Sticky Blood in Horses
Sticky Blood in Horses
Most people in the horse industry already know that horses are natural blood dopers. This is because horses hold a reserve of red blood cells in their spleens and release the extra cells into the bloodstream as soon as they start running. This remarkable quality has been well-established by veterinarians and biologists as a key trait that enables horses to be superior athletes. What is not so well-known is that the horses’ red blood cells also behave differently than other animals. They are stickier. When both horses and humans are at rest, the thickness (packed cell volume, PCV, or Hct) of horse blood is similar to human blood; however the red blood cells of horses are more rigid and stickier than human red blood cells .
In a scientific study of five different species of mammals, the red blood cells of horses were shown to stick together (or aggregate) much more than humans, rats, rabbits, and guinea pigs . This study was conducted with the red blood cells immersed in the animal’s own plasma and then repeated with the blood cells washed in buffered saline and in dextran solution. The horses’ red blood cells were shown to be stickier than any of the other mammals, regardless of the suspended fluid solution. The data showed that the increased aggregation is partly due to the behavior of the equine red blood cells and red cell membranes .
A study published in the American Journal of Veterinary Research by a team of scientists at the University of Tennessee found that equine red blood cells stick together more than four times faster than human red blood cells. They found that the proteins in equine blood plasma also contribute to stickiness. The fibrinogen molecules in horse blood were shown to be 40% more massive than those in humans, dogs, and cattle, causing equine red blood cells to stick together much more . Fibrinogen is a key protein in the formation of blood clots. Increased fibrinogen levels cause blood viscosity to increase. The Tennessee researchers wrote: “By measuring blood viscosity at high and low shear rates, the rheologic behavior of blood can be evaluated and possible flow anomalies can be detected.” They also noted: “Measurement of blood viscosity and evaluation of the rheologic properties of horse blood may aid in detection of diseases affecting blood flow in horses.” 
Blood viscosity is a rich measurement that can be used to characterize individual horses. The Equine Blood Viscosity Test reports both the systolic and the diastolic blood viscosity scores for each blood sample we receive at our lab. This enables us to provide data for both the thickness and the stickiness of each horse’s blood specimen.