Abstract
A total of 2160 images of candled, incubated ostrich eggs were digitized to determine the percentage of egg volume occupied by the air cell at different stages of incubation. The air cell on average occupied 2.5% of the volume of fresh eggs. For eggs that hatched successfully, this volume increased to an average of 24.4% at 41 days of incubation, just prior to hatching. Air cell volume at 29 days of incubation for infertile eggs (19.3%) was significantly higher when compared to dead-in-shell (DIS) eggs (14.3%) and eggs that hatched (13.8%). There was a significantly larger air cell volume in eggs that hatched normally compared with DIS eggs at 41 days of incubation (28.3% vs. 21.7%, respectively). No differences in air cell volume were observed up to day 17 of incubation for eggs that hatched normally between eggs that exhibited high, average or low rates of water loss, but from 20 days of incubation the air cell volume was significantly larger for high weight loss eggs. However, for the DIS eggs, air cell volume was consistently larger in eggs that exhibited high rates of water loss. Air cell volume was largely independent of adult strain (SA Black or Zimbabwean Blue) or whether chicks were assisted to hatch. Although some subtle differences in air cell size were detected between hatched and DIS chicks during this study, it is unlikely to find useful application in the broader industry.
Highlights
Ostrich farming is a major agricultural enterprise in South Africa
The average weight of the 120 eggs used in this study was 1 389 ± 112 g, with a coefficient of variation (CV) of 8.11% (Table 1)
Water loss ranged from 4.6% to 13.0% of fresh egg weight at day 21 of incubation, and 7.4% to 20.0% at day 35 of incubation, with higher CVs of 23.9% and 24.1%, respectively
Summary
The usual commercial practice is to keep breeding birds in large flocks or as pairs in small enclosures. Eggs are collected daily, and incubated artificially. With hatching rates of only 50% - 60% (Brown et al, 1996; Deeming & Ar, 1999; Van Schalkwyk, 2000), the success rate of artificially incubated ostrich eggs is low when compared with the hatching success of commercially reared chickens (90% - 95%), turkeys (75% 77%) and ducks (65% - 82%) (Hodgetts, 1990; Deeming, 1999). The low hatching success represents a considerable loss of production, and is a cause of concern in the local industry. Poor understanding of the pattern of embryonic development in ostriches may contribute to the poor hatching results reported previously
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