Endurance
riding places exceptional demands on horses, particularly during competitions
held in hot weather over
long distances. Maintaining hydration and electrolyte
balance is therefore a major concern for riders and veterinarians.
As
a result, administering intravenous (IV) fluids before competition has become
increasingly common, especially at major endurance events where horses are
expected to compete in high temperatures, over difficult terrain, or under
conditions that increase the risk of dehydration.
Despite
its popularity, however, there has been little scientific evidence to show
whether pre-ride IV fluids actually improve hydration, reduce cardiovascular
strain, or enhance performance.
To
investigate this question, Laura Weintraub and colleagues at Loomis Basin
Equine Medical Center, Penryn, California, conducted a study to determine
whether administering intravenous fluids before an endurance competition
provides measurable physiological or clinical benefits. Their findings have
been published in the Journal of Equine Veterinary Science.
The
researchers hypothesised that horses receiving IV fluids the day before
competition would be better hydrated and experience less cardiovascular stress
than untreated horses. They expected the treated horses to have lower heart
rates during the ride together with laboratory findings consistent with
improved hydration.
Fourteen
client-owned horses entered in a 45 km endurance ride were enrolled in the
study. The event was held in extreme heat over challenging terrain, providing
an ideal opportunity to assess whether additional fluid support offered any
advantage.
The
horses were randomly assigned to one of two groups. One group received
intravenous fluids the day before the ride, while the control group received no
fluid treatment.
Data
were collected at six time points: before travelling from home, at check-in the
day before the ride, two to three hours after catheterisation and treatment,
one hour before the start, 32 km into the ride, and immediately after
finishing.
At
each assessment, the horses underwent physical examination and blood sampling.
Laboratory measurements included bicarbonate, sodium, potassium, chloride,
calcium, glucose, lactate, blood urea nitrogen (BUN), creatinine, packed cell
volume and total protein. The results were analysed using two-way analysis of
variance (ANOVA).
The
researchers found only minor differences between the two groups.
Horses
that received IV fluids had lower total protein concentrations shortly after
treatment, reflecting the expected short-term dilution of the blood following
fluid administration. Blood urea nitrogen concentrations were also lower in the
treated horses at the 32 km checkpoint, suggesting a modest effect on hydration
status or kidney-related blood parameters during exercise.
However,
these changes did not translate into clinically meaningful benefits.
Heart
rate, one of the most important indicators of cardiovascular effort and
recovery in endurance horses, was similar in both groups. Horses receiving IV
fluids had a mean heart rate of 36 ± 5 beats per minute compared with 39 ± 3
beats per minute in the untreated horses, a difference that was not
statistically significant.
Overall,
the study suggests that while pre-competition IV fluids can produce measurable
changes in some blood parameters, these changes are small and may have little
practical significance. The reduction in total protein reflects temporary
haemodilution rather than improved fitness for exercise, while the lower BUN
concentration observed during the ride was not accompanied by improved
cardiovascular responses or other indicators of enhanced performance.
The
findings therefore challenge the assumption that routinely administering
intravenous fluids before competition benefits healthy endurance horses. In
this study, pre-ride fluid therapy did not reduce cardiovascular strain,
improve heart-rate recovery, or produce widespread improvements in laboratory
markers of hydration.
For
veterinarians, riders and event organisers, the study provides valuable
evidence when considering the routine use of pre-competition IV fluids. Fluid
therapy requires veterinary supervision, venous catheterisation, specialised
equipment and additional time. If it offers little measurable benefit in
healthy horses, its routine use as a preventive hydration strategy may not be
justified.
These
findings do not mean intravenous fluids are never appropriate. Horses showing
clinical signs of dehydration, heat stress, illness or poor recovery may still
require fluid therapy as part of their veterinary treatment. However, this
study suggests that administering IV fluids simply because a horse is about to
tackle a demanding endurance ride may provide far less benefit than many riders
and veterinarians have assumed.
For
more details, see:
Weintraub, L., Fielding, C. L., Carli, I.,
& Greene-Dittz, G.
The effect of intravenous fluids administered
prior to competition: A randomized clinical trial.
Journal of Equine Veterinary Science,(2026) 106121.
https://doi.org/10.1016/j.jevs.2026.106121