Ultrastructural description of fresh and frozen/thawed sperm derived from collared peccaries (Pecari tajacu Linnaeus, 1,758).

The aim was to describe, through scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the ultrastructure of peccaries' fresh and frozen-thawed sperm. For that, semen derived from three mature males was obtained by electroejaculation and evaluated for motility, membrane integrity, membrane functionality, chromatin integrity, and morphology through light microscopy. Samples were frozen using a Tris extender plus egg yolk (20%) and glycerol (6%). Then, fresh and frozen-thawed semen samples were mixed in different sperm pools that were processed for SEM and TEM. Sperm motility, membrane integrity, and functionality were impaired (p < .05) by freezing-thawing procedures, but sperm morphology, and chromatin integrity evaluated by light microscopy were not significantly affected. The SEM revealed that peccaries' sperm presents a flattened head in a paddle format, measuring 6.07 μm in length and 3.84 μm in width, with a vastus acrosome (4.46 μm). Normal tails measure 38.11 μm, being formed by an extensive midpiece with 15.52 μm in length. In frozen-thawed samples, both SEM and TEM provide us information about damage undetected through light microscopy as the presence of vesicles in the acrosome, loose plasma membrane, vacuolized mitochondria, dense fibers disorganized, and decondensed chromatin. In conclusion, we provide the first description of the sperm ultrasctruture in collared peccaries. Moreover, SEM and TEM help us to identify some nanometric damage provoked by freezing-thawing procedures, thus providing valuable information for the improvement of such important protocols used for biobanking formation.