Artikel Factors related to shell deaths during artificial incubation of ostrich eggs

INTRODUCTION Artificial incubation has become an essential part of any commercial poultry enterprise. Ideally, every fertile egg should produce a healthy hatchling. In reality this situation is never achieved in a commercial hatchery. Despite substantial advances in incubator design and incubation techniques since the ostrich industry in South Africa began in the 1800s, problems with embryonic mortality during artificial incubation is still one of the main constraints to the development of the ostrich industry world-wide. Optimum incubator temperature used in automatic incubators is normally defined as that required to achieve maximum hatchability. The physiological requirements of the developing ostrich embryo are met by the control of temperature, humidity, gaseous environment and the turning of eggs. Although hatchability of artificially incubated ostrich eggs can reach 80 %, it is typically between 30 % to approximately 60 %. Deeming and Ar have reported hatchability of fertile eggs as low as 11 % in extreme situations. Shell-deaths thus contribute to a large extent to the low hatching rates in the ostrich industry. Embryonic mortality in ostrich eggs usually occurs either early or late in the incubation period, with relative few deaths in mid-term. The age of the female appears to be one of many factors influencing the number of eggs produced as well as hatchability. Females start egg production at an age of 2–2.5 years and peak egg and chick production are achieved at 8–9 years of age. This peak is followed with a general decline in reproductive performance at greater ages, which was more pronounced for chick production than for egg production. Ostrich females have a longer economic life compared with the other poultry species, therefore making it difficult to compare ostrich breeds with the small domestic poultry species traditionally used for egg production. In both broiler breeders and quail, young females have a higher proportion of early embryonic deaths than mature females. For ostriches the opposite seems to be true in the sense that embryonic survival decreases over successive laying seasons. Ostriches are generally regarded as seasonal breeders, with the commencement of the breeding season coinciding with an increase in photoperiod. According to Lambrechts, peak production for ostriches in the southern hemisphere occurs between winter (July) and summer (January). Genetic make-up is one of the factors influencing the performance of individuals and by selecting for certain traits, genetic improvement may be achieved. Egg quality is also reported to have significant genetic components. Fertility in turkeys is influenced genetically, with strain and variety differences that are apparent. Pre-incubation storage leads to morphological changes in the blastoderm and to a lower growth rate of the embryo in small domestic poultry. Albumen quality is compromised by prolonged storage time. A proportionate increase in early embryonic mortality occurs with an increased storage time of duck and quail eggs. This coincides with results of Deeming and Ar, reporting a lower hatchability in ostrich eggs that could be attributed to an increase in early mortalities for eggs stored between 12 and 14 days. Ar and Gefen, Badley, Sahan et al. and Hassan et al. also reported an increase in early embryonic mortalities for eggs stored for extended periods, up to 10 days and longer. The main objective of the present study was to investigate non-infectious factors that potentially influence embryonic