What is "IR"
"IR" stands for Insulin Resistance
Not to be confused with PPID (pituitary pars intermedia dysfunction) or Cushing's (PCS)
Why am I concerned about IR?
It's strongly associated with horses that have had laminitis
(maybe as a reason for A. causing it or B. how they react to diet after laminitis)
The science of it-for the nerds like me:
Physiology Review- taken from online www.ivis.org
Insulin is a hormone secreted by the pancreas that stimulates the uptake of glucose by tissues when
sugar is abundant (i.e., after feeding). Skeletal muscle and adipose tissues are the major sites of
insulin-mediated glucose uptake, but the liver also
responds to insulin by increasing the uptake of glucose from the blood.
Insulin binds to receptors on the surface of plasma membranes.
It triggers aseries of internal events that results in the movement of glucose-transporter proteins (GLUT4) to the
cell surface, which facilitates rapid glucose uptake.
Insulin plays an important role in the storage of energy by moving glucose into cells where it can be
stored as glycogen or converted into fat.
This condition is deﬁned as the failure of tissues to respond appropriately to insulin.
There are numerous mechanisms responsible for IR including reduction in the density of i
nsulin receptors on the cell surface, malfunction of insulin receptors, defects in
internal signaling pathways, and interference with the translocation or function of GLUT4 proteins.
IR and Laminitis
All of the pieces of the puzzle must be assembled
before we can fully understand the association between IR and pasture-associated laminitis in horses
and ponies. There are two broad mechanisms by
which IR could pre-dispose horses to laminitis:
(1) insulin resistance might impair glucose delivery
to hoof keratinocytes, or (2) insulin resistance could
alter blood ﬂow to the foot. The ﬁrst theory is supported by results of a study performed by Pass et al
in which it was shown that hoof tissue explants kept
in culture separate at the dermal-epidermal junction when deprived of glucose.
Furthermore, GLUT4 proteins
are found in equine keratinocytes, which suggests
that insulin-stimulated glucose uptake occurs in the
hoof. Studies examining the relationship between
IR and blood ﬂow have not been performed to date in
horses; however, insulin is known to act as a slow
vasodilator in humans, and IR has been associated
with a decrease in peripheral vasodilation.
If IR is a determinant of susceptibility to pastureassociated laminitis, then what triggers the laminitis episode itself? It seems that non-structural
carbohydrates (NSC) within pasture grasses play an
important role in this process. Most NSC measurements include simple sugars, starch, and fructans
(polymers of fructose), and levels of these components vary considerably within grass according to
geographical location, soil type, weather conditions, and time of day.
NSC are likely to affect the susceptible horse in two ways. First, excessive sugar
consumption could exacerbate IR like it does in diabetic humans. Second, consumption of large
quantities of NSC might alter the bacterial ﬂora
found within the large intestine. These alterations
in bacterial ﬂora are thought to increase the production of as yet unidentiﬁed triggering factors for laminitis that may include exotoxins, endotoxins, or vasoactive amines.
Alterations in large intestinal bacterial ﬂora have been induced by orally administering oligofructose (a fructan) to horses.
Here is another great site to read for IR and why it's becoming more prevalent in our horses
Yea, welcome to my world.
To simplify-there are reasons things happen.
I'm trying to figure out WHAT caused Laz's laminitis.
Was it Putomac? If so, that means he didn't have an IR reaction to grass that caused his laminitis.
If so, is he now considered a true IR horse, or non IR?
Did that bout make him more susceptible to becoming an IR horse?
Laminitis to me, is like Pneumonia. Once you have it, you can get it again much easier so I want to have all the answers I can to allow for his diet to be catered to his needs and his health.
Here are some easy symptoms to look for if you suspect your horse may be IR and shows signs of foot sore:
patchy fat (sholders, rump, elbows, neck)
orbital eye fat
stretched white line
According that list, Laz has the last two symptoms, so we MAY be lucky and he may not be IR, which will help me adjust his lifestyle/diet.
If you think your horse's feet are sore-start dissecting their diet (and trim).
They are RELATED completely. Not always (but so so so often!!!)
Luckily, I have Michigan State University so close to us, and they are one of the TOP schools for Animal Science
The IR test that I am doing is THIS
There is so much more to IR and diet and horse's hoof health, this post could go on for hours. Many of you could add to this, and please feel free!!!