Cardiovascular Response To Exercise In Iranian Athletic Horses
M Sakha, A Rezakhani, H Rahmani
cardiac response, exercise, heart, hematocrit, horse
M Sakha, A Rezakhani, H Rahmani. Cardiovascular Response To Exercise In Iranian Athletic Horses. The Internet Journal of Veterinary Medicine. 2007 Volume 5 Number 1.
Various body systems or organs are responsible for successful performance in
horses. The cardiovascular system has great role in the evaluation of exercise
tolerance in horses. In this study ,cardiovascular response of 19 Iranian race-
horses, before and after exercise in 1600 meter race-track were studied . Heart
rate before and after exercise and pattern of its reduction after exercise and
correlation between these data and poor performance were evaluated. The mean
of resting heart rate was 36.10+_5.54 bpm. The mean of maximum heart rate and
heart rate after sixty minutes of exercise or HR(60), were 131.89+_16.83 and
42.36+_11.70 bpm respectively. The maximum heart rate showed significant
increase to resting heart rate(p<0.05).The mean decrease of heart rate in first
minute was 15.38 percent. Eleven horses (60 %) had HR of 60 bpm after twenty
minutes.21.1 percent of horses had normal HR after thirty minutes. The mean
values of PCV (paced cell volume) and RBC (red blood cell) were 36.60± 3.3 %
and 6.8± 0.88 M/ul at rest and 44.73± 4.7 % and 9.28± 1.32M/ul after exercise
respectively. These values showed significant increase after exercise (p<0.05).
Exercise intolerance is a suboptimum capacity to perform at the expected or
previously attained intensity of exercise. The expectations of the owner or trainer
are inherent in the definition of exercise intolerance, thus factors other than
diseases must be considered.
Exercise intolerance and poor performance are signs that may be referable to
diseases in many body systems. However the respiratory, cardiovascular and
locomotor systems are of primary interest. They play a central role in the
integrated response of the body to the increased demand of muscle for oxygen
and energy substrates during exercise.
The cardiovascular system plays a central role in the oxygenation of blood by
the lungs and in the delivery of oxygen and other energy substrates to, and
removal of metabolic products from exercising muscles.
.Physical examination of the heart for detection of heart rate at rest and post-
exercise, vagal effect on heart rate after exercise, taking the pulse , presence of
dysrhythmias, PCV and RBC volumes are used to evaluation of cardiovascular
Materials and Methods
19 Iranian cross-bred race horses aged between 5 to 10 years old and 350 to 450
Kg weight were selected for this study. Two blood samples were taken at rest
and after exercise in 1600 meter race- track. Auscultation of heart for heart rate
and possible dysrhythmias carried out at rest and immediately after exercise, every
minute up to 15 minutes, and then every 5 minutes up to 60 minutes. Blood
samples submitted to the laboratory for hematological analysis and heart rate data
analyzed for decreasing rate in certain periods. The statistical analysis carried out
by t-student test and anova test with SPSS computer program.
Table 1 show the mean of resting heart rate(HR),maximum HR and heart rate
after sixty minutes of exercise HR(60).There is significant increase of HR after
exercise (p<0.05).The mean percentage decrease of HR in first, second and fifth
minutes after exercise are shown in table 2.Table 3 shows the hematocrit and red
blood cell values before and after exercise. The values showed significant increase
after exercise (p<0.05).
Among the adaptive cardiovascular responses to training are lowered heart
rate,which is necessary to achieve a set speed, increased red cell volume, and
increased capillarisation of muscle.
Increase in heart rate is primarily responsible for increasing cardiac output during
exercise at submaximal heart rates (<210 bpm).At maximum heart rates (210 to
240 bpm)subsequent increments in cardiac output were thought to result from
increased stroke volume as in humans, but this is now not thought to be the case in
The rate of decrease of heart rate following exercise and the time required to reach
resting levels depends upon the severity of the exercise even in fit horses. Heart
rate falls rapidly over the first minute and then more slowly over the ensuing 10 to
15 minutes period.
In this study the mean of resting heart rate was 36.10±5.54 bpm. The mean of
maximum HR and the HR of sixty minutes after exercise were 131.89±16.83
bpm and 42.36±11.70 bpm respectively, showing significant increase of resting
heart rate (p<0.05).
The mean decrease of heart rate in first minute was 15.38 percent indicating good
cardiovascular response in some of the horses.
The mean of resting HR of this study is similar to studies of Steel (35.9±5.81
bpm) and Lank et al (42.6bpm) on warm blood horses.
The maximum HR between horses do not show any significant differences
(p>0.05) and the mean of maximum HR (131.89±16.83 bpm) indicates
submaximal exercise in these horses. Manohar (1993) reported maximum HR of
213 bpm in race horses. Hiragan et al (1997) reported maximum HR of
229.3±11.4 before initiation of training program in thoroughbred horses.
Boden (1991) reported maximum HR of 250 bpm in young horses and showed
that after a standard training program, there is a decreasing rate in HR at rest and
also maximum HR.
The mean of maximum HR in standard bred horses was reported 227±2.4 bpm
and 228±3 bpm in thorough bred horses(Mooris1991).
In this study the mean of decreasing HR in first minute was 15.37 percent, with
range of 5.77 to 30 percent. Nearly 42 percent of horses showed decreases of more
than the mean. The mean decrease in the second and fifth minutes were 29.18 and
50.62 percent respectively.
Eleven horses (60 %) had HR of 60 bpm after twenty minutes.21.1 percent of
horses had normal HR after thirty minutes and it reached to mean of 36.8 after
forty minutes. Only 63.2 percent of horses recovered to normal resting heart rates
after sixty minutes. The mean of HR after sixty minutes was 42.36±11.72 bpm.
In the study of Physick-sheard (1985) on thoroughbred race horses with
mean velocity of 886±49 m/min ,the mean of returning to resting HR, was 45±7
bpm at sixtieth minutes and was not followed after it.
Although the rate of decreasing of HR is much valuable in endurance horses, but in
race Horses, the decrease rate of HR in few first minutes after exercise is very
significant and decreasing rate of fifty percent or more, suggestive of possible good
performance. If HR does not return to normal after sixty minutes, there is possibly
an evidence of poor performance in the horse.
Hodgson and Rose (1994) suggested that recovery of HR to 60±4 bpm in ten
minutes after high speed exercise is a good benchmark for high compatibility of
the heart to exercise. Radostits et al (2000) suggested that horses which have not
HR of 60 bpm or were twenty minutes after exercise, are not suitable for
Taylor and Hillyer (1997) suggested a general guide that HR should reach to
more than 10% of normal HR after 15 minutes at canter and after 30 minutes in
gallop. Eleven horses (60 %)of this study had HR of 60 bpm after twenty
minutes.21.1 percent of horses had normal HR after thirty minutes. Only 63.2
percent of horses recovered to normal resting heart rates after sixty minutes.
In this study fourteen horses have a good slope of decrease for HR.Five horses
have not a good performan cefor example, two of them did not reach normal HR
even after 60 minutes. Six horses (31.57%) have HR more than 10% greater than
The mean of decreasing HR in first five minutes was 50.62% and 57.8% of
horses had recovery rate more than the mean. Whenever nearly 60 % of horses
have decreasing rate ,more than the mean decrease, possibly there is a evidence
for good performance.
The spleen of horses is densely innervated and normally can deposit up to one
third of total red blood cell in the blood. After exercise or hemorrhage, the spleen
can release this deposition and therefore hematocrit(PCV) value can show up to
a fifty percent increase( Hodgson 1994).
The RBC and PCV mean values of this study showed significant increase after
exercise(p<0.05).The mean increasing percentage for RBC was more than 30%
and for PCV was more than 20%.Meetay et.al (1992) showed 58-61 % increase
in RBC and PCV values after competitive racing in thoroughbreds. Hirage et.al
(1997) revealed significant difference of PCV values after a training period. In a
study by Gill et.al (1987) on 3-day events and show jumps, there was a
significant increase in PCV and RBC values.Person and Alberg (1979)
suggested that a low stimulus can produce 10 to 15 percent increase in RBC
values.They suggested individual susceptibility among horses that will become
higher as increasing of age.
In a study on splenectomized horses, there was no increase of PCV values after
physical stress or injection of epinephrine( Person et.al 1973). Radostits and
Blood (2000) suggested that an increase of 26 % in RBC values reveal good
capacity of the spleen.
The increase of whole blood volume during the exercise, is dependent on
intensity of exercise, age, sex, breed and type of training. Up to 200% difference in
the weight of spleen in various breeds may cause differences in whole blood
The maximum HR of the horse,the speed of timely reduction, RBC and
spleen reservation to increase the PCV value are good indicators for cardiovascular
assessment of poor performance evaluation. The mean decrease of heart rate
in first minute indicates good cardiovascular response in some of the horses.12
horses (63.15%) had a normal heart rate at sixty minutes after exercise, possibly
due to irregular training and the rest did not return to their resting heart rate
after 60 minutes. Fourteen horses of this study have a good slope of decreasing
HR. The rest did not show a good decreasing rate curve. The mean of decreasing
HR in first five minutes was suitable and nearly 60 % of horses have decreasing
rate of more than the mean, possibly a evidence for good performance. Those
horses with more than 30% increase in PCV have good spleen potential for RBC
This project is funded by faculty of veterinary medicine, kerman university and the
author wishes to thanks from the laboratory of faculty for hematology works of
Faculty of specialized veterinary sciences, Science and research branch, Islamic Azad university, Ponak sq., Tehran, Iran ,Tel:+98 21 4804171 Fax: +98 21 4804170 firstname.lastname@example.org