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Existing reports on sperm structure in the emu do not adequately illustrate or describe all the salient ultrastructural features necessary for a meaningful comparison of normal and abnormal sperm in this species. As sperm morphology forms an important parameter in determining semen quality, and in view of the proposed role of artificial insemination in the farming of ratites, this article re-evaluates and complements the existing data on the topic, provides a fully illustrated description of emu sperm ultrastructure, and documents some unreported morphologic features. Conventional transmission and scanning electron microscopy and high resolution scanning electron microscopy were used to describe the ultrastructure of sperm harvested from the distal deferent duct of sexually mature birds slaughtered during the breeding season. In addition to broadly confirming the basic ultrastructural characteristics previously described for emu sperm, this study revealed a number of unreported morphologic features. These included distinct differences in surface properties between the acrosome and nucleus, the presence of a thread-like appendage near the base of the nucleus, variable positioning of the annulus relative to structures located at the midpiece-principal piece junction and regional differentiation of the principal piece. Although the emu displayed similar basic morphologic features to sperm of other ratites and the tinamou, marked structural peculiarities were obvious, notably the lack of an endonuclear canal and a perforatorium and the presence of significantly more mitochondria in the midpiece coupled with an absence of intermitochondrial cement. Although the broad morphologic features of emu sperm would appear to add credence to the general view that the ratites, together with the tinamous, form a monophyletic group at the base of the avian phylogenetic tree, it is also clear that emu sperm are distinctly different from those of the ostrich, rhea, and tinamou which together share morphologic affinities. This observation may lend some support to the alternate view that the Australasian ratites represent a separate clade that developed independently from flightless ancestors., (Copyright © 2014 Elsevier Inc. All rights reserved.)

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., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Abaxial tail implantation is a defect occurring in the neck region of spermatozoa and is characterized by misalignment of the centriolar complex relative to the head base. This defect has been described in a number of mammalian species, but is rarely reported in birds. In this study, a detailed description of the defect in emu sperm is presented as well as morphological evidence of its origin in the testis. Despite their low incidence defective sperm could readily be identified using light (LM) and transmission electron microscopy (TEM). Affected sperm displayed obvious misalignment of the head and flagellum with many cells additionally showing unilateral swelling and caudal extension of the nuclear base. This material overlapped the anterior aspect of the centriolar complex. More subtle forms of the defect which were not resolved by LM were revealed by TEM. Abaxial sperm development could be identified in the testis during the early elongated spermatid stage of spermiogenesis. At this stage the centriolar complex was clearly misaligned with respect to the longitudinal axis of the condensing and elongating nucleus. The rare occurrence and low incidence of this defect in the emu would suggest that it has little effect on fertility., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Little detailed information is currently available on the incidence and morphological characteristics of abnormal sperm in the emu (Dromaius novaehollandiae) and of ratites in general. This situation is further compounded by the lack of a uniform system for the morphological classification of avian sperm defects. Considering the important role that sperm morphology plays in the assessment of semen quality, a detailed description of avian sperm defects is of paramount importance. Based on morphological data provided by light and electron microscopy, a mean of 17.3% abnormal sperm was recorded in semen samples collected from the distal deferent duct of four adult emus during the middle of the breeding season. Four categories of defects were identified. Head defects (57.2% of total defects) consisted of bent heads, macrocephalic heads, round heads and acephalic sperm. Zones of incomplete chromatin condensation and retained cytoplasmic droplets appeared to be implicated in head bending, while giant heads were often associated with multiple tails. Acephalic sperm revealed a complete tail devoid of a head which was replaced by a small spherical structure. Tail defects (22.6% of total defects) were subdivided into neck/midpiece defects and principal piece defects. In the neck/midpiece region disjointed sperm were the exclusive defect noted and were characterized by the complete separation of the head and midpiece in the neck region but within the confines of the plasmalemma. Defects observed in the principal piece were subdivided into short tails, coiled tails and multiple tails. No conclusive evidence was obtained that tail coiling represented the 'Dag' defect. Biflagellate sperm were the most common form of multiple tails, demonstrating two complete tails with all the normal structural elements. Cytoplasmic droplets (13.9% of total defects) were classified as a separate defect. The location and eccentric positioning of retained cytoplasmic droplets was similar to that described in ostrich sperm although the composition of the droplets differed markedly between the two species. A small percentage of sperm (6.3% of total sperm defects) displayed multiple abnormalities. Based on these findings we propose a morphological classification for abnormal ratite sperm identifying head and tail defects, with additional categories for cytoplasmic droplets and multiple defects. Each category is further subdivided to reflect a range of specific defects within the category. It is envisaged that additional defects will be added to each category or that new categories may be added as future studies on the detailed morphology of avian sperm defects are completed., (Copyright © 2011 Elsevier Inc. All rights reserved.)