Cardiovascular and Respiratory Function in Horses:
Their Role in Determining Racing Performance
and How Training Affects Them
James H. Jones
Department of Surgical and Radiological Sciences
Giannini Equine Athletic Performance Laboratory
School of Veterinary Medicine
University of California, Davis USA
[email protected]
Topics
• Comparative exercise physiology
• Energy use during exercise – muscles
• Sources of energy during exercise
• Importance of oxygen for supplying energy in racing
• Roles of heart and lungs in delivering oxygen to
muscles
• How training affects heart and lungs
• Related issues – bleeding, shipping fever
• Questions
Comparative Exercise Physiology
Study different animals when they exercise in
order to better understand factors that affect
and limit the exercise capacity and racing
ability of the horse
Giannini Equine Athletic Performance Lab
Exercise measurements in lab with controlled conditions
Japanese Ban-ei (輓曳)
Hokkaido Draft horse races – 1000 lb sled with hills
Jockey only uses reins, no whip - 200 yd in 4 minutes
Maximum running speeds of mammals
(J.H. Jones and S.L. Lindstedt (1993) Ann. Rev. Physiol. 55)
Cheetah
Blackbuck
Fastest mammals
are 65-110 lb
Pronghorn
Horse
Dog
Human
Etruscan
Shrew
Elephant
Limb Excursions during Running and Body Size
¼ oz Pygmy Mouse
12,000 lb African Elephant
Galileo Galilei (1637)
Discorsi e dimostrazioni matematiche,
intorno à due nuove scienze
In the Barbaro
US, 1 in –1500
flat racing
starts
results in a
Preakness
Stakes
2006
Barbaro injury
catastrophic musculoskeletal
2006 Kentucky Derby
110 lb Pronghorn Antelope Cannon Bone
Pronghorn Antelope and Cheetah
Fastest Mammals – 100 lb
Pronghorn Antelope Fawn
What physiologically determines a
horse’s racing performance?
The horse that applies the greatest amount
of mechanical power to the ground in a
coordinated manner will propel itself the
fastest around the track
What physiologically determines a
horse’s racing performance?
• Coordination is determined by conformation and
the development of nervous system control of
movement and stride = efficient gait
• Mechanical power is determined by the amount
of force developed by the muscles and their
speed of shortening – and how long peak power
can be maintained – this is affected by training
British Triple Crown races winning times, decade averages, 1845-1999
J.H. Jones (1998) Principles of Animal Design, E.R. Weibel et al. (eds.)
WINNING TIME (s)
200
190
ST. LEGER (2937 m)
180
170
OAKS (2423 m &)
160
DERBY (2423 m %)
1860
1880
1900
1920
YEAR
1940
1960
1980
2000
American Triple Crown races annual winning times, 1925/26-1999
J.H. Jones (1998) Principles of Animal Design, E.R. Weibel et al. (eds.)
WINNING TIME (s)
150
BELMONT STAKES (2414 m) 1926-
140
130
KENTUCY DERBY (2012 m) 1926-
120
110
PREAKNESS STAKES (1911 m) 19251930
1940
1950
1960
YEAR
1970
1980
1990
2000
What is the majority of energy used to do
during locomotion, i.e., what is the
major energy cost of locomotion?
Most of the
energy used during
locomotion is used
to support the
animal’s body
weight vs. gravity!
Why does it cost more energy to
move faster than slower?
Whether an animal moves quickly or
slowly, most of the energy used by its
muscles is simply being used to support
its body weight against gravity –
but the amount of force and rate
of its application change with speed
Force-integrated Treadmill
Dr. M. Weishaupt – Univ. Zurich
Increased Muscle Force
for Higher Speed
• Force is generated when actin
and myosin proteins in muscles
form temporary cross-bridges
• Each cross-bridge requires the
energy contained in a chemical
called ATP to generate force
• More force requires use of a
greater amount of muscle that
is faster and uses more ATP to
generate the same amount of
force over time
Breakdown of ATP to ADP releases
energy to muscle
ADP requires energy from muscle
metabolism (aerobic or anaerobic)
to restore ATP
Duration of Peak Metabolic Power
For muscle to continue to generate force for
more than a few seconds, ATP must be
replenished by adding a ~P to ADP from
creatine phosphate (CP), anaerobic glycolysis
or aerobic (using oxygen) ATP resynthesis
Highest total metabolic power occurs for the
shortest possible duration – single
contraction
Sprint races occur with significant ATP from
anaerobic glycolysis and ↑ Lactic Acid (LA)
Longer duration exercise can only be
sustained with aerobic = slower speed
Sprint at end increases anaerobic glycolysis
above aerobic limit (VO2max) = ↑ Lactic Acid
1
45000
30000
15000
10
20
30
s
40
50
World Record Running Speeds
↑ Speed Requires ↑ Total Metabolic Power
Strength
Endurance
Skeletal Muscle Plasticity
Strength-trained fibers:
• large diameter
• low capillary:fiber ratio
• uses little oxygen
• fast shorten, 
Endurance-trained fibers:
• small diameter
• hi capillary:fiber ratio
• uses much oxygen
• slow shorten, 
↑ Speed Requires ↑ Total Metabolic Power
Leveling out of aerobic power
= no further ↑ w/speed
= VO2max
Training Effects on Aerobic Capacity and Lactic Acid
After training
•
VO2max
Margaria et al. 1963
The Respiratory System
It’s bigger than you think!
Lungs – bring oxygen into
breaths volume volume
the body, remove carbon
minute
breath
minute
dioxide – an acid!
beats volume
minute beat
volume
minute
Maximal Heart Rates of Mammals (Allometric)
R.V. Baudinette (1978)
J. Comp. Physiol. 127
Weibel, E.R. et al. (2005)
J. Exp. Biol. 208
Training Effects on Heart Rate and Lactate
Heart is a muscle and gets stronger and larger with
use (training) – volume of blood with each stroke ↑,
so more blood flow with ↓ heart rate
Hematocrit and blood viscosity changes in
exercising Thoroughbreds (shear rate 450/s)
Apparent Viscosity (cP)
M.R. Fedde and H.H. Erickson (1998) Eq. Vet. J. 30
Packed Cell Volume (%)
5%
50%
100%
.
Percent VO2max
Visceral Piston Linking Stride and Breathing
D.M. Bramble and D.R. Carrier (1983) Science 219: 251-256
Body position
Footfall
Ventilation
Thoracic loading
Support
Mammalian lung volume vs. Body mass
Horse (1,100 lb)
Goat
(110 lb)
Fox (11 lb)
33 ft
Pilot
whale
Breathing entrainment with stride during gallop
Heart Rate
Respiratory Rate
and Volume
Stride frequency
at gallop
±132 / min
= 2.2 / sec
= 0.4 s / breath
= 0.2 s / in or out
Left Laryngeal Hemiplegia – “Roarer”
Goals of training
• Training has three major physiological goals
– develop the musculoskeletal system to be able to withstand
the peak loads and stresses that will occur with high-speed
running
– develop the muscles to be able to generate high amounts of
metabolic power
– develop the cardiovascular and respiratory systems to be
able to supply large amounts of oxygen to the muscles so
they can sustain high metabolic power burning oxygen and
not build up lactic acid
• Other goals: mental/psychological, coordination, etc.
Load into air stall, wait & load onto aircraft
Heat
Ventilation
Waiting ….
Loading onto airplane
EIPH – “Bleeding”
Palv
Ppl
P = Ptm
P·r
=
t
Pcap
Horses do not have a thin or
weak barrier between blood
air in lungs – thicker and
stronger than most mammals!
Pronghorn antelope (PH) vs. Thoroughbred (TB)
-1
or Specific Cardiac Output (Q, ml s
.
.
2
2
12
150
4
3
100
2
50
1
0
.
VO2/Mb
.
Q/Mb
0
Paorta
Ppulm art
Mean Blood Pressure (torr)
Specific O2 Consumption (VO2/Mb, ml s
-1
kg-1)
-1
kg )
Pronghorn
antelope has higher VO2max/kg and250
20
Rest
1 SE is P
Q/kg18but PaoTB
and
P
are
much
lower.
Why
PH Rest
PA
PA
.
16
TB VO max
200
so high
in
the
.exercising horse?
14
PH VO max
Positions of sonomicrometer crystals on
Thoroughbred horse left ventricles
Aorta
Aorta
PA
RA
PA
LA
1
2
RV
3
44
LV
55
LV
66
77
88
LV pressure generation and relaxation during exercise
Standardized Change in Variable from Rest
Left ventricular
relaxation rate does not increase
7
with exercise as much as LV rate of
pressure
dP/dt
6
generation
– could cause increased diastolic
abs(-dP/dt)
pressure = increased PLA
5
th = 1/HR
4
1/tc
3
PLVmax
2
1
0
2
4
6
8
Speed (m/s)
10
12
14
Origin of EIPH - pulmonary or bronchial?
Mean systemic arterial pressure at rest and VO2max
Various sources - J. Appl. Physiol. and Am. J. Physiol.
150
.
VO2max
m = 7.86
Rest
*
100
0
0.01
0.1
1
10
Body Mass (kg)
100
Steer
Horse
Calf
Pony
Mini Pig
Dog
Goat
Rabbit
Rat
50
m = 1.36
Mouse
Mean Arterial Pressure (mm Hg)
Despite
250 tendency for larger mammals to have
higher arterial pressures at VO2max, horses are
200
exceptionally
high – why?
1000
“Many horses, especially young horses,
are oft subject to this bleeding at the nose
. . . it proceedeth from much abundance of blood or
the vein which endeth in the head is either broken,
fretted or opened.”
Gervase Markham (1610 (1st ed., 1656 8th ed.)) Markham’s
Maister-Peece: Containing All knowledge belonging to
Smith, Farrier, or Horse-Leach, touching the curing of
all diseases in Horses
Gervase Markham (1610 (1st ed., 1656 8th ed.))
Markham’s Maister-Peece: Containing all knowledge belonging to Smith, Farrier,
or Horse-Leach, touching the curing of all diseases in Horses
"...no work...has done more damage to veterinary progress.“
(J.F. Smithcors and A. Smithcors (1997))
Fiberoptic Endoscopy
EIPH blood in airways originates in lungs
EIPH lesions – caudodorsal lungs
Exercise-Induced Pulmonary Hemorrhage
• J.R. Pascoe et al. (1981) Am. J. Vet. Res.
44% bronchoscopy; EIPH, “bleeding”
• C.R. Sweeney (1991) Vet. Clin. North Am. Equine
TB: 44-95%; App: 52%; SB: 26%
• K.E. Whitwell and T.R.C. Greet (1984) Equine Vet. J.
Tracheal wash - hemosiderophages - 100%
Blood pressures in horses are much higher
than in most mammals
Transport Time and Risk of Shipping Fever
3 3year-old
JRA Thoroughbreds prior to registration as racehorses (N = 37)
year-old JRA Thoroughbreds prior to registration as racehorses (N = 37)
Cumulative Percentage of Pyrexic Horses (%)
(Oikawa
Jones,
AHSA
Guidelines, 2000)
(Oikawa
andand
Jones,
FEI
Recommendations,
1999)
50
40
30
20
10
0
0
5
10
15
20
25
30
35
Number of Hours Elapsed During Transport (h)
40
Transport Time and Risk of Shipping Fever
JRA
with pyrexia
pyrexia (T
(Tb >>38.5°
38.5°C)
C)postpost-ororduring+post-transit
during+post-transit
JRA horses
horses with
b
Percent of Horses Pyrexic Post-Transport (%)
(Oikawa
and Jones,
Guidelines, 2000)
(Oikawa
and Jones,
FEI AHSA
Recommendations,
1999)
50
1993-1994
N = 37
45
40
35
30
25
20
1989-1994
15
N = 4,236
10
5
1993-1997
N = 163,264
0
< 1000 km
(< 24 h)
1000-1300 km
(25-28 h)
1708-1858 km
(36-41 h)
Distance (and Time) Horses Transported
Heart RateVariability in Stall and Road Transport
Stall Rest
Road Transport
2000
1600
1200
s2
)
800
0
400
52
48
44
Hear
36
t Rat
32
e (be
at mi -1
n )
40
200
Po
56
we
r
600
(m
800
400
HF
2
)
s
LF Power (m
2400
Nihon Tei-en in Davis, California