The results of this study prevented a comparison between the platelet gels (fibrin clots) obtained from the activated PC of dogs and cats. The ultrastructural differences observed within each species show that there are differences in both platelet response and fibrin polymerization. In addition, the platelets from cats and dogs are quite different. The size of the cat platelets (diameter 2–6 mM, mean platelet volume 8.6-14.1 fL) [18, 19] differs from the size of the dog platelets diameter (1–3 mM, mean platelet volume 8.4-11.5 fL) [20, 21], and more complex factors such as glycoprotein receptors and signal transduction pathways might be involved in the structural platelet responses observed in our study .
According to Sweet et al., platelet shape is approximately elliptical, and the ratio between the minor and major axes is 0.5. Mody and King  thought that, in general, the elliptical shape is determined by the ratio between the minor and major axes, which is always <1, but when this shape becomes more elongated, the ratio is reversed so that the determination is being made by the ratio between major and minor axes, which is always >1 . In our study, the platelets from cats activated with calcium gluconate show a ratio between minor and major axes of 0.5, and they show a ratio between major and minor axes of 2.28. The cat platelets activated with batroxobin show a ratio between minor and major axes of 0.60 and a ratio between major and minor axes of 1.86, which puts them closer to the elliptical shape. This suggests a greater change of the elliptical shape in platelets activated with calcium gluconate.
Cat platelets activated with CGB occupied a greater percentage of total area than platelets activated with CG, and they also had a greater number of α-granules in their cytoplasm. These findings, along with the relationships between the axes, suggested a moderate degree of platelet activation [23, 24].
Platelet gel from dogs activated with CG presented fibrin fiber widths of 209.4 nm and 172.6 nm. These findings are within the range described for thick fibers in horses (150–250 nm), human beings (203–441 nm), monkeys (143–309 nm), oryxes (160–338 nm), sheep (169–286 nm), penguins (182–391 nm) and sea turtles (130–400 nm) . However, Pretorius et al. used scanning electron microscopy and did not provide information about the ultrastructural characteristics of the platelets contained in the PRP.
Pretorius et al.  also described the fine and intermediate fibrin fibers for the aforementioned species. However, these kinds of fibrin fibers were not observed in our study. This may indicate that canine platelet gel from PC activated with either CG or CGB produces only fibrin fibers of higher quality compared with other species (Pretorius et al.  used thrombin as an activating substance). However, our results show that CGB produces thinner fibrin fibers than those from human PRP activated with thrombin . Our results clearly demonstrate that the activating substance influences the quality of the resulting biomaterial (biodrug).
The smaller area and percentage area of intercellular space observed in the fibrin clots from canine PC activated with calcium gluconate suggest greater cell aggregation. These findings, in conjunction with the greater area and percentage of area of fibrin fibers and the greater width of the fibrin fibers, indicate a strong degree of platelet activation with rapid formation of fibrin clots, and the fibers in these clots are thicker than those from PC activated with CGB. It is important to consider that platelet activation induced by CG is the result of two different signaling events: the direct effect of Ca2+ on platelets  (after saturation of the calcium antagonist ACD) and the effect of autogenously generated thrombin via Ca2+ dependent activation of the coagulation pathway .
We are not aware of reports that describe the ultrastructural characteristics of platelet gels from dogs and cats, but the general findings of this study indicate that, regardless of the substance used for PC activation, cat platelets require a longer incubation time than dog platelets to reach the type IV morphological classification .
The differences observed between dog and cat clots activated with either CG or CGB could depend on the mechanisms of action of the two activating substances. It is known that batroxobin does not activate platelets trapped within the fibrin network . In this study, however, batroxobin was reconstituted with calcium gluconate, and the amount of calcium was proportionally less when PC was activated only with calcium gluconate. The results observed in this study corroborate the fact that, when batroxobin is used for PC activation, there is no massive release of the contents of platelet alpha granules, in contrast with the effect produced by the calcium salts alone .