Hypocoagulability is associated with a poor prognosis in horses presenting with colic. Thrombelastography (TEG®) is a stall-side test that can be used to rapidly evaluate citrated blood samples for evidence of coagulopathy. Tissue factor (TF) may be added to speed the initiation of clot formation for TEG® analysis. TEG® was evaluated in citrated blood from 16 normal horses 30 minutes after collection using TF-activated (1:100 in 4% bovine albumin) and non-TF activated protocols. The median (range) values for TF-TEG® were R = 7.2 (3-10) min, K = 2.8 (1.5-5) min, Ang = 55 (40-67) deg, and MA = 62 (53-68) mm. The median (range) values acquired for non-TF TEG® were R = 14 (9-25) min, K = 3.6 (2-10) min, Ang = 48.1 (28-64) deg, and MA = 59 (51.6-69) mm. R values were significantly different between TF and non-TF TEG® protocols (p < 0.01), illustrating the effect of TF on initiation of coagulation. The remaining TEG® variables were not significantly different between the two protocols, indicating that either technique is suitable for evaluating these characteristics. R values in both groups were significantly different between two operators (and cohorts of horses; p = 0.01). Non-TF K and Ang values were also different between operators (p < 0.01), a distinction that was not true for the TF-activated parameters. It is prudent to perform both TF- and non-TF-activated TEG® when evaluating horses for coagulopathies. Use of TF as activator may minimize inter-operator variability.