Abstract
A rare case of a fertile boar with pale brown semen is reported. The semen was normal except for the color. The spermatozoa, pale brown in color, and the testis were examined by light and electron microscopes. With the light microscope a few dots, about 0.3 μm in diameter, were observed in the head. With the electron microscope 2 types of structures were found in the dots: 1) a myelin-like structure and 2) an electron dense material. Both of these structures were observed just under the cell membrane, the equatorial segment of the acrosome, or the postacrosomal sheath. Other structures of the spermatozoa were normal. No abnormalities were observed in the testis by the light microscope. Spermatids of the maturation phase showed the myelin-like structure. They also showed small vesicles, which seemed to be undeveloped myelin-like structures. The electron dense granules could not be found in the spermatids. Other structures in the testis were normal ultrastructurally. This investigation shows that the myelin-lik e structure observed in the spermatozoa first appeared in the spermatids of the maturation phase. The electron dense granules seemed to be derived from the myelin-like structure after spermiation. The cause for the color of the spermatozoa is not known.
