Walking On Volume 2, Issue 1, January 2015 | Page 8
For the Health of It
Changing Tides in
Insulin Resistance Interpretation
Reprinted with permission from the April 2013 issue of Equine Disease Quarterly
8 • Walking On
Blister beetle (Epicauta spp.) poisoning occurs
in hIn 1999, I was told, “Everyone knows blood
insulin and glucose are too variable to be of any
use.” However insulin resistance (IR) and Equine
Metabolic Syndrome (EMS) have been the focus of
much research for the past 10 years and blood insulin and glucose levels do have their purposes when
appropriately used and interpreted.
A widespread perception exists that any elevation above “normal” in plasma insulin (hyperinsulinemia) indicates EMS and a significant risk
of laminitis. However, diagnosis is not quite that
simple.
There are indeed a number of factors that
influence fasting glucose and insulin responses to
dextrose or sugar challenges and tissue sensitivity to
the actions of insulin. These need to be taken into
consideration when evaluating an IR/EMS suspect.
We now know that not all obese horses are IR, nor
are truly IR horses/ponies/donkeys at high risk of
laminitis always obese. Stress and acute pain can
also induce IR.
Hyperinsulinemic responses to sugar challenges
and mild fasting hyperinsulinemia are normal in
horses adapted to high starch/sugar feeds. This is
an adaptation that allows rapid return to normal
blood glucose levels after ingestion of high glycemic
index feeds and does not pose a health risk to the
horse. The return to baseline insulin concentrations
is actually faster than in horses not accustomed to
ingestion of grain-based concentrates, so previous
rations need to be taken into consideration.
Researchers use the modified Frequently Sampled Glucose/Insulin Tolerance (FSGIT) test as the
gold standard for determining insulin sensitivity
and detection of changes in experimental models.
However, this test is impractical for field use. Low
dose (0.25 gram dextrose/kg or 0.15 ml Karo Syrup/
kg) sugar challenges are now recognized to be
more reliable physiologic and sensitive measures of
insulin sensitivity. The challenge is given orally in
the morning and blood is drawn before dosing and
then 60 and 120 minutes later. “Normal” peak glucose and insulin concentrations at 60 minutes are
not well established but can be as high as 180 mg
glucose/dl and 60 μIU insulin/ml, respectively. At
120 minutes both should be lower but not necessarily returned to baseline levels. If there is hyperglycemia and hyperinsulinemia with a slow clearance,
a horse may be at risk of IR/EMS and starch/sugar
intakes may need to be restricted.
Much more research is needed into the physiology and epidemiology of these diseases.
–Dr. Sarah Ralston,
(848) 932-9404, [email protected]
Department of Animal Sciences,
SEBS, Rutgers
The State University of New Jersey,
New Brunswick, New Jersey