ABSTRACT
<p><b>OBJECTIVE</b>To investigate damages to the quality of boar sperm frozen in 5 ml straws, pellet and 0.25 ml straws as well as the ultrastructural changes of frozen boar sperm in 5 ml straws.</p><p><b>METHODS</b>We compared 3 different freezing packages of 5 ml straws, pellet and 0.25 ml straws to determine their effects on frozen boar semen, and observed the morphological and ultrastructural changes of the boar sperm in the 5 ml straws using scanning electron microscopy.</p><p><b>RESULTS</b>In the 5 ml straws, the vitality and motility of the boar sperm after freezing were not significantly different from those in the other two formulations, the normal apical ridge (NAR) was 52.65%, higher than in the pellet but not significantly different from that in the 0.25 ml straws, and the sperm membranes were mostly bubbly, some locally broken, which indicated the damage induced by freezing and thawing.</p><p><b>CONCLUSION</b>At the present time, boar semen frozen in 5 ml straws were not significantly different from those frozen in 0.25 ml straws. The existing freezing-thawing method may cause certain damage to the quality and ultrastructure of boar sperm, and therefore needs to be further improved.</p>