Light microscopic features and morphometry of sperm in the emu (Dromaius novaehollandiae)

A comprehensive morphologic description of emu sperm at the light microscopy level, an essential prerequisite for the routine evaluation of semen quality in this species, is not currently available. In this study, sperm morphology and morphometry were evaluated using conventionally prepared Romanowsky-stained semen smears of samples collected from the distal ductus deferens from 15 adult birds and fixed in 2.5% glutaraldehyde. Examination of the smears using phase contrast under 100× magnification readily resolved the various components of the cell, namely, the acrosome, nucleus, midpiece, principal piece, and endpiece. This technique was simple to use and produced consistently reproducible results. Normal emu sperm were typically filiform in appearance and closely resembled sperm of the ostrich and other non-passerine species, particularly poultry. A previously undescribed cytoplasmic appendage, associated with the base of the head, was a novel morphologic feature. The acrosome was short (1.84 ± 0.31 μm; mean ± standard deviation), whereas the nucleus measured 11.77 ± 0.93 μm in length. The length of the segments of the flagellum were 2.91 ± 0.4 μm for the midpiece, 47.45 ± 2.8 μm for the principal piece, and 3.69 ± 0.82 μm for the endpiece. The total sperm length was 67.64 ± 3.13 μm (range, 60.14-79.49) and the head:tail ratio was 1:4. Sperm dimensions in the emu were similar to those of other ratites.