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VETERINARY VIEWS
mucous membrane color, particularly in the presence of fluorescent lights, a flashlight,
or in dim or dusk ambient light conditions. Regardless of activity, whether a horse is resident on the farm, used in casual recreation, or participates in extreme exercise stress, pre-existing conditions may confound mucous membrane evaluations. Evaluation can also be difficult in horses that object to anyone looking in their mouths and poking around on their gums.
CAPILLARY REFILL TIME
Finger pressure on a horse’s gums blanches away the color as blood is pushed aside in that location. The membranes should pink up again as blood refills within 1 - 2 seconds, referred to as capillary refill time (CRT). This measures the amount of circulating blood volume and blood pressure. Refill time varies slightly, dependent on the amount of pressure exerted by a pressed fingertip. Mucous membrane color evaluated with the CRT is a fundamental hydration factor evaluation that directly correlates to perfusion of other body tissues, especially the bowel. This has significant consequences to an exercising horse or to any horse suffering from gastrointestinal disease or colic.
When assessing mucous membranes, the amount of saliva present on the gums is telling of the degree of hydration in the whole body; a dry, tacky mouth often indicates dehydration.
REFLECTION OF SYSTEMIC HEALTH
Whether a horse experiences dehydration
as he is participating in an athletic event or transport, or is suffering from gastrointestinal disease or any illness, mucous membranes serve as a monitor of the cardiovascular status of the horse. Performance horses not only contend with fluid shifts to demand tissues such as
Putting finger pressure on a horse’s gums takes away the color as blood is pushed from that location. The membranes should pink up within 1-2 seconds as blood refills, referred to as capillary refill time (CRT).
A horse suffering from systemic illness, such as gastrointestinal disease or colic, is at risk of deterioration of the circulatory system. This is often reflected in the color of the mucous membranes.
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heart and muscle for locomotion and brain and kidney for normal homeostasis, but they also must contend with fluid loss as sweat to maintain thermoregulation.
The first aberration of the color of the mucous membranes as a horse dehydrates and/ or responds to fluid shifts is a reddening of
the mucous membranes above the tooth root with a corresponding paleness to the rest of the tissue. This is first appreciated as a disparate color along the membranes, referred to as margination, which casts a purplish or bluish tinge along the line of the teeth while above the gumline appears pale or even normal pink in color.
Circulatory compromise may progress, and if there is limited compensatory adjustment,
the mucous membranes will continue to pale, taking on a bluish tinge, and finally turn a purple, muddy color. Commonly, changes
in mucous membrane color (paling) are accompanied by a delay in the CRT of greater than 1 - 2 seconds. If dehydration and fluid shifts sufficiently compromise perfusion of the cecum and/or large bowel, endotoxemia may affect the capillary beds and result in a “brick red” color to the mucous membranes. Septic
or endotoxic shock causes peripheral vascular beds to open, with increased filling of blood in the capillaries and small vessels. As circulatory shock progresses, less oxygen is sent to the tissues, so this congested blood stagnates, loses its oxygen, and the membranes turn purplish or blue-tinged, then eventually turn to a deathly, muddy-gray.
THE COLICKY HORSE
A horse suffering from systemic illness, such
as gastrointestinal disease or colic, is at risk of deterioration of the circulatory system – this is often revealed by the character of the mucous membranes. Mucous membrane color has
some predictive value for survival but is not a completely reliable parameter. If a colicky horse has pink mucous membranes, studies indicate that there is a greater likelihood of survival
(55%), whereas a horse with toxic, cyanotic, or injected mucous membrane color has a less likely chance of survival (44%). This is not much of a statistical difference, but is more useful following surgery, when membrane color is better correlated with survival probability: If the color is pink after surgery, that horse will likely live.
Determination of survival prognosis in colic cases is better correlated with the CRT. Rough estimates of survival suggest that with CRT