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Short-duration exercise and confinement alters bone mineral content and shape in weanling horses


Abstract and Figures

The hypothesis that short-duration exercise may ameliorate the decrease in bone mass observed with confinement was investigated with 18 quarter horses (nine colts and nine fillies) weaned at 4 mo of age and placed into box stalls. After a 5-wk adjustment period, individuals were grouped by age and weight, and then divided randomly into three treatment groups: 1) group housed; 2) confined with no exercise; and 3) confined with exercise. The confined and exercised groups were housed in 3.7 m x 3.7 m box stalls for the 56-d duration of the trial. The exercised group was sprinted 82 m/d, 5 d/wk, in a fenced grass alleyway. The weanlings were led down an alleyway, turned loose in a small pen, and then released and allowed to run back down the alley. The group horses were housed together in a 992-m2 drylot with free access to exercise. On d 0, 28, and 56, dorsopalmar and lateromedial radiographs of the left third metacarpal bone were taken to estimate changes in bone mineral content and cortical widths. Mean values of medial, lateral, and total radiographic bone aluminum equivalence increased over time (P < 0.05), whereas dorsal and palmar radiographic bone aluminum equivalence did not change significantly. Dorsal, medial, and total radiographic bone aluminum equivalence tended (P = 0.09) to differ by a treatment x day interaction, with values increasing over time only in the exercised group. Normalized medial and total radiographic bone aluminum equivalence tended (P < 0.1) to differ (P < 0.01) with treatment, with exercised horses having greater bone aluminum equivalence than confined horses. Dorsopalmar cortical width in exercised horses was greater than on d 56 (treatment x day; P = 0.07). The dorsopalmar medullary cavity decreased in exercised vs. group-housed horses (P = 0.027), whereas dorsal and medial cortical width tended to increase only in the exercised horses (treatment x day; P < 0.01). This study indicated that a short-duration exercise protocol might be effective in improving bone mass and therefore skeletal strength in horses.
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Short-duration exercise and confinement alters bone mineral content
and shape in weanling horses
K. M. Hiney*
, B. D. Nielsen*, and D. Rosenstein†
*Department of Animal Sciences and †Department of Large Animal Clinical Medicine,
Michigan State University, East Lansing 48824-1225
ABSTRACT: The hypothesis that short-duration ex-
ercise may ameliorate the decrease in bone mass ob-
served with confinement was investigated with 18 quar-
ter horses (nine colts and nine fillies) weaned at 4 mo of
age and placed into box stalls. After a 5-wk adjustment
period, individuals were grouped by age and weight,
and then divided randomly into three treatment groups:
1) group housed; 2) confined with no exercise; and 3)
confined with exercise. The confined and exercised
groups were housed in 3.7 m × 3.7 m box stalls for
the 56-d duration of the trial. The exercised group was
sprinted 82 m/d, 5 d/wk, in a fenced grass alleyway.
The weanlings were led down an alleyway, turned loose
in a small pen, and then released and allowed to run
back down the alley. The group horses were housed
together in a 992-m
drylot with free access to exercise.
On d 0, 28, and 56, dorsopalmar and lateromedial radio-
graphs of the left third metacarpal bone were taken to
estimate changes in bone mineral content and cortical
widths. Mean values of medial, lateral, and total radio-
Key Words: Bone, Confinement, Equine, Exercise, Growth
2004 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2004. 82:2313–2320
Injuries to the skeletal system of the horse are a
concern to the equine industry. Early training in young
horses may be beneficial to the longevity of their ca-
reers. In Australia, horses receiving their first starts
as 2-yr-olds had more starts and raced longer than those
that began their racing careers at a later age (Bailey
et al., 1999). The early training that these horses re-
ceived in preparation to race as 2-yr-olds may have
aided in modeling the skeleton for high-speed activity.
Most studies show that the greatest skeletal adapta-
tions occur in very young animals or humans (Loitz and
Zernicke, 1992; Umemura et al., 1995; Iwamoto et al.,
Correspondence: 410 S. Third St., River Falls, WI 54022 (phone:
715-425-3704; fax: 715-425-3785; e-mail:
Received January 3, 2004.
Accepted April 14, 2004.
graphic bone aluminum equivalence increased over
time (P < 0.05), whereas dorsal and palmar radio-
graphic bone aluminum equivalence did not change sig-
nificantly. Dorsal, medial, and total radiographic bone
aluminum equivalence tended (P = 0.09) to differ by a
treatment × day interaction, with values increasing
over time only in the exercised group. Normalized me-
dial and total radiographic bone aluminum equivalence
tended (P < 0.1) to differ (P < 0.01) with treatment,
with exercised horses having greater bone aluminum
equivalence than confined horses. Dorsopalmar cortical
width in exercised horses was greater than on d 56
(treatment × day; P = 0.07). The dorsopalmar medullary
cavity decreased in exercised vs. group-housed horses
(P = 0.027), whereas dorsal and medial cortical width
tended to increase only in the exercised horses (treat-
ment × day; P < 0.01). This study indicated that a short-
duration exercise protocol might be effective in improv-
ing bone mass and therefore skeletal strength in horses.
2000). Thus, if horses received exercise at an earlier
age, well before traditional training began, greater ben-
efits to the skeletal integrity of the horse may be seen.
Exercise bouts need not be of lengthy duration, pro-
vided an effective stimulus level on the bone is reached
(Rubin and Lanyon, 1984; Inman et al., 1999). Four
cycles per day of an externally applied force prevented
bone loss in immobilized turkey ulnae (Lanyon, 1984)
and five jumps per day increased bone mass and me-
chanical strength of rat femora and tibiae over seden-
tary controls (Umemura et al., 1997). Although no de-
finitive magnitude of strain to cause bone adaptation
has been described for all species, sprinting 50 m, 5 d/
wk, for 6 wk enhanced bone geometry in immature
calves (Hiney et al., 2004). No studies of the strain
magnitude experienced in the metacarpal bone of im-
mature calves have been performed, but galloping in
horses creates high strain magnitudes in the third
metacarpal bone (3,200 microstrains; Rubin, 1984).
Thus, only a few cycles, corresponding to strides, should
Hiney et al.2314
be necessary to elicit an osteogenic response, especially
in an immature animal. Therefore, a protocol similar
to that of Hiney et al. (2004), featuring short bouts of
sprinting exercise 5 d/wk, was implemented in an
equine study to test if this species would respond in a
similar manner.
Materials and Methods
Animals and Management
Eighteen quarter horses, nine colts and nine fillies,
were weaned at approximately 4 mo of age. Horses were
weaned by removal from their dams and placement into
box stalls (3.7 m × 3.7 m). The foals remained in the
stalls for 5 wk before the initiation of the study. Stress
due to weaning temporarily decreases feed intake and
thus slows growth (Knight and Tyznik, 1985); therefore,
this time period allowed the foals to adjust from the
stress of weaning as well as to adapt to handling. Foals
were fed alfalfa hay and a commercially available pel-
leted concentrate in a 50:50 ratio at 2 to 2.5% BW (Strat-
egy Professional Formula GX, Purina Mills LLC, St.
Louis, MO) to maintain body condition. The study was
conducted in the summer, with the horses housed out-
side exposed to natural photoperiod, whereas the
stalled horses received 16 h/d of artificial light. Individ-
uals were stratified according to age, weight, and gen-
der, and then randomly assigned to one of three treat-
ments resulting in six horses per treatment: 1) confined
without exercise (CF), 2) confined with exercise (EX),
and 3) group housed (GR). The average weight of the
horses was 226 ± 4 kg and the average age was 165 d.
The GR horses were housed together in a 992-m
drylot with free access to exercise. The CF horses re-
mained in box stalls for the 8-wk duration of the project
with no access to exercise, whereas the remaining EX
horses received forced exercise 5 d/wk. The exercise
protocol was moderate, requiring the horses to gallop
82 m over a turf surface. The EX horses were led from
their stalls to the end of an 82-m grass alleyway and
turned loose in a small pen. Horses were then released
from the pen, galloped down the alleyway back toward
the barn, and were caught in a small pen at the end of
the alley. The speed of the horses averaged between 6
to 8 m/s accounting for acceleration and deceleration.
Only on very infrequent occasions did the foals fail to
gallop up the length of the alley when released. The
horses were returned to their stalls, with the entire
distance traveled being approximately 264 m, including
the distance walked from the barn to the alleyway.
Behavior Observations
Observations of behavior were made over 24 h on d
0, 28, and 56 for all groups. Horses were kept under
constant lighting and videotaped in either their box
stalls or in the group drylot with an extended cam-
corder, which recorded 24 h on one tape. For all horses,
four separate hours of each 24-h period were randomly
chosen for each horse for observation, and then 15 min
of each hour were analyzed. Behavior observations were
limited to activities that would load the bone and there-
fore affect bone strength. Durations of behaviors were
recorded and summed for each 15-min period. The total
duration of the behaviors was recorded as a proportion,
or percentage, of time for which all occurrences of the
behavior lasted over the observation session. The total
duration of behaviors was summed for each observation
day and over all three days. These behaviors included
bouts of standing, walking, lying down, and trotting.
In addition to the behaviors recorded as cumulative
intervals, the frequency or number of occurrences of
shifting of stance from lying to standing, walking bouts,
pawing, startling (reaction in response to a sudden and
novel stimulus), and jumping were recorded for each
15-min period.
Sample Collection
Radiographs were taken at d 0, 28, and 56 to deter-
mine radiographic bone aluminum equivalence
(RBAE) values, measures of optical density and a re-
flection of bone mineral content (Meakim et al., 1981).
Only the left metacarpal bone (MCIII) was radio-
graphed for determination of bone mineral content as
other studies in mature horses have reported no differ-
ence in bone properties between forelimbs (Glade, 1993;
Lawrence et al., 1994). Radiographs of the dorsal-pal-
mar and medial-lateral views of MCIII were taken at
a focal length of 77 cm and an exposure of 65 kVp (peak
kilovoltage) (25 mA for 0.1 s). An aluminum stepwedge
was attached to the radiographic cassette to standard-
ize readings and to calculate RBAE values. Horses were
also weighed on a livestock scale on d 0, 28, and 56.
Radiographic Bone Aluminum Equivalence
Optical density of the bone was assessed using radio-
graphic photodensitometry to determine RBAE using
a Bio-Rad (Hercules, CA) model GS 700 imaging densi-
tometer (Bell et al., 2001). Radiographs were scanned
3 mm distal to the nutrient foramen of MCIII with
Multi-Analyst software (Bio-Rad), a software package
designed to translate digital images into numerical
data. A linear regression was created by plotting the
optical density of the scanned image of the aluminum
penetrometer against the known thickness of the steps.
Maximum optical density of each cortex was expressed
in millimeters of aluminum for both cortices in each
view of MCIII. Total RBAE was measured by taking the
area under the curve of the bone scan and expressing it
in relation to a known volume of aluminum calculated
from the area of the scanned image of the stepwedge
(Nielsen and Potter, 1997).
Cortical Widths
The dorsal-palmar radiographic view was used to
measure the width of the medial and lateral cortices,
Exercise and confinement alters bone shape 2315
Figure 1. Schematic illustration of a cross-section of
bovine third and fourth metacarpal showing cortical mea-
surements. B = outside major diameter (lateromedial bone
diameter); b = inside major diameter (lateromedial med-
ullary diameter); D = outside minor diameter (dorso-
palmar bone diameter); d = inside minor diameter (dorso-
palmar medullary diameter).
the inner medullary diameter, and the outer cortical
diameter (Figures 1 and 2). The beginning of the curve
of the bone image, as developed by the Multi-Analyst
software, to the highest point of the curve was measured
for the width of each individual cortex, and the medul-
lary diameter (or medullary cavity) was measured from
the distance between the two peaks of the curve. The
outer cortical diameter was measured as the entire dis-
Figure 2. Schematic illustration of a cross-section of
equine third metacarpal showing cortical measurements.
DC = dorsal cortical width; PC = palmar cortical width;
MC = medial cortical width; LC = lateral cortical width.
Figure 3. Schematic illustrations of cortical measure-
ments created from Multi-Analyst software. a = bone di-
ameter; b = medullary diameter; c and c’ = individual
cortical diameters.
tance of the curve (Figure 3). The similar procedure
was used for the lateromedial view for determination
of dorsal and palmar cortical widths, and the inner
medullary diameter and outer cortical diameter across
the dorsopalmar aspect of the bone.
Statistical Analysis
Statistical analysis of RBAE and cortical widths was
performed using the MIXED procedure of the SAS (SAS
Inst., Inc., Cary, NC) with a covariance test suitable
for repeated measures. The covariance structure was
first-order autoregressive, with horse within treatment
used as the subject effect. The model tested for treat-
ment, day, and the treatment × day interaction. When
main effects were significant, post hoc comparisons
were used to separate differences between means. Least
squares means were separated by the Tukey’s method.
Individual standard errors of the mean for each treat-
ment are included in the tables and figures. To aid in
visualizing changes over time within an individual,
data were also normalized by subtracting d-0 values
from all subsequent values. Behavior data were ana-
lyzed with a multinomial distribution, which predicted
the probability of behavior occurrence between groups.
Frequency behaviors, such as postural shifts, walking
bouts and pawing, were analyzed using a Poisson distri-
bution. For all analyses, P-values less than 0.05 were
considered significant, whereas P-values less than 0.10
were discussed as trends.
As horses were assigned to treatments according to
weight, BW were similar at the initiation of the study
(226, 226, and 227 ± 4 kg for EX, CF, and GR respec-
tively) and remained similar throughout the study with
final weights of 270, 269, and 263 ± 3 kg for EX, CF,
and GR horses.
Hiney et al.2316
Table 1. Mean radiographic bone aluminum equivalence (mm Al) of the third metacarpal
bone as affected by exercise, confinement, or group housing over the 56-d trial
Exercised Confined Group
Variable d 0 d 28 d 56 d 0 d 28 d 56 d 0 d 28 d 56 SEM
Dorsal 15.0
15.5 15.6 15.7 15.6 15.3 15.3 0.10
Palmar 14.6 14.3 14.7 15.1 14.7 14.6 15.3 14.9 14.8 0.12
16.9 18.9 18.9 17.3 17.9 18.9 17.8 17.5 19.0 0.20
15.6 17.2 18.1 16.6 17.1 18.0 16.5 16.8 18.1 0.20
186 156 224 176 170 184 11.24
SEM, pooled across treatments within day were as follows: 0.2 mm for dorsal on each day; 0.2 mm for
palmar on each day; 0.2, 0.3, and 0.4 mm for medial on d 0, 28, and 56, respectively; 0.3 mm for lateral on
each day; and 15, 13, and 25 mm for total on d 0, 28, and 56, respectively.
Means pooled across treatments for d 0, 28, and 56 differed (P < 0.05).
Means pooled across treatments for d 0 and 28 differed from d 56 (P < 0.05).
Different superscripts indicate a trend (P < 0.10) for treatment × day interactions in exercised hoses
Radiographic Bone Aluminum Equivalence
Dorsal and palmar RBAE values did not differ ac-
cording to time or treatment, but there was a trend for
a treatment × day interaction (P = 0.09) in the dorsal
cortex, with values increasing to d 56 only in the EX
group (Table 1). The dorsal cortex of MCIII in the CF
and GR animals remained essentially unchanged from
the initiation of the trial. Although overall dorsal and
palmar values did not increase over time, overall medial
and lateral RBAE values increased significantly over
the duration of the study (P = 0.001 and P = 0.001, re-
When treatment means were separated, the only in-
crease in medial RBAE was in the EX group (treatment
× day interaction; P = 0.055), similar to that seen in
the dorsal RBAE data. Total RBAE also increased over
time (P = 0.003) and, comparable to both dorsal and
medial RBAE data, when means were separated, total
RBAE values tended to increase only in the EX animals
(P = 0.087). When total RBAE values were normalized,
there was a significant effect (P = 0.020) of treatment,
with values for EX horses increasing more (137 ± 44
Al) than those for either CF (38 ± 40) or GR horses
(8 ± 25).
Cortical Widths
Dorsopalmar cortical diameter increased over time
(P = 0.001; Table 2), with values on d 56 greater than
eitherd0ord28.Inaddition, there was a trend for
EX to be greater than GR on d 56 (treatment × day;
P = 0.07). Both CF and EX had greater dorsopalmar
bone diameters on d 56 in comparison with d 28. When
data were normalized by examining the changes in val-
ues from d 0, the treatment × day interaction was sig-
nificant, as EX had increased by 2.3 mm (P = 0.07), CF
had increased by 1.7 mm (P = 0.02), and GR did not
change (P = 0.91). Overall, the medullary dorsopalmar
diameters did not change over the duration of the trial,
but treatment × day interactions were significant (P =
0.018). When data were normalized, the medullary cav-
ity decreased in EX (1.5 mm) compared with GR, which
gained slightly (0.2 mm; P = 0.027). The change in
medullary diameter of CF was not different from either
EX or GR.
Dorsal cortical width averaged over all treatments
did not change over time, but a trend for an increase
did occur in EX (treatment × day; P = 0.01). When dorsal
cortical width was normalized in relation to d 0, EX
was greater than both CF and GR (P = 0.011). The
average change in the EX was 2.0 mm vs. 0.2 mm in
CF and 0.3 mm in the GR foals. Palmar cortical widths
tended (P = 0.08) to increase over time but did not differ
between treatments.
The lateromedial bone diameter increased over time
(P = 0.001) but was not different between treatments
(Table 3). Mean medial and lateral cortical widths in-
creased over time (P = 0.003 and P = 0.036, respec-
tively), and in the normalized medial widths, EX tended
to gain more width in the medial cortex (2.1 mm) com-
pared with GR (0.4 mm) (P = 0.09). Finally, the lateral
cortex was not different by treatment.
The percentage of observed time spent walking aver-
aged over all days did not differ between treatments
(2.3 and 2.8% for EX and CF, respectively), with the
GR horses averaging slightly more walking at 5% of
the observed time. The EX foals spent less time stand-
ing (64% of the observed time) compared with the CF
(78%) and GR (84%; P = 0.004) foals. The EX foals spent
a greater proportion of time (34%) lying down compared
with CF (20%) or GR (12%; P = 0.001) foals. The inci-
dence of pawing in the CF foals was greater (Table 4;
P = 0.001) than in EX or GR. The frequency in shifting
stance between standing and lying was greater in CF
foals than in GR foals (P = 0.011). The number of walk-
ing bouts did not differ among treatments. As animals
were never observed startling or jumping during the
observation periods, these behaviors were not reported
in the tables. The occurrence of trotting bouts was very
infrequent. Thus, duration of trotting was very short
Exercise and confinement alters bone shape 2317
Table 2. Mean dorsopalmar cortical diameters (mm) of the third metacarpal bone as
affected by exercise, confinement, or group housing over the 56-d trial
Exercised Confined Group
d0 d28 d56 d0 d28 d56 SEM
Dorsopalmar o.d.
26.9 27.3 27.2 0.26
Dorsopalmar i.d. 15.0 14.2 13.5 14.1 13.3 14.2 13.7 14.4 13.9 0.20
Dorsal cortex 7.7
8.1 9.8 8.5 8.6 8.7 8.5 8.3 8.2 0.20
Palmar cortex 4.7 4.9 5.9 4.8 51 5.8 5.1 5.1 5.0 0.13
SEM, pooled across treatments within day were as follows: 0.4, 0.4, and 0.5 mm for dorsopalmer o.d. on
d 0, 28, and 56, respectively; 0.4, 0.3, and 0.3 mm for dorsopalmer i.d. on d 0, 28, and 56, respectively; 0.3,
0.3, and 0.4 mm for dorsal cortex diameter on d 0, 28, and 56, respectively; and 0.2 mm for palmer cortex
diameter on each day.
Means pooled across treatments differed on d 0, 28, and 56 (P < 0.05).
Indicates a trend for means to be greater in exercised horses than in group-housed horses on d 56 (P =
Means within a cortical measurement and within a treatment with different superscripts indicate a
trend (P < 0.10) for treatment × day interactions.
and did not provide sufficient data for statistical analy-
sis; therefore, these data were not reported.
Many studies of weanling and yearling horses have
shown an increase in RBAE values over time, with
increasing mineralization of the skeleton occurring
with maturation (Buckingham and Jeffcott, 1987; Raub
et al., 1989; McCarthy and Jeffcott, 1992) and the ma-
jority of increase in mineral content of the young horse
limited to the first year and a half of life (Nielsen et
al., 1997; Hiney, 1998). In the current study, medial,
lateral, and total RBAE values increased in all groups
over 56 d, but dorsal or palmar RBAE values did not
The increase in RBAE may not have been due solely
to increased density, but rather to the normal expansion
of MCIII with growth. One of the difficulties in de-
termining changes in mineralization with radiographic
photodensitometry is that this technique does not spe-
cifically measure density. As the animal grows, bone
increases in size; thus, the x-rays pass through a thicker
Table 3. Mean lateromedial cortical diameters (mm), as affected by exercise, confinement,
or group housing over the 56-d trial
Exercised Confined Group
Variable d 0 d 28 d 56 d 0 d 28 d 56 d 0 d 28 d 56 SEM
Lateromedial o.d.
35.0 35.9 38.3 35.2 35.5 38.1 34.7 35.9 36.3 0.39
Lateromedial i.d. 22.4 22.2 21.1 21.8 21.4 21.5 21.0 20.9 20.4 0.37
Medial cortex
7.0 8.1 9.1 6.9 7.4 7.9 7.5 8.0 7.9 0.18
Lateral cortex
6.8 7.1 7.4 7.2 7.1 8.0 6.5 7.7 7.7 0.15
SEM, pooled across treatments within day were as follows: 0.7, 0.7, and 0.6 mm for lateromedial o.d. on
d 0, 28, and 56, respectively; 0.7, 0.7, and 0.5 mm for lateromedial i.d. on d 0, 28, and 56, respectively; 0.3
mm for medial cortex diameter on each day; and 0.2, 0.3, and 0.3 mm for lateral cortex diameter on d 0,
28, and 56, respectively.
Means pooled across treatment on d 0, 28, and 56 differed (P < 0.05).
Means pooled across treatment for d 0 differed from d 28 and 56 (P < 0.05)
Means pooled across treatments for d 0 differed from d 56 (P < 0.05). Means for d 28 were not different
(but not necessarily denser) tissue, thereby appearing
denser on the film.
Because the largest recorded strains during galloping
occur in the dorsal and medial cortex of MCIII (Gross
et al., 1992), exercise typically causes greater mineral-
ization to occur in the dorsal and medial cortex. Al-
though overall medial and total RBAE values increased
over time, only the EX group showed increased medial,
dorsal, and total RBAE values, as shown by post hoc
analysis. Although only trends, the short-term exercise
seemed to cause more mineral deposition in those areas
of the bone experiencing the most strain during gallop-
ing. Again, these changes may have been due to the
formation of new bone rather than increased mineral-
ization of preexisting bone.
One of the greatest adaptations created by exercise
is in the geometry of bone. Therefore, a method of mea-
suring widths from the radiographic image of the bone
scanned into the Multi-Analyst software was used to
analyze geometry. The main effects of growth in 56 d
appear to be more related to the size and shape of the
bone than to density. Whereas only EX group showed
increases in dorsal, medial, and total RBAE, the CF
Hiney et al.2318
Table 4. Total number of occurrences of behaviors
summed over all observations and days for each treat-
ment group
No. of occurrences
Variable Exercised Confined Group
Paw 13
Walking bouts 315 410 288
Stance change 10
Treatment values that do not have common superscripts differ
(P < 0.05).
and EX groups experienced increased dorsopalmar bone
diameters, and all three treatments resulted in in-
creased medial and lateral cortical widths and later-
omedial bone diameter over the 56 d when data were
averaged together. However, the tendency of the EX
group to show an increase in mineral content was re-
flected in changes in width in the same aspects of the
Changes in the shape of the bone may be the domi-
nant loading adaptation that occurs during early life,
and the changes in the shape of MCIII may be the best
indicator of increased mechanical integrity. The total
circumference of the bone (as estimated from measuring
across the lateromedial and dorsopalmar widths of the
bone) increased in all groups over the 56 d of the trial,
indicating normal periosteal expansion with growth re-
ported previously (Buckingham and Jeffcott, 1987).
Periosteal expansion in the dorsopalmar direction was
greater in EX in relation to GR, and normalized data
showed both CF and EX to be greater than GR. Al-
though no mechanical testing was performed in this
study, others have shown that stiffness of equine bone
increases with increased bone diameter (Hanson et al.,
1995). As the moment of inertia varies with the fourth
power of the outer diameter of the bone, the EX horses
with greater bone diameter may potentially be at a
mechanical advantage.
The size of the medullary cavity did not change with
time, but endosteal expansion may not occur until later
in skeletal development. Even so, in the normalized
data, the EX group tended to have a smaller medullary
cavity than did the GR group. Whether this was because
of a contraction of the endosteal space due to exercise
or an expansion of the endosteal space in GR horses is
impossible to determine without the aid of histomorpho-
metric studies.
Medial and lateral cortical widths increased signifi-
cantly over time in all horses, but palmar cortical width
only tended to increase. Normalized medial cortical
width also showed a trend for an increase in EX vs. GR
horses. Whereas dorsal cortical width averaged across
all 18 horses did not change, the mean of the EX group
tended to increase. Therefore, the exercise protocol
seemed to be causing some adaptation of MCIII, but
usually only in comparison to the GR horses. Why the
GR horses would have shown less periosteal expansion
than either of the box-stalled groups, especially as they
underwent no less activity than that performed by the
CF horses, is unclear.
Although the estimation of cortical widths from radio-
graphic images is not as precise as data that can be
obtained from modalities such as computed tomogra-
phy, it at does provide an additional tool to monitor
changes in bone that may not be related to density or
mineral content changes. In the young animal, adapta-
tion of the architecture of bone is the predominant re-
sponse to exercise. Exercise increased the dorsal perios-
teal apposition rate in young Thoroughbreds (McCarthy
and Jeffcott, 1991, 1992). Race training also increased
dorsal, medial, and lateral cortical diameters, as well
as dorsopalmar and lateromedial widths, and decreased
the size of the medullary cavity, similar to the results
here (Thomson et al., 2001). Thus, the data, while only
showing trends for improvement in the EX, corresponds
with alterations in bone geometry due to exercise pre-
viously reported in horses.
In addition, the foals receiving the short-term exer-
cise responded in a manner comparable to calves per-
forming a similar exercise program (Hiney et al., 2004).
Running 50 min, 5 d/wk, resulted primarily in a change
in bone shape of the fused third and fourth metacarpal
bone. Exercise decreased the size of the medullary cav-
ity and increased the dorsal cortical width compared
with calves kept in confinement or those allowed free
access to exercise, similar to the results in the horses.
However, there were differences between calves and
horses that suggest, while similar, these two species
do not adapt to exercise in an identical manner. The
exercised calves were not different in the dorsopalmar
bone diameter whereas the exercised horses increased
in dorsopalmar bone diameter. Conversely, the later-
omedial diameter was smaller in the exercised calves
compared with no change between groups in the equine
study. The difference in adaptation of bone shape is
most likely due to a dissimilar pattern of bone strain
in the equine MCIII compared with the fused third and
fourth metacarpal bone in the calves. Therefore, while
useful to perform preliminary studies, the calf model
may not be able to completely replace studies performed
using horses.
Stalling the weanlings for 2 mo did not result in bone
loss in CF and would not be expected in such rapidly
growing animals; however, the CF horses were not at
any disadvantage compared with the GR horses. The
behavioral observations made of the horses aid in ex-
plaining the lack of differences in bone measures be-
tween the CF horses and GR horses allowed freedom
of movement. The CF horses did not have lower RBAE
or less favorable bone geometry compared with GR.
Rather, the GR horses tended to have the lowest bone
measurements, which was unexpected, and most treat-
ment differences were seen between EX and GR. How-
Exercise and confinement alters bone shape 2319
ever, despite their greater opportunity for movement,
the GR horses did not differ in the time spent per-
forming activities that would significantly load the bone
compared with CF.
The imposed confinement did seem to increase frus-
tration in the CF horses as they pawed more than either
EX or GR horses. Presumably this was due to the in-
crease in motivation for locomotor behavior following
a period of behavior deprivation, which can lead to a
variety of abnormal behaviors or stereotypes in horses,
including pacing weaving or pawing the stall floor (Dell-
meier, 1989). In addition, the confined horses shifted
their stance between laying and standing more fre-
quently than either of the exercised groups. Even EX
horses, which were out of the boxed stalls for only a
very short time period (about 10 min), 5 d/wk, exhibited
fewer frustrated behaviors. The amount of strain on
the bone as a result of activities such as pawing is
unknown. In addition, while infrequent, the CF animals
were the only ones observed jumping or startling in
their stalls. Both of these activities have been reported
to result in very large strain magnitudes (Skerry and
Lanyon, 1995; Konieczynski et al., 1998). These infre-
quent strains may play a significant role in the adapta-
tion of bone and may explain why CF did not differ
from GR.
Results of this study seem to indicate that very short
periods of exercise increased bone mineral content and
altered bone geometry of stalled weanling horses in
comparison to those kept in small paddocks. Confine-
ment of at least an 8-wk duration did not seem to cause
any dramatic effects of disuse osteopenia; however, this
is difficult to determine without pre-weaning RBAE
values. These results are similar to those found in a
study of similar design conducted on young calves.
The results of this study indicate the potential value
of implementing an exercise program in immature
horses. By stimulating the skeleton at an early age to
model for intense activity, these animals may be better
adapted for training than those that begin training at
a later age. The exercise protocol was easy to implement
and was of minimal stress to the horses. Therefore,
similar exercise protocols might be suggested to en-
hance skeletal strength before more traditional under-
saddle training. Horses housed in pens may not have
much strain placed on bone if the area provided is not
adequate to encourage activity. The group housing used
in this study was too small and lacking in stimuli to
encourage much activity. Therefore, it is recommended
to increase the space available when a specific exercise
program is not used. Currently, more research needs
to be performed regarding the long-term benefits of such
an exercise program and the frequency with which they
should be employed.
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... For this reason, while horses are growing, their skeletal strength is highly influenced by the strains their bones undergo through daily use and exercise [19]. Short-term dynamic exercise as an adolescent can lead to beneficial changes in bone morphology, increased fracture force, and reduced fracture risk at maturity [20][21][22][23]. Factors in the strain environment of a bone that elicit remodeling responses include magnitude of strain, rate of change in strain, as well as spread of dynamic strain [24][25][26]. ...
... Walking has been shown to lead to deconditioning of bone in previously conditioned horses, as it does not provide a dynamic strain at a threshold to maintain bone content [28]. However, exercise which elicits bone formation, such as sprinting, during early training could negate the loss of bone due to confinement [20,21,23]. ...
... A compilation of studies which evaluated bone response to exercise in young animals is shown in Table 1. [20,21] Alterations to collagen turnover markers, suggesting lack of collagen synthesis in response to extensive sprints [35] Treadmill Greater impact strength of the third metacarpal [36] Greater radiographic bone density and volume by fraction [37] Pasture access Alterations to collagen turnover markers suggesting less type 1 collagen degradation [35] Greater third metacarpal circumference increased bone mineral content [38] ...
Full-text available
Conflicting research and anecdotal evidence have created disagreement among equestrians as to whether two-year-old horses should be trained and raced. The objective of this literature review is to evaluate epidemiological studies, as well as physiological data on equine bone, articular cartilage, and tendons to better determine the impact of training and racing two-year-old horses. The evaluation of numerous studies on the topic provides evidence that a horse which is trained or raced as a two-year-old has a lower risk of injury and better adapted tissues for the rigors of racing. Unfortunately, the current prolific use of pain-mitigating substances in the racing industry does place horses, including young cohorts, at greater risk of injury, and should be used with caution.
... The objective of this study was to utilize a calf model to determine the impact of diameter during circular exercise at the walk to forelimb bone and joint health in juvenile animals. Calves have been used as a model for the management and exercise of young horses successfully in previous studies [2,[23][24][25]. It was hypothesized that exercise on a smaller diameter circle would lead to increased biological markers of joint inflammation and metabolism and greater asymmetry between inside and outside forelimbs. ...
... The lack of treatment differences between cortical widths and BMD from computed tomography are not surprising. It is known that dynamic exercise, such as sprinting, leads to bone adaptations [2,24,25,33]. As has been previously determined, gait is an important factor in the response of loading during circular exercise [11]. ...
Full-text available
Circular exercise is used in many equestrian disciplines and this study aimed to determine if circle diameter impacts juvenile animal forelimb bone and joint health. On day 0, 24 calves at 9 weeks of age were assigned the following exercise treatments: small circle (12 m clockwise), large circle (18-m clockwise), treadmill, or non-exercised control. Exercise was initiated at 1.1–1.5 m/s for 5 min/d and increased 5 min weekly until reaching 30 min/d. On day 49, synovial fluid was collected from multiple joints, cartilage was collected from the proximal surface of fused third and fourth metacarpi (MC III and IV), and forelimbs underwent computed tomography scans. A statistical analysis (PROC mixed) was performed in SAS 9.4. The inside leg of the small circle treatment had a larger MC III and IV dorsopalmar external diameter than the outside (p = 0.05). The medial proximal phalanx had a greater mediolateral diameter than the lateral proximal phalanx of the small circle treatment (p = 0.01). Fetlock nitric oxide was greater in the large circle and treadmill treatments (p < 0.0001). Cartilage glycosaminoglycan concentration was greater in the outside leg of the small circle exercise treatment than the inside leg (p = 0.03). Even at slow speeds, circular exercise diameter can impact joint and bone health, but faster speeds may have greater alterations.
... Horses housed on pasture, especially mature horses and when temperatures are high, may choose not to exercise at an intensity that will increase BMC as expected. Hiney et al [23] found no difference in activity between confined and group housed weanlings, and Spooner et al [24] found no differences in BMC between horses receiving endurance exercise but housed in a small dry lot and horses on pasture. These previous studies support the idea that while giving horses access to turnout can negate the negative effects of stalling [25], horses housed entirely on pasture may not choose to be any more active than they are in confinement. ...
... As a measure of osteoblast activity, OC concentrations in mature horses remain relatively low with little variation [29]. Other studies that saw differences in OC concentrations between treatments used young, growing horses which naturally have higher OC concentrations and are more prone to changes in those concentrations [21,23,25,31]. While OC was expected to decrease with furosemide, owing to calcium loss and potential bone resorption, low concentrations made it difficult to ascertain effects of either furosemide, or turnout, or forced exercise. ...
... Interestingly, exercising slowly for up to 60 km per day had no influence on bone strength of two-year-old endurance horses . On the other hand, short sprints of 50 to 82 m per day, five days per week for six weeks was sufficient to increase bone breaking strength and bone mass in young calves (Hiney et al., 2004a) and bone optical density in weanling horses (Hiney et al., 2004b). Remarkably, the total distance exercised over the course of six weeks translates into only 1.5 km (Hiney et al., 2004a) and 2.5 km (Hiney et al., 2004b). ...
... On the other hand, short sprints of 50 to 82 m per day, five days per week for six weeks was sufficient to increase bone breaking strength and bone mass in young calves (Hiney et al., 2004a) and bone optical density in weanling horses (Hiney et al., 2004b). Remarkably, the total distance exercised over the course of six weeks translates into only 1.5 km (Hiney et al., 2004a) and 2.5 km (Hiney et al., 2004b). Hence, exercising up to 60 km per day slowly did not increase bone mass but sprinting between 1.5 and 2.5 km total over six weeks dramatically increased bone strength and mass. ...
Full-text available
In previous research, stall-housing growing horses resulted in decreased bone mineral content (BMC) of the third metacarpal (MCIII) compared to pasture-housing. To determine whether stall confinement negatively impacts bone, regardless of age, and whether the effects could be reversed upon return to pasture, 12 mature horses (5-15 years) and 12 yearlings were pair-matched by age and gender and randomly assigned to one of two treatment groups: pasture (PT) or stall (ST). Horses on PT remained there for the 84-d study, while horses on ST spent the first 28 d in stalls and the remaining 56 d on pasture. Radiographs and blood samples were taken on d 0 for baseline determinants. Radiographs and blood were taken every 7 d for radiographic photodensitometry estimates of BMC and analysis of osteocalcin (OC) and C-telopeptide (CTX-1)-markers of bone formation and degradation. There were no differences in BMC between treatments at the medial cortex of MCIII in mature horses. There were treatment (P=0.05) and day (P<0.01) differences in BMC at the lateral cortex of MCIII. In yearling horses, the BMC of the medial cortex of MCIII had a day difference with the lowest overall average at d 21 and highest at d 70 (P=0.04). There were day by treatment differences (P<0.05) for both OC and CTX-1 with the mature and yearling horses on ST having lower OC on d 14 than PT horses (P<0.05) indicative of reduced bone formation. In mature and yearling ST horses, CTX-1 was greater on d 14 and 28 compared to horses on PT (P≤0.05) suggesting greater bone resorption. Results from serum markers of bone formation and deformation confirm that stalling negatively impacts bone formation in horses regardless of age.
... Radiographic bone aluminum equivalents (RBAE) were validated for horses [2] as an estimation of BMC by comparing bone ash to radiographic density using an aluminum (Al) step wedge as a standard curve. Since that study, RBAE have been frequently used to detect changes in BMC, first with film radiographs [3][4][5] and, more recently, with digital radiographs [6] . ...
Digital radiographs are common for estimating bone mineral content (BMC) in horses with radiographic bone aluminum equivalents (RBAE). Processing algorithms are used to produce clearer images of digital radiographs in clinical settings, but this distorts RBAE. This study compared RBAE from digital radiographs to BMC from bone ash, and physical and digital morphology measurements. Digital radiographs were taken of six third metacarpals (MCIII) from equine cadavers with an aluminum stepwedge penetrometer. A 2-cm transverse section of bone was digitally analyzed and excised from each MCIII. For each image, a linear regression was created using the stepwedge thicknesses (R² > 0.99) and used to obtain total and individual RBAE. Outer and inner diameters of both dorsal-palmar (DP) and lateral-medial (LM) aspects, as well as cortical thicknesses were measured physically and digitally. Bone samples were ether-extracted, oven-dried, and ashed. Statistics were analyzed as correlations between variables. Physical and digital measurements of dorsal, medial, and lateral cortices, as well as DP outer diameter, tended to be similar (r > 0.74, P < 0.09) but palmar cortex measurements did not (r = 0.41, P = 0.42). The LM outer and DP/LM inner diameters were similar between the two methods (r > 0.95, P < 0.05). Total RBAE was strongly correlated to BMC (r > 0.93, P < 0.01). These results suggest that using digital radiographs to make morphological measurements is accurate and confirm the strong relationship between total RBAE and bone ash. However, this study emphasizes the need to use unprocessed radiographs for analysis.
... Evidence suggests that voluntary sprinting improves bone optical density and cartilage tissue in weanlings when compared to those housed in stalls (Bell et al., 2001;Billinghurst et al., 2003). While an effort was made to limit size of turnout to prevent the occasional sprint, a sprint of only 50 m, 5 d/wk may be sufficient to increase bone metabolism in young calves used as a model for horses (Hiney et al., 2004). The results observed across all treatment groups during phase I suggest that turnout and voluntary exercise may be sufficient to support joint health in young horses, similar to walking on a treadmill. ...
While beneficial in rehabilitation, aquatic exercise effects on cartilage and bone metabolism in young, healthy horses has not been well described. Therefore, thirty Quarter Horse yearlings (343 ± 28 kg; 496 ± 12 d of age) were stratified by age, body weight (BW), and sex and randomly assigned to one of three treatments for 140-d to evaluate effects of aquatic, dry, or no exercise on bone and cartilage metabolism in young horses transitioning to an advanced workload. Treatments included non-exercise control (CON; n=10), dry treadmill (DRY; n=10), or aquatic treadmill exercise (H2O; n=10; water: 60% wither height, WH). Horses were housed individually (3.6×3.6 m) from 0600 to 1800, allowed turnout (74×70 m) from 1800 to 0600, and fed to meet or exceed requirements. During Phase I (d 0-112), DRY and H2O walked on treadmills 30 min/d, 5 d/wk. Phase II (d 113-140) transitioned to an advanced workload 5 d/wk. Every 14-d, WH, hip height (HH), and BW were recorded. Left third metacarpal radiographs on d 0, 112, and 140 were analyzed for radiographic bone aluminum equivalence (RBAE). Every 28-d, serum samples were analyzed for osteocalcin and C-telopeptide crosslaps of type I collagen (CTX-1), and synovial fluid samples were analyzed for prostaglandin E2 (PGE2), collagenase cleavage neopeptide (C2C), collagenase of type I and type II collagen (C1,2C), and carboxypeptide of type II collagen (CPII) using ELISAs. All data were analyzed using PROC MIXED of SAS, including random effect of horse within treatment, and repeated effect of day. Baseline treatment differences were accounted for using a covariate. There were treatment × day interactions (P<0.01) where OC and CTX-1 remained consistent in both exercise groups while inconsistently increasing in CON. There were no treatment differences (P>0.30) in RBAE, BW, or HH, but all increased over time (P<0.01). There were no treatment × day interactions of synovial inflammation or markers of cartilage metabolism, however there was an effect of day for each marker (P<0.03). Changes in biomarkers of cartilage turnover in horses exercised at the walk, whether dry or aquatic, could not be distinguished from horses with access to turnout alone. This study indicates that early forced exercise supports consistent bone metabolism necessary for uniform growth and bone development, and that there are no negative effects of buoyancy on cartilage metabolism in yearlings transitioned from aquatic exercise to a 28-d advanced workload.
... Similar to earlier in vitro bone studies discussed earlier, these studies reduced confounding by restriction or matching to gender, breed and age (Boyde and Firth 2005, Davies 2005, Davies 2006, Anthenill, Gardner et al. 2010. It is therefore not unreasonable to assume that the increased exposure to exercise would be directly proportional to increased bone modelling, in particular towards the region of highest strain (McCarthy and Jeffcott 1992, Carstanjen, Lepage et al. 2003, Hiney, Nielsen et al. 2004, Firth, Rogers et al. 2005b). However, the strain stimulus is reduced as bone mass increases and improves fatigue life. ...
Short sprints performed during growth can increase bone strength, mineral density, and cortical widths, but their impact on joint health is not fully understood. Some studies have found joints of young animals are damaged by forced sprints, while others found confinement hindered joint development. This study aimed to determine the impact of short sprints on synovial fluid neopeptide collagenase cleavage of type I and II collagen (C1,2C) and cartilage glycosaminoglycan (GAG) content. Calves were used as a model for young horses in this terminal study. Twenty-four Holstein bull calves were assigned to treatment groups of 1, 3, 5, or 0 days/week of sprinting (n=6). A sprint consisted of an individual calf being walked from its stall and down a 71-m concrete aisle, at the end of which the calf was released, and encouraged to sprint towards the barn. Calves remained on treatment for 6 weeks and were euthanized on day 42. Immediately post-euthanasia synovial fluid was sampled from the middle carpal joint and cartilage discs sampled from 9 locations on the carpal bones. Analysis was performed in SAS 9.4 with fixed effects of treatment and bone. There were no differences in C1,2C or GAG concentrations between treatments (P = 0.73 and P = 0.96, respectively), but there was a difference between individual carpal bone GAG concentration (P = 0.03). Short sprints for 6 weeks during growth did not impact middle carpal joint C1,2C or carpal bone GAG content, and should be permitted given the benefits to bone health.
One of the main goals of horse breeding industry is to raise animals with a sound and adequate musculoskeletal system that withstands the rigors of training and competition. Therefore, the knowledge of the most adequate growth model for each breed and purpose, as well as the factors that influence skeleton development, is of high concern for breeders and users. The Lusitano horse is no exception. This Portuguese breed has become more popular as a sport and leisure horse due to its functional and behavior characteristics. In this review we will bring about an integrated approach on the characterization of the Lusitano production systems, both for the broodmare productive cycle and further foals’ growth and development. In particular, the application of non-linear models to foals’ growth data from birth to the onset of training, has enabled a comprehensive overview on growth patterns of the Lusitano horse when managed in extensive systems, which constitutes innovative information for this breed. Based on the achievements of our research team, the relationship among growth patterns, bone metabolism and osteoarticular quality are also highlighted.
Full-text available
Previous research has determined that maintaining young animals in stalls is detrimental to their bone health, while the addition of 50 to 82-m sprints 5 d/wk aids in counteracting the reduction of bone strength from confinement. The current research aims to determine if 1 or 3 d/wk of sprinting affords the same benefits to bone as 5 d/wk of sprinting compared to animals confined with no sprinting. Twenty-four Holstein bull calves were obtained from the Michigan State University Dairy Cattle Teaching and Research Center. At 9 weeks of age, calves were randomly assigned to treatments of 1, 3, or 5 d/wk of sprint exercise, or to the confined control group sprinted 0 d/wk. Each treatment had 6 calves. Individual sprinting bouts included a single sprint down a 71-m concrete aisle. For the duration of the 6-wk study, calves were housed at the MSU Beef Cattle Teaching and Research Center in stalls which afforded calves room to stand, lay down, and turn around. Serum was collected weekly via jugular venipuncture to obtain concentrations of osteocalcin (OC) and C-telopeptide crosslaps of type I collagen (CTX-1) - markers of bone formation and degradation respectively. Sprints were videotaped weekly to determine stride frequency and sprint velocity. On d 42, calves were humanely euthanized at the Michigan State University Meat Lab and both front limbs were immediately harvested. Computed tomography scans and mechanical testing were performed on the left fused third and fourth metacarpal bones. Serum OC concentration was greatest for calves sprinted 5 d/wk (P < 0.001). Calves sprinted 5 d/wk had both greater stride frequency (P < 0.05) and lower sprint velocity (P < 0.05). All exercise treatments experienced greater dorsal cortical widths compared to control animals (P < 0.01). Through mechanical testing, fracture forces of all sprinting treatments were determined to be greater than the control treatment (P < 0.02). Results from this study support that sprinting 1, 3, or 5 d/wk during growth can increase bone health and cause favorable alterations in bone markers. While all exercise treatments had over a 20% increase to fracture force, calves sprinted 1 d/wk sprinted only 426 m over the 6-wk study and still experienced over a 20% increase in bone strength compared to confined calves. This study demonstrates the remarkably few strides at speed needed to enhance bone strength and emphasizes the danger to skeletal strength if sprinting opportunities are not afforded.
Full-text available
Regulation of the magnitude and distribution of skeletal strain is achieved in limb bones both “internally” by alterations to bone morphology, and “externally” by coordination of muscle activity and modifications in the animal's behavior. Though not actually minimizing functional strain, these mechanisms conspire to produce a restricted strain environment, which allows an economical and optimized structure, and, in a variety of species over a wide range of activities, the architectural and behavioral modifications have resulted in remarkably similar peak functional strain magnitudes. This confined range of functional strains reflects a universal mechanism and objective of structural adaptation in bone.
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Three triple-element rosette strain gages were attached to the equine third metacarpal midshaft to record site-specific strains engendered by locomotion. The distribution of strains acting upon the midshaft cross section were characterized using a combined beam theory and finite element model analysis that did not presume the manner by which the bone was inertially loaded. A medium-speed trot (3.6 ms-1) was chosen as a representative speed and gait, with normal and shear strains, and strain energy density (SED) distributions determined throughout the stance and subsequent swing phase. Importantly, the sites of maximum compression (-2400 mu epsilon), tension (810 mu epsilon), shear (1500 mu epsilon), and SED (54 kPa) were not located at any of the gage attachment sites, emphasizing that a minimum of three rosette gages are necessary to resolve the peaks and locations of functionally induced normal and shear strains. Considering the nonuniform strain distributions across the cortex, we conclude that the third metacarpal is subject to a complex loading milieu comprised of bending, axial compression, end shear, and torsion. As this complex manner of loading was consistent through the entire stance phase, it would appear that, at least during the trot, specific sites within the same cross section are subject to vastly different magnitudes of strain stimulus.
In this study, effects of exogenous somatotropin (eST) on cortical bone width were evaluated in a group of juvenile horses in race training. Radiographs of the third metacarpal from 31 juvenile race horses were obtained from a previous study (19). The horses had been paired by age and sex and randomly assigned to treatment with daily injections of eST (n = 16) or saline (n = 15). Radiographs were measured for total bone diameter and cortical bone width at three sites using a digital micrometer. Average total bone diameter in the dorsal-palmar plane on d 0 was 30.701 mm at Site A, 31.331 mm at Site B, and 31.071 mm at Site C. There was no significant change in bone diameter on d 64 of the treatment period. By d 128, there was an increase (P < 0.05) in bone diameter in the dorsal-palmar plane at all three sites and in the lateral-medial plane at Sites B and C. The eST-treated horses had a significantly greater increase in dorsal-palmar bone diameter at all three sites on d 128 than the control horses (P < 0.05), but treatment did not affect lateral-medial bone diameter. There was a decrease (P < 0.0001) in medullary cavity width in the dorsal-palmar plane but no change in the lateral-medial direction. At d 64, there was a greater decrease in medullary cavity width (dorsal-palmar) at Site B (P < 0.02) in the eST-treated group than in the control group. By d 128, the eST-treated horses had a greater decrease in medullary cavity width (dorsal-palmar) at both Site B (P < 0.01) and Site C (P < 0.02) than the control horses. By d 128, eST-treated horses had a greater increase (P < 0.01) in dorsal cortical bone width of the third metacarpal than the control horses, but treatment did not significantly affect medial, lateral, or palmar cortical bone width.
Motivation is the concept used to describe how behavior is both initiated and directed toward a goal. Motivation affects the welfare of enclosed livestock through all the physiological and psychological pathways that relate behavior and welfare, particularly those involved in the body's maintenance of homeostasis and its response to acute and chronic stressors. Increased motivation for locomotion and kinesis in response to chronic deprivation of movement is one of the most readily demonstrable effects of chronic close confinement of livestock. Chronically unsatisfied motivation may be manifested as stereotypies; in livestock species these most often involve movements of the mouth or limbs. The major aspects of livestock housing that affect the welfare of enclosed livestock are the quality, amount and type of space, amount and duration of movement restraint, and sensory deprivation imposed on the animals. Systematic research into the behavioral and physiological effects of these factors, and their variation within and across different species, breeds, sexes and ages of livestock is required if current ethical issues regarding the welfare of enclosed livestock are to be resolved objectively and efficaciously. While the resolution of ethical controversies regarding the welfare of enclosed livestock is ultimately philosophical and the responsibility of human society at large, it is the challenge of applied ethologists and other scientists in related fields to improve our knowledge of significant relationships among motivation, behavior and welfare. The further elucidation of the many and complex factors that influence motivation and the formulation of objective criteria of animal wellbeing that include a reasonable consideration of the animals' probable emotional or subjective experience must also be researched.
Fifty-three Quarter Horses were put into race-training at 18 mo of age. Changes in the third metacarpal were monitored by radiographic densitometry initially at 83 days prior to the commencement of training and at days 0, 62, 104 and 244 of training. A normal increase in density of the third metacarpal due to growth and mineralization was seen from the first set of radiographs until the horses began training at day 0 (P<.001). Bone density then decreased to day 62 (P<.001), remained low through day 104 before it began to increase to day 244 (P<.005). Differences in the most optically dense portion of each cortex of the third metacarpal were compared in horses completing the study without injury and those sustaining a bone-related injury. Horses experienced fewer injuries when they had greater cortical mass in the lateral (P<.05) and medial (P<.1) aspects of the third metacarpal, relative to the palmar aspect, at the commencement of training.
Thesis (M.S.)--Texas A&M University, 1998. Includes bibliographical references (leaves 106-115). Vita. "Major subject: Animal Science".
Mature bone can adapt to strenuous exercise, but no study has correlated the changes in bone in vivo strains, remodelling and mechanical properties that occur as a consequence of strenuous training. Therefore, we examined exercise-related remodelling and in vivo strains in the tarsometatarsus (TMT) of three groups of adult (post-physial closure) White Leghorn roosters: basal control (30 weeks of age), age-matched control (39 weeks) and exercise (39 weeks). Exercise birds ran for 1 h a day, 5 days a week for 9 weeks at 70-75% of predicted maximum aerobic capacity. During treadmill locomotion, in vivo strains were recorded from miniature rosette strain gauges implanted on anterior, medial and lateral TMT cortices. TMT mechanical properties were measured with three-point bending tests to failure. Cortical morphometry was digitized from photographic slides of a 1-mm thick mid-diaphysial cross section of each bone. Exercise and age-matched control TMTs had significantly greater cortical area and maximum load than had basal controls. Exercise axial strains significantly exceeded basal and age-matched control strains along the anterior and lateral surfaces. Age-matched control anterior axial strain was twice that of the basal control. The mature bone remodelling suggested that the structural properties optimized by exercise-induced remodelling may differ from those optimized by age-related remodelling. The findings support the osteoregulatory role of strain but contradict earlier data suggesting that strain magnitudes do not change significantly with age or exercise.
The effects of exercise and relative inactivity on cortical bone were compared in young horses. Two groups were used; one was given a 14-week programme of exercise (n = 6) and the other kept as unexercised controls (n = 6). The first nine weeks of exercise involved trotting and cantering (2 to 4 km d-1 at speeds up to 12 m s-1) on a treadmill set at an incline of 3 degrees. Over the next five weeks the horses were trained at near maximal speeds (that is, up to 14.5 m s-1) with no incline of the treadmill. At the end of the programme marked differences in cortical porosity and distribution of subperiosteal osteogenesis at the mid-shaft of the third metacarpal bone were found between the groups. Histomorphometrical examination of the dorsal cortex showed minimal bone remodelling in the exercised horses, but extensive modelling as evidenced by the large amount of subperiosteal bone formation. In contrast, the unexercised horses had significantly more bone remodelling and less formation of subperiosteal bone. The histomorphometric and microradiographic findings provided an explanation for changes in the non-invasive bone measurements that occurred during training. Bone mineral content of the mid-metacarpus was found to increase more in the exercised than the unexercised horses despite a lower overall growth in bodyweight. In those horses that completed the full training programme, ultrasound speed increased significantly by the end of the training programme. It remained unchanged in the horse that did not complete the full exercise programme and decreased slightly in the unexercised horses. The difference in ultrasound speed between the groups was considered to reflect differences in intracortical bone porosity, endosteal bone formation and alterations in skin thickness. The stiffness of cortical bone increased significantly in the exercised horses but remained unaltered in the unexercised horses.
Nineteen weanling horses (average age = 147 d) were divided into exercised (EX; n = 10) and nonexercised (NEX; n = 9) groups, with age, sex and breed represented as equally as possible. The EX group was exercised on an automatic walker at a medium trot for up to 20 min, 5 d each week. Both groups were fed to meet 100% of their protein and 110% of their energy requirements (NRC, 1978). The EX group's diet was supplemented, on exercise days, with corn starch to meet the additional energy requirements for exercise. The experiment was conducted over a 111-d period. Body weight was measured at 10-d intervals, and height at the withers and metacarpal circumference was measured at 20-d intervals. Radiographs of the distal radius, metacarpal joint and the proximal and distal ends of the third metacarpal were taken at 147, 218 and 255 d of age to determine bone density and to observe any possible bone abnormalities. There were no differences between groups in weight or wither height gain; however, gain in third metacarpal circumference was greater (P less than .01) in the EX group than in the NEX group from 167 to 215 d of age. Bone density in the EX group increased by a greater amount (P less than .06) than in the NEX group by the end of the trial. There were no lameness problems or bone abnormalities observed in either group. Exercise training of horses during the weanling to yearling age period was shown to improve the stress-bearing characteristics (radiographic bone density and metacarpal circumference) of the third metacarpal without affecting the quantity of body growth.