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Photographs of ostrich embryos throughout development, in two-day intervals. Scale bars are marked individually for embryos aged 4–22
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The ostrich (Struthio camelus), the largest living bird, is farmed intensively world wide. However, despite the importance of understanding embryonic development in the ostrich for successful egg incubation practice, little is known about it. Using the chicken model for scaling is currently a common practice in estimating age in ostrich embryos. Th...
Citations
... If artificially incubated, ostrich eggs usually hatch after 42 days [24]. As it was a requirement to end all experiments before hatching, studies were performed on DD 31 and DD 34. ...
... As it is the goal to enable artifact-free imaging of ostrich embryos, repeated experiments in the same animal is desirable in order to reduce the number of embryos used in an experiment. Few differences were present between these two development stages which are predominantly characterized by embryo growth; organogenesis is complete at this late time point [2,24,35]. Namely, significant lower heart rate was observed in Experimental Biology and Medicine ...
In-ovo imaging using avian eggs has been described as a potential alternative to animal testing using rodents. However, imaging studies are hampered by embryonal motion producing artifacts. This study aims at systematically comparing isoflurane, desflurane and sevoflurane in three different concentrations in ostrich embryos. Biomagnetic signals of ostrich embryos were recorded analyzing cardiac action and motion. Ten groups comprising eight ostrich embryos each were investigated: Control, isoflurane (2%, 4%, and 6%), desflurane (6%, 12%, and 18%) and sevoflurane (3%, 5%, and 8%). Each ostrich egg was exposed to the same narcotic gas and concentration on development day (DD) 31 and 34. Narcotic gas exposure was upheld for 90 min and embryos were monitored for additional 75 min. Toxicity was evaluated by verifying embryo viability 24 h after the experiments. Initial heart rate of mean 148 beats/min (DD 31) and 136 beats/min (DD 34) decreased over time by 44-48 beats/minute. No significant differences were observed between groups. All narcotic gases led to distinct movement reduction after mean 8 min. Embryos exposed to desflurane 6% showed residual movements. Isoflurane 6% and sevoflurane 8% produced motion-free time intervals of mean 70 min after discontinuation of narcotic gas exposure. Only one embryo death occurred after narcotic gas exposure with desflurane 6%. This study shows that isoflurane, desflurane and sevoflurane are suitable for ostrich embryo immobilization, which is a prerequisite for motion-artifact free imaging. Application of isoflurane 6% and sevoflurane 8% is a) safe as no embryonal deaths occurred after exposure and b) effective as immobilization was observed for approx. 70 min after the end of narcotic
... 18,19 As for the ostrich (Struthio camelus), pigeon (Columba livia), Brandt cormorant (Urile penicillatus) and black stilt (kaki, Himantopus novaezelandiae), although trends for the development process have been roughly described, no staging system has been described and many of the characteristic development nodes were missed ( Figure 1). [20][21][22][23][24] Nevertheless, all of these developmental studies are of great significance for the comparative studies of birds, however, most of the studied species are concentrated are neognaths ( Figure 1). Embryonic stages of development for another representative species of cursorial birds (ratites), belonging to paleognath, such as the African ostrich, has not yet been defined. ...
... [30][31][32] In the area of development, with increased availability due to artificial breeding, the ostrich has recently become a popular model animal, with the development of its stomach, testis, testicular capsule and rete ducts being studied. [33][34][35] Although there have been a few studies on embryonic development in the ostrich, they have wide sampling intervals that result in a limited description of its embryonic stages, [20][21][22] and no stage system corresponding to the chicken HH system has yet been established. Thus, comparative studies between ostrich and chickens, or other birds, are limited, and key development stages may be missed. ...
... Previous studies have shown that embryonic development in the ostrich is similar to that seen in chicken and most other birds for early somite development. 10,22,40 Based on the chicken HH staging system, no obvious morphological differences were seen after stage 40, and only the beak length and the longest toe length were recorded, which is of little significance to the study of developmental biology. Therefore, limited by the number of available samples, we focused on the developmental period between stages 21 and 40, which contain the key stages for morphological differentiation between different bird species and includes the common stages of bird morphological development that are studied at the molecular level. ...
Background
The chicken has been a representative model organism to study embryonic development in birds, however important differences exist among this class of species. As a representative of one of oldest existing clades of birds, the African ostrich (Struthio camelus), has the largest body among birds, and has two toes. Our purpose is to establish the corresponding stages in ostrich embryo development that match the well‐established HH system of the chicken to facilitate comparative studies between the ostrich and other birds to better understand differences in development.
Results
Here we describe in detail the middle period of embryonic development using microscopic images and skeletal staining. We found that clear morphological differentiation between the ostrich and the chicken begins at stage 26. Bird limb cartilage first form in stage 25, while the development of the limb skeletons differs after stage 31. Calcification of limb skeletons in the chicken was completed faster. The first and second toes of the ostrich disappear at stages 36 and 38, respectively.
Conclusions
This study should greatly aid ostrich‐related developmental and morphological research and provide a reference for studying the development and evolution of avian limb skeletons, including molecular research. Questions that can now be addressed include studies into the fusion of tarsometatarsal skeleton, ossification, and digit loss.
... Artificial incubation of ostrich eggs usually takes 42 days until an ostrich embryo is fully developed and hatching occurs (Gefen & Ar, 2001). In chronological order blastogenesis, embryogenesis and foetal period describe embryonal development of eggs in general. ...
... Qualitative properties of embryonal stages in eggs have been investigated extensively and are usually described with a system introduced by Hamburger and Hamilton, defining "H&H" stages according to embryonal development steps (Hamburger & Hamilton, 1951, 1992. This system is based on post-mortem sections of regular chicken eggs (Gallus gallus domesticus), and it also applies-with few limitations-to ostrich development (Gefen & Ar, 2001;Brand et al., 2017). Chicken embryos usually hatch after 21 days and ostrich embryos after 42 days, which contributes to rather simple translation of development stages (Gefen & Ar, 2001). ...
... This system is based on post-mortem sections of regular chicken eggs (Gallus gallus domesticus), and it also applies-with few limitations-to ostrich development (Gefen & Ar, 2001;Brand et al., 2017). Chicken embryos usually hatch after 21 days and ostrich embryos after 42 days, which contributes to rather simple translation of development stages (Gefen & Ar, 2001). The embryonal structures of chicken eggs are too small to be depicted on regular scanners used in clinical routine with humans; therefore, they have been investigated using dedicated small animal imaging devices as micro-CT, -MRI, -SPECT and -PET (or the combination thereof) (Bain et al., 2007;Gebhardt et al., 2013;Heidrich et al., 2011;Klose et al., 2017;Kulesa et al., 2010;Wurbach et al., 2012). ...
In‐ovo imaging using ostrich eggs has been described as a potential alternative to common animal testing. This approach is independent from small animal imaging devices as ostrich eggs provide good image quality on computed tomography (CT), MRI or PET scanners used in clinical routine examinations. However, questions regarding physiological development and systematic evaluation of image quality are open. This study aims at describing physiological development of ostrich embryos on serial CT scans. One hundred eggs (63 fertilized and 37 non‐fertilized) were artificially incubated for 37 days. On developmental days (DD) 0, 10, 19, 22, 25, 28, 31, 34 and 37, CT scans were performed using a Siemens Biograph mCT40. Density of yolk, albumen and shell as well as volumes of air cell, egg content and egg shell were determined. In fertilized eggs, the size of different osseous structures was investigated. Detection of embryonal development was technically successful in 100%. Distinguishing of fertilized and non‐fertilized eggs is achieved as early as DD 22. After that, continuous development is depicted and osseous structures become visible on DD 25. Ostrich eggs might open the door for preclinical imaging studies if small animal imaging devices are not available. This study contributes to the implementation of ostrich eggs as an alternative to common animal testing.
... Thus, the incentive of this study was to investigate the ultrastructure of pre-meiotic germ cells and the organisation of meiotic prophase in ostrich germ cells. Considering the fact that the period of embryonic development in ostrich is twice longer than the chicken's embryonic development (42 days vs. 21 days), we chose specific days of development in order to register the most important developmental changes (Gefen & Amos, 2001;Kheirabadi et al., 2014). This report has documented the ultrastructural characteristics of ovarian germ cells during development of germ cell in ostrich embryo. ...
In this study, the ultrastructural development of germ cells in the ostrich embryo was analysed. The nuclear organisation and morphological characteristics of cytoplasm in the developing germ cells, on embryonic days 20, 26, and 36 and the day of hatching (5 samples from each stage) was analysed using transmission electron microscopy (TEM). Germ cells located in the cortex of left ovaries were identified by their large size and centrally located nucleus, with a conspicuous nucleolus. In these cells, the cytoplasm contained an abundance of mitochondria and free ribosomes. The structure of Balbiani body, a villous-like elevation in wide intercellular space and desmosome junction between two adjacent germ cells was also studied. The germ cells during embryonic development showed structural differences in both the nucleus and cytoplasm.
... The experiments involved fertilized eggs of the following animals: gecko (Paroedura picta; eggs were collected from adults maintained in the laboratory, incubated at 28 -298C, staged according to [13] (NR stage, which is equivalent to dpo in [13])); turtle (Pelodiscus sinensis; Daiwa Youshoku, Japan, embedded in wet sand and incubated at 308C, staged according to [14] (TK stage)); ostrich (Struthio camelus; Niseko Ostrich Farm and KO-COOP, Japan, incubated at 378C, staged according to [15] (GA stage)); quail (Coturnix japonica; Motoki Corporation, Japan; incubated at 38.58C, staged according to [16] (HH stage)) and chicken (Gallus gallus domesticus; wild-type, Iwaya Poultry Farm, Japan; homozygous and heterozygous limbless mutant, UC Davis Avian Science Facility, USA; incubated at 38.58C, staged according to [16] (HH stage)). ...
Understanding morphological evolution in dinosaurs from a mechanistic viewpoint requires the elucidation of the morphogenesis that gave rise to derived dinosaurian traits, such as the perforated acetabulum. In the current study, we used embryos of extant animals with ancestral- and dinosaur-type acetabula, namely, geckos and turtles (with unperforated acetabulum), and birds (with perforated acetabulum). We performed comparative and experimental analyses, focusing on inter-tissue interaction during embryogenesis, and found that the avian perforated acetabulum develops via a secondary loss of cartilaginous tissue in the acetabular region. This cartilage loss might be mediated by inter-tissue interaction with the hip interzone, a mesenchymal tissue that exists in the embryonic joint structure. Furthermore, the data indicate that avian pelvic anlagen is more susceptible to paracrine molecules, e.g. Wnt ligand, secreted by the hip interzone than ‘reptilian’ anlagen. We hypothesize that during the emergence of dinosaurs, the pelvic anlagen became susceptible to the Wnt ligand, which led to the loss of the cartilaginous tissue and to the perforation in the acetabular region. Thus, the current evolutionary-developmental biology study deepens our understanding of morphological evolution in dinosaurs and provides it with a novel perspective.
... Precise determination of the equivalent developmental stages in some other bird species is problematic, especially when the specificity in the later stages (as per Hamburger and Hamilton, 1951) cannot be successfully applied (Bartholemew and Goldstein, 1984;Ainsworth et al, 2010). Thus, many bird embryological descriptions do not use the Hamburger and Hamilton (1951) staging system, instead describing the specimens by incubation day (e.g., Fant, 1957;Padget and Ivey, 1960;Cooper and Batt, 1972;Maunder and Threlfall, 1972;Haycock and Threlfall, 1975;Desai and Malhotra, 1980;Mahoney and Threlfall, 1981;Bird et al., 1984;Bartholemew and Goldstein, 1984;Gefen and Ar, 2001). ...
... Extended morphological development (both differentiation and growth phases) has been reported for other birds with lengthened incubation times (Herbert, 1967, Gefen andAr, 2001;Nagai et al., 2011). In these cases, these morphological changes were reflected throughout development and are indicative of a decrease in developmental speed. ...
... In numerous birds, either all three (Herring gull: Haycock and Threlfall, 1975;Common guillemots: Mahoney and Threlfall, 1981), four (Duck: Koecke, 1958;Cotornix quail: Padgett and Ivey, 1960;Bob-White quail: Hendrickx and Hanzlik, 1965; Ad elie penguin: Herbert, 1967;Brown Pelican: Bartholemew and Goldstein, 1984), or five (Society Finch: Yamasaki and Tonosaki, 1988) toes are retained throughout the full developmental period. Toe loss has been described in three different bird species; both the ostrich (Gefen and Ar, 2001) and the chick (Hamburger and Hamilton, 1951) lose a single toe, second and fifth, respectively, whereas the Laysan Albatross in thus far the only bird species which initiates the development of five toes, and loses two toes (first and fifth) during development. Whether digit and toe loss is more common in bird lineages, but unreported, or whether this is a feature of an elongated development requires further analysis and examination of other birds with long incubation periods. ...
The Nasolacrimal Apparatus (NLA) is a feature common to many tetrapods, consisting of an orbital gland (Deep Anterior Orbital gland: DAOG aka Harderian gland), a nasal structure (Vomeronasal organ: VNO) and a connecting structure (Nasolacrimal Duct: NLD). There is variation in presence, relative development and ontogeny of each of these components between species. For example, in birds, the DAOG and NLD are well-developed in many species, but the VNO has not been documented in any adult bird. The embryogenesis of the NLA has only been described in chickens, a group of birds with a short incubation period. The objectives of this study were to describe the embryogenesis of the NLA in a bird with one of the longest incubation periods in an effort to determine whether 1) length of incubation period influences sequence and/or timing of NLA development and 2) whether the chicken is a suitable model for bird development. A series of embryos of the Laysan Albatross, a migratory sea bird whose incubation period averages 65 days, were processed for paraffin histology, serially sectioned and examined with special reference to the NLA. The embryogenesis of the NLA can be subdivided into three broad phases: 1) Origin (Stage 27–28); which includes inception of NLD as an epidermal, near vertical structure residing within the lacrimal lake of the lateral nasal wall. 2) Displacement (Stage 29–33): NLD detaches from the epidermal wall and shifts more deeply within the mesenchyme in the lateral nasal wall. This structure steadily elongates, approaching but not strictly attaching to the orbital and nasal regions. Lacrimal canaliculi form with the DAOG anlage opening just below the upper lacrimal canaliculus. 3) Development of ancillary features (Stages 34–39): The NLD continues to elongate and migrate laterally approximating its final position. Two features develop during this phase: 1) a VNO-like structure. This is a pair of small medial diverticula in the nasal septum, which, unlike a true VNO, this is not found in the floor of the nasal cavity and do not appear to have any sensory neurons. 2) Bony support for the NLA. NLD passes medial to the nasal/premaxilla bones (lateral to the nasal capsule), traverses the antorbital fenestra and passes lateral to the lacrimal bone, thereby connecting the orbital to the nasal region. This sequence of events in the Laysan Albatross is similar to those described in both the American Alligator and in humans, but unlike that described in the chicken. Though adult birds lack a VNO, the presence of a VNO-like structure in the developing Laysan Albatross, as in the developing crocodile, supports prior suggestions that it is a primitive characteristic which appears as a transitional embryonic structure. This would imply that a longer incubation period allows for the development of features, even if they are transitory, that are otherwise lost in species with shortened incubation period. Thus the chicken and the Laysan albatross, with their different incubation periods, show that there is a spectrum of bird embryology, and that a single bird (i.e., the chicken) should not be used as the sole model for Avian development.
... Precise determination of the equivalent developmental stages in some other bird species is problematic, especially when the specificity in the later stages (as per Hamburger and Hamilton, 1951) cannot be successfully applied (Bartholemew and Goldstein, 1984;Ainsworth et al, 2010). Thus, many bird embryological descriptions do not use the Hamburger and Hamilton (1951) staging system, instead describing the specimens by incubation day (e.g., Fant, 1957;Padget and Ivey, 1960;Cooper and Batt, 1972;Maunder and Threlfall, 1972;Haycock and Threlfall, 1975;Desai and Malhotra, 1980;Mahoney and Threlfall, 1981;Bird et al., 1984;Bartholemew and Goldstein, 1984;Gefen and Ar, 2001). ...
... Extended morphological development (both differentiation and growth phases) has been reported for other birds with lengthened incubation times (Herbert, 1967, Gefen andAr, 2001;Nagai et al., 2011). In these cases, these morphological changes were reflected throughout development and are indicative of a decrease in developmental speed. ...
... In numerous birds, either all three (Herring gull: Haycock and Threlfall, 1975;Common guillemots: Mahoney and Threlfall, 1981), four (Duck: Koecke, 1958;Cotornix quail: Padgett and Ivey, 1960;Bob-White quail: Hendrickx and Hanzlik, 1965; Ad elie penguin: Herbert, 1967;Brown Pelican: Bartholemew and Goldstein, 1984), or five (Society Finch: Yamasaki and Tonosaki, 1988) toes are retained throughout the full developmental period. Toe loss has been described in three different bird species; both the ostrich (Gefen and Ar, 2001) and the chick (Hamburger and Hamilton, 1951) lose a single toe, second and fifth, respectively, whereas the Laysan Albatross in thus far the only bird species which initiates the development of five toes, and loses two toes (first and fifth) during development. Whether digit and toe loss is more common in bird lineages, but unreported, or whether this is a feature of an elongated development requires further analysis and examination of other birds with long incubation periods. ...
Bird incubation is subdivided into two phases: differentiation (embryonic phase) and growth (fetal phase). Most birds have a relatively short incubation period (20-30 days) with the phase transition occurring midway through the incubation period. The Laysan albatross (Phoebastris immutabilis) is a large pelagic bird with a long incubation period. The purpose of this study was to document the differentiation phase with the aim of ascertaining the impact of a lengthened incubation on embryonic development. Eighty-two previously collected albatross embryos were examined, measured, and staged. The albatross was found to develop more slowly than smaller birds, with a rate similar to other long-incubating birds. Legs and wings grow at similar rates but exhibit variation in growth among their anatomical components. While the albatross embryos shared some morphological stages with chickens, they were more similar to ducks and pelicans. Special features of the albatross not shared with the Gallianserae (chickens and ducks) included an alligator-like curved tail, narial tubes, and a cloacal bulge. Further examination of other larger pelagic birds with long incubation periods are needed to determine the uniqueness of the Laysan albatross embryonic development. Although much embryonic phase growth was documented in the postnatal period, little is known about the later, fetal phase in Laysan albatross. Future studies should involve examination of later (post day 32) fetuses. J. Morphol., 2016. © 2016 Wiley Periodicals, Inc.
... External morphological characteristics of embryo development have been studied in flightless birds such as the ostrich (Gefen and Ar, 2001) and emu (Nagai et al., 2011), with incubation periods of 38-40 and 50-51 days, respectively. They have also been studied in birds with shorter incubation periods, such as the American falcon (Bird et al., 1984;Pisenti et al., 2001), pheasant (Labisky and Opsahif, 1958), bob-white (Hendrickx and Hanzlik, 1965), Japanese quail (Ainsworth et al., 2010), pigeon (Olea and Sandoval, 2012), zebra finch (Murray et al., 2013). ...
... The common morphological characteristics observed between 5 and 7 days incubation were also reported by Labisky and Opsahif (1958) in the pheasant at 5 and 6 days, in the falcon at 6 and 9 days (Bird et al., 1984) and at 2.5 days in the pigeon (Olea and Sandoval, 2012). The maximum flexion of the greater rhea embryos can be considered precocious when compared with the ostrich embryo described at 8 days (Gefen and Ar, 2001). At 5 days the limb buds of the greater rhea embryo were similar to those of 3-day-old Japanese quail (Ainsworth et al., 2010), in the hen between 3 and 4 days (Hamburger and Hamilton, 1992;Saunders, 1998), and were distinctly longer in the present research at 6 days and with rounded extremities at 7 days. ...
... Although the nictitating membrane appeared in both the greater rhea and the bob-white (Hendrickx and Hanzlik, 1965), at 8 days, proportionally, considering the incubation time of the species, the appearance of this structure was earlier in the greater rhea development and in relation to the ostrich (Gefen and Ar, 2001), that appeared at 14 days. This fact was also observed for the eyelid that, in the greater rhea appeared at 8 days and in the ostrich (Gefen and Ar, 2001) only at 14 days, and was described at 8.5 days in the pigeon (Olea and Sandoval, 2012) and 5 days in the Japanese quail (Ramteke et al., 2013). ...
... In comparing the development of the ostrich and the chick which is well known to, it is clear that according to the difference in incubation periods viz., 42 days for the ostrich and 21 for the chick, the degree of development of the gonads at the time of incubation is about twice (Gefen 2001). In chicken on the 6th and 7th days of incubation, the first histological outlines of gonadal sex differentiation are detectable; the left ovary in females shows secondary sex cords in the form of groups of somatic cells including germ cells; the right ovary has a thinner germinal epithelium, and no secondary sex cords (16,22). ...
... Scale bar 10 μm. GE germinal epithelium, Gc germ cells, M medulla, v blood vessels, L lacunar channels, and E erythrocyte ostrich, while the outer cortical layer starts to proliferate in ovaries, and the left ovary showed a cortex and medulla This may be associated with ostrich's longer incubation period; in other words, ostrich's embryonic development is about twice that of the chicken (Gefen 2001), and so the gonad differentiation also began later than in chicken; However, there was delay in gonad differentiation in ostrich compared to chicken. ...
The aim of this study was to investigate the histological development of right and left ovaries in ostrich embryo. The research was carried out on the ovaries of 20-, 26-, 30-, and36-day-old embryos. At first, anatomical observation was done, and then 5 μm sections of ovaries were stained by hematoxylin and eosin, periodic acid Schiff, and Masson’s trichrome staining methods. Some ovaries embedded in Epon and 1 μm thickness sections were stained with toluidine blue and examined using regular optical microscopy. The results showed ovaries had an unequal growth resulting into a larger left ovary with obvious cortex and medulla. Cortex consisted of germinal cells and germinal epithelium along with somatic cells. At 26 days, the left ovarian cortex was developed with increasing the size of secondary sex cords and numerous germ cells. At more advanced stages of development, germ cells grew in size and contained more granules in the cytoplasm. In the right ovary cortex, there was none visible, and germinal epithelium had a thin layer. Lacunar channels, blood vessels, and interstitial cells along with germ cells were present in the medulla of both ovaries. The medullary germ cells were observed as solitary cells or group of several cells. In general, we demonstrate the histological changes in the left and right ovaries of ostrich from 20- to 36-day-old embryos. In addition, this work is the first study that provides histological evidence for the normal structure of ovaries and suggests the time of onset of meiosis in the ostrich embryo
... By using egg breakout, it was established that early embryonic mortalities in some turkey hatcheries can be a major problem (Sellier et al., 2006). Embryonic development, as described by Hamilton and Hamburger (1951), is a series of consecutive rather than chronological stages, which accounts for the variation between embryos of the same chronological age (Gefen and Ar, 2001). The latter authors suggested that this variation might result from factors such as differences in physical conditions of incubators, the embryonic stage when incubation commences and genetic variation among embryos. ...
... The pear-shaped form of the blastoderm at 48 h of incubation in our study resembled the late primitive steak phase (stage 4-5; 18-22 h) in the chicken (Hamburger and Hamilton, 1951) and stage 17 in the duck (Dupuy et al., 2002). The present results showed the occurrence of blood islands within the AV by 72 h of incubation and a wide network of blood vessels surrounded the developing embryo at 96 h of incubation, which differ from Gefen and Ar (2001), who only observed blood islands in ostrich eggs from 96 h of incubation. After 72 h of incubation the ostrich embryo is consistent with stage HH8 (26-29 h) for chickens (Hamburger and Hamilton, 1951) and stage 21 for ducks (Dupuy et al., 2002). ...
... After 72 h of incubation the ostrich embryo is consistent with stage HH8 (26-29 h) for chickens (Hamburger and Hamilton, 1951) and stage 21 for ducks (Dupuy et al., 2002). The mean length (11.9 mm) of the AV at 96 h of incubation in the current study corresponded with the 10 mm reported by Gefen and Ar (2001). The rotation of the embryo at 120 h of incubation corresponded with stage HH16-17 (51-64 h) of the chicken (Hamburger and Hamilton, 1951). ...
Abstract 1. Early development of ostrich embryos was investigated in relation to time of egg collection
and genotype.
2. A total of 321 ostrich eggs were collected during the 2008 and 2009 breeding seasons and the
development of the embryo for up to the first 168 h of incubation was described and analysed. A sample
of the incubated eggs was weighed and opened daily to investigate developmental changes.
3. In fresh eggs, the blastoderm contained a round, translucent dark area pellucida (AP) in the centre,
with a surrounding thin white ring, likely to be the beginning of the area opaca (AO). Fresh eggs were
considered infertile if the blastoderm was absent and instead numerous white droplets were present
surrounded by vacuoles.
4. The average blastoderm area of a fresh fertile egg was 15.8 mm2, increasing to 143.3 mm2 after 2 d of
incubation. By 72 h of incubation the area vasculosa (AV) was discernible in the posterior half of the
blastoderm.
5. At 48 h of incubation the blastoderm area in eggs from the South African Black genotype
(SAB) × Zimbabwean Blue genotype (ZB) crosses (104.5 ± 18.6 mm2) was lower than the pure SAB
(141.0 ± 10.5 mm2), ZB (161.7 ± 13.5 mm2) and ZB × SAB crosses (166.1 ± 14.2 mm2).
6. Embryo length was 5.01 mm after 72 h of incubation and 14.5 mm after 168 h of incubation. At 168 h of
incubation AV lengths for both ZB × SAB (53.2 mm) and SAB × ZB crosses (54.1 mm) were longer than in
embryos from the pure breeds.
7. Results from this study can be put to practical use when determining whether eggs are infertile or
fertile and also in investigating the age of early embryonic mortalities.
