Fine structure of the fibrous sheath of stallion sperm tails.

The research is focused on the detailed analysis of the structure and development of the fibrous sheath in the sperm tails of stallions. The key highlight is that these structures are not unique to the stallions but are common among many other mammalian species.

Methods

• The researchers obtained material from the testis and the cauda epididymidis of three normal stallions through slaughter or castration.
• The samples were fixed in a 2% buffered solution of osmium tetroxide with sucrose, as recommended by Millonig (1961). They were then embedded in Epon which is a standard practice in similar examinations.
• To accentuate the visibility of the structures, some blocks were treated with 1% phosphotungstic acid in alcohol during this procedure.
• Thin sections were stained with uranyl acetate, a routine electron microscopy procedure, to help visualize these microstructures under a Siemens Elmiskop I microscope.

Findings

• The development of the fibrous sheath in horse spermatozoa was observed to be consistent with Nicander’s (1962) description for other mammals. It begins during the cap phase of spermiogenesis.
• Two longitudinal strands of opaque material were observed to form inside the plasma membrane along fibers 3 and 8 of the tail primordium. Over time, these strands were seen to interconnect by numerous semicircular ‘ribs’ of similar density, forming longitudinal pillars connected by coarse ribs.
• In cross-sections, these pillars appeared as slight thickenings of the fibrous sheath, most distinct in the proximal part of the principal piece. The sheath itself had spaces which suggested defects in the ribs, a pattern seen also in immature testicular spermatozoa.

Conclusions

• The fibrous sheath in horse spermatozoa does not have any special features and its structure and development is found to resemble other mammalian species.
• The perceived ‘defects’ in cross-sections of horse sperm tails were found to be due to the oblique course of many ribs and the unusually broad interspaces between them.

The research concludes that the fibrous sheath in stallion sperm tails is structurally similar to those present in other mammals, in line with previous quite similar research. Moreover, the appearance of ‘defects’ in these structures is attributed to the positioning and spatial arrangement of the components rather than to actual anomalies in the structure itself.