surfaces. The prevalence of PRDS at the Kimberley racecourse, which only has a
sand track, was 0.17%, which is lower than the overall prevalence of 0.23%. The
prevalence of PRDS increased significantly with race distance (Fig 3). The
prevalence of PRDS was significantly higher in horses older than 2 years. The
relative risk of PRDS associated with 3 year olds competing was 2.56 (P<0.0001), of
4 year olds competing was 3.14 (P<0.0001) whilst that of 5 year olds and older
competing was 2.53 (P<0.0001) when compared to 2 year olds (Fig 4). The
prevalence of PRDS was significantly higher in males than in females (RR=1.21,
P=0.003). The relative risk of PRDS on good going was 2.19 (P<0.0001) and on soft
going was 2.57 (P<0.0001) when compared to horses racing on firm going. A smaller
analysis of the population over 5 years from the 1st of August 2008 to the 31st of July
2013, showed a significant increase of PRDS in horses transported to the
racecourse, when compared to the average number of horses transported annually
(RR=1.19, P<0.0001). The relative risk of PRDS for horses competing during the day
was significantly higher than when racing at night (after 18h00) at the Newmarket
Racecourse over the period September 1996 to April 2007 (RR=3.15, P<0.0001).
However, there was no significant difference for horses competing after 18h00 at the
Turffontein Racecourse over the period November 2009 to August 2013. The relative
risk of a horse with a history of respiratory stridor showing PRDS as well, was 13.03
(P<0.0001). The prevalence of PRDS in horses that wore blinkers during races was
no different to those that do not wear blinkers. When looking at possible hereditary
factors, it was found that 37.1% of the cases of PRDS were sired by 10.7% of
stallions.
DISCUSSION
This syndrome is associated with some very specific clinical signs and symptoms
and it was for this reason that it was decided to expand the definition to include those
cases showing respiratory stridor as well as those that show acute discomfort of the
hind limbs. As the name implies, this syndrome only manifests itself post-race and is
never seen during training, nor is it reproducible on a treadmill. It would appear that
the added stress of racing plays an important role and certain horses appear to be
more susceptible than others. The fact that 10.7% of stallions have sired 37.1% of
PRDS horses indicates that there is possibly a hereditary link that requires further
investigation.
The primary form of treatment, is to hose the horses down with cold water and allow
them to drink. Kohn et al. (1999) have shown that active cooling of the horse has a
significant effect on lowering the core temperature, thereby reducing the symptoms.
The rapid response to cooling by hosing in approximately 80% of cases, confirms
how effective thermoregulation by sweating is in the horse. It has been observed that
removal of the bridle and placement of a head-collar often encourages the horses to
relax their jaw and drink. When there is not a rapid response to hosing, then the
parenteral administration of soluble corticosteroids is recommended. Two 10ml vials
of Solu-Delta-Cortef (Zoetis) containing 10mg of Prednisolone p er ml is usually
sufficient, but may be repeated if necessary. Correction of the dehydration with rapid
infusion of large volumes of parenteral fluids like a balanced poly-ionic solution
(Ringer’s Lactate) may be indicated. An infusion of a 4.2% sodium bicarbonate
solution is also effective in cases not responding to treatment. The judicious use of
Proceedings
of
the
South
African
Equine
Veterinary
Association
Congress
2016
28