sand is firm closer to the waves. The impact of transporting the horses was an
interesting factor and again not unexpected. It has been shown that horses
dehydrate when transported and are more stressed (Stull et al and Yanez-Pizana et
al) and both these factors are going to result in an increase in the core temperature
of exercising horses.
The decreased prevalence of PRDS when horses race at night was the same as in
the previous paper when looking at the races at the Newmarket racecourse. This can
be attributed to the cooler temperatures experienced at night. However, in November
2009 the lights were moved to the Turffontein race course. At this course, there was
no decrease in the prevalence when racing after 18h00, but this can be attributed to
the smaller numbers of runners so far, as well as one particular horse that shows
PRDS virtually every time he races. As time goes on and the numbers increase, it is
expected that the prevalence of PRDS at night at this track will decrease.
It was interesting to note that the fitting of blinkers is now shown to be not significant.
This is in contradiction to the previous paper, but the increased number of cases
means that this finding is more reliable. The most startling result was that of horses
that have some form of respiratory stridor being approximately 13 times more likely
to show PRDS. This has to be related to the marked nasal cooling that occurs in the
horse due to its high ratio of upper respiratory tract surface area to brain mass
(McConaghy et al.1995). Any restriction in air flow must affect this, leading to
increased cerebral hyperthermia. The acute hind limb discomfort exhibited by some
horses may be ascribed to the rerouting of blood supply to the skin and respiratory
tract away from the muscles when the horse becomes hyperthermic (McConaghy et
al. 2002). The resultant hypoxia to the muscles could result in the symptoms
experienced.
The importance of environmental factors and the various risk factors that have been
identified shows that it may be possible to predict which horses are likely to show
PRDS. This could help in the management of the syndrome leading to a reduction in
its prevalence.
REFERENCES
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8. Stull CL and Rodiek AV. Physiological responses of horses to 24 hours of transportation using a commercial van during
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