The Harry M. Zweig Memorial Fund for Equine Research

Indices of Intra-Abdominal Fibrinolysis in Colic Foals: Pathogenic and Prognostic Markers

Dr. Susan Fubini

FubiniAcute abdominal disorders are common in adult horses and foals. However, published case series and clinical experience reveal that the prognosis for foals following abdominal surgery is less favorable than for adults. The poor surgical outcome for foals is largely due to the formation of intra-abdominal adhesions.

Intra-abdominal adhesions form following an injury to the lining of the abdominal cavity or to the intestine itself. The nature of injury varies, and can include parasite-induced or traumatic disruption of blood supply to the intestine, dietary indiscretions, foreign material in the abdominal cavity, and traumatic or surgical insult to the delicate intestinal wall.

While the inflammatory reaction is necessary and integral to the healing process, inflammation leads to the deposition of sticky inflammatory material (fibrinogen) that matures into a firm meshwork of fibrous strands if not completely cleared by the process of fibrinolysis. The fibrous strands can subsequently limit mobility or completely entangle the bowel, leading to pathologic adhesions that obstruct or “kink” the intestine. This can lead to another colic episode with risk of decline in the horse’s condition or the need to re-operate, and ultimately to death or euthanasia.

We recently conducted a small pilot study (supported by The Dean’s Fund) to examine indices that measure fibrin deposition and lysis in the abdominal fluid and plasma of foals <6 months of age. The study consisted of 3 groups: healthy foals (n=6), foals euthanized because of a non-abdominal inflammatory process (n=6), and foals having colic surgery (n=3).

In spite of low numbers, we found that foals with colic had a dramatic increase (11 fold) in the fibrinogen concentration of their abdominal fluid. This finding was statistically and clinically significant because fibrinogen is the immediate precursor of fibrin, the substance that forms fibrous adhesions. We also found that the measurable indices that promote and result from the breakdown of fibrin (plasminogen and D-dimer) were increased by only two-fold in the colic group. These results indicate a shift in hemostatic balance within the abdomen favoring fibrin deposition. In contrast to the differences in peritoneal fluid fibrinolysis, the values obtained from blood samples did not significantly differ between colic foals and the other 2 groups.

Our pilot study in foals showed some similarities and some differences with previous studies of adult horses. A study by Collatos and coworkers (1) found that adult horses with colic had significant increases in abdominal fluid fibrinogen and plasminogen levels compared with healthy controls. However, the magnitude of increase for these two indices was proportionate in adults. Furthermore, adult horses had a small relative increase of abdominal fluid fibrinogen (2 to 3 fold), compared with the foals’ observed 11-fold increase in abdominal fibrinogen (in our study).

Our findings suggest that high fibrinogen in the abdomen of foals with colic provides an excess of substrate for fibrin formation, while at the same time the foals’ abilities to lyse or clear fibrin is less effective than adults. This would ultimately put foals at risk for intra-abdominal adhesions and further complications.

In our proposed project, we aim to confirm the findings of our pilot study by increasing the number of healthy and colic foals evaluated. In addition, we will compare our foal data with that obtained from adult horses, using consistent sample collection and assay procedures. (Given the different methodologies in previously published reports, it is difficult to make valid comparisons using historical data.) In this larger sample set (n= 40) we will also examine the relationship of the various laboratory indices of fibrinolysis with the clinical outcome of the adult and foal colic cases. In contrast to assays performed on blood samples, direct measures of abdominal fibrinolysis may provide more clinically relevant data to develop prognostic indicators and ultimately guide post-surgical management of equine colic.