogs in group C. This study demonstrates that fatty acid supplements can be used to alter the serum and cutaneous fatty acid compositions of dogs.
Article
Muscle glycogen and plasma glucose are oxidized by skeletal muscle to supply the carbohydrate energy needed to exercise strenuously for several hours (i.e., 70% maximal O2 consumption). With increasing exercise duration there is a progressive shift from muscle glycogen to blood glucose. Blood glucose concentration declines to hypoglycemic levels (i.e., 2.5 mmol/L) in well-trained cyclists after approximately h of exercise and this appears to cause muscle fatigue by reducing the contribution of blood glucose to oxidative metabolism. Carbohydrate feeding throughout exercise delays fatigue by 30-60 min, apparently by maintaining blood glucose concentration and the rate of carbohydrate oxidation necessary to exercise strenuously. Carbohydrate feedings do not spare muscle glycogen utilization. Very little muscle glycogen is used for energy during the 3-4-h period of prolonged exercise when fed carbohydrate, suggesting that blood glucose is the predominant carbohydrate source. At this time, exogenous glucose disposal exceeds 1 g/min (i.e., 16 mg.kg-1.min-1) as evidenced by the observation that intravenous glucose infusion at this rate is required to maintain blood glucose at 5 mmol/L. However, at this time these cyclist cannot exercise more intensely than 74% of maximal O2 consumption, suggesting a limit to the rate at which blood glucose can be used for energy. It is important to realize that carbohydrate supplementation during exercise delays fatigue by 30-60 min, but does not prevent fatigue. In conclusion, fatigue during prolonged strenuous exercise is often due to inadequate carbohydrate oxidation. This is partly a result of hypoglycemia, which limits carbohydrate oxidation and causes muscle fatigue.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
The need to evaluate sensory function in the dog is discussed. A group of techniques that use innate behaviors (species-typical behaviors) and are effective in the evaluation of sensory function of domestic animals are described. Techniques to measure olfactory, gustatory, auditory, and visual function are included.
Article
It is clear from this review that olfactory function is markedly altered in old age and in a number of age-related diseases. The deficits appear to be rather general and detectable by several types of olfactory tests. Considerable interindividual variability exists, however, and the physiologic bases of these changes are not clear. In many healthy elderly persons, smell loss appears to occur as a result of one or more causes, including viral insult, cumulated exposure to toxic fumes, head trauma, and calcification of the cribriform plate. Several reviews have appeared suggesting that the olfactory system may be a center of primary involvement in AD. Of particular interest is the hypothesis that environmental agents (related etiologically to the disease process) pass into the central nervous system via the highly active transport mechanisms of the olfactory receptors. This latter notion, although attractive, must be viewed conservatively, as it is possible that the olfactory pathways are simply selectively vulnerable to destruction by various disease processes. This may explain why Huntington's chorea and multiinfarct dementia, in addition to AD and PD, are associated with alterations in smell function. Although it is tempting to assume, as have authors such as Koss et al., that alterations in threshold function reflect peripheral olfactory dysfunction and that alterations in odor identification and other more demanding tasks reflect central olfactory dysfunction, there is little empirical support for such a simple dichotomy. Despite the fact that a peripheral/central distinction is useful in clinical audiology (where threshold loss is commonly associated with CN VIII pathology), an evaluation of the utility of this distinction in olfaction requires further research. The limited data suggest that both identification and detection deficits commonly arise from damage to the olfactory epithelium, even though identification deficits unassociated with detection deficits may occur in some central brain disorders. It is apparent from the studies reviewed in this chapter that considerable progress has been made during the last decade in elucidating the nature and prevalence of olfactory disturbances in elderly patients, as well as in patients with dementia-related diseases.(ABSTRACT TRUNCATED AT 400 WORDS)
Article
Olfactory function of 5 dogs that were naturally infected with canine parainfluenza virus and of 4 dogs that were inoculated with the C958 strain of canine parainfluenza virus was evaluated. Except for one dog that was inoculated, the threshold for detection of benzaldehyde and/or eugenol was found to be excessively high during the course of the disease, as determined by electroencephalographic and behavioral olfactometry. In experimentally infected dogs, an increase in threshold developed in the absence of other clinical signs of disease. Changes were not observed in electro-olfactograms recorded throughout the study. Olfactory thresholds returned to normal after the disappearance of clinical signs of disease in the naturally infected dogs. Necropsies and histologic examinations performed during the course of the disease did not reveal abnormalities of the olfactory mucosa.