Objective—To determine lactate breakpoint of horses
and test for effects of training and dietary supplementation
with corn oil on that breakpoint.
Animals—7 healthy Arabian horses.
Procedures—Horses received a control diet (n = 4) or a
diet supplemented with 10% corn oil (4). A training program,
which comprised two 5-week conditioning periods
with 1 week of rest, was initiated. Submaximal
incremental exercise tests (IET) were conducted before
the first and after both conditioning periods. Blood samples
for determination of blood lactate and plasma glucose
concentrations were collected 1 minute before IET
and during the 15 seconds immediately preceding each
speed change. Data collected were fit to one- and twoslope
broken-line models and an exponential model.
Results—Good fits were obtained by application of
the broken-line models (adjusted R2 > 0.92) to blood
lactate concentration versus speed curves. Lactate
breakpoints increased 41% after training but were
not affected by diet. After training, slope 2 and peak
blood lactate concentrations were greater in the corn
oil group, compared with controls. Mean blood lactate
concentration at the breakpoint was not affected by
training or diet. Plasma glucose concentration versus
speed curves also fit the broken-line models, and glucose
breakpoints preceded lactate breakpoints by
approximately 1 m/s in the second and third IET.
Conclusions and Clinical Relevance—Lactate
breakpoints can be determined for horses, using
blood lactate concentration versus speed curves generated
during submaximal IET and may be useful for
assessing fitness and monitoring training programs in
equine athletes. (Am J Vet Res 2000;61:144–151)