Blood Viscosity and Colic

Colic is a general term we use to describe abdominal pain. Although colic can be caused by a disruption in any of the abdominal organs, the most common cause in horses involves the gastrointestinal tract. The National Animal Health Monitoring System (NAHMS) Equine '98 study conducted by the USDA estimated a colic incidence of 4.2/100 horses per year [1]. After old-age, colic is the second most likely cause of death in horses. Additionally, the total cost estimate for colic during 1998 was $115 million.

Horse with Colic

Research published in the Journal of Veterinary Internal Medicine suggests that horses with colic may be more susceptible to tissue damage caused by impaired blood flow and regional perfusion [2].

The researchers compared blood viscosity of normal horses with two other groups of horses presenting for colic surgery: one group which died during surgery and another which survived. After correcting for packed cell volume (PCV), a significant determinant of blood viscosity, horses who died during colic surgery had significantly higher (more than two standard deviations) blood viscosity than those who did not as well as the clinically normal horses.

It is not known whether impaired blood flow can be a direct cause of colic, or if the reverse is true, that is, the condition of colic results in impaired blood flow. However, the study described above did demonstrate a strong link between blood viscosity and the survival rate of horses undergoing surgery for colic.

Inflammatory disorders and ischemia from twisting and strangulating of the intestines are both common causes of colic which are associated with increased blood coagulation (clotting) and an impaired ability to break down blood clots [3]. When blood viscosity increases, the blood becomes thicker and stickier, and it is more likely to restrict blood flow and form clots in small vessels and capillaries. These are the vessels which are most affected in horses with colic caused by ischemic intestinal disease [2].

Tissue injury as a result of poor blood flow and impaired circulatory performance determine the survival outcome of horses with colic during surgery [4]. Consequently, measuring blood viscosity for horses ahead of surgery may be an important predictor of surgery outcomes in horses with colic.

Blood viscosity may also be able to help manage the progression of colic and other conditions related to increased blood viscosity such as navicular disease and lameness [5], as well as exercise-induced pulmonary hemorrhage and exertional myopathy [6].

1. USDA. National economic cost of equine lameness, colic, and equine protozoal myeloencephalitis in the United States, 2001. USDA APHIS Veterinary Services National Health Monitoring System Fort Collins, Colorado.

2. Andrews, F.M., R.L. Hamlin, and P.S. Stalnaker, Blood viscosity in horses with colic. J Vet Intern Med 1990; 4:183-6.

3. Monreal L, et al. Hypercoagulation and hypofibrinolysis in horses with colic and DIC. Equine Vet J 2000; 32:19-25.

4. Puotunen-Reinert A. Study of variables commonly used in examination of equine colic cases to assess prognostic value. Equine Vet J 2010; 18:275-7.

5. Amin TM, et al. Effects of warfarin on blood rheology in navicular disease. Res Vet Sci, 1986. 40(3): p. 308-12.

6. Boucher JH, et al. Erythrocyte alterations endurance exercise in horses. J Appl Physiol 1981; 51:131-4.