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Yolk Sac Retention in the Ostrich (Struthio camelus): Histopathologic, Anatomic, and Physiologic Considerations

Abstract Yolk sac retention or the failure to absorb yolk is a common problem in recently hatched ostrich chicks (Struthio camelus) and is one of the major causes of mortality in the first 2 weeks after hatching. In a study of 80 yolk sacs from dead-in-shell (DIS) eggs (n = 24) and ostrich chicks up to 3 weeks after hatching (n = 56), several aspects were considered. A predictive curve for normal growth and yolk absorption was calculated, a histologic study of “normal” and “retained yolk” sacs was conducted, and a microbiological evaluation of yolk sacs and the chicks was performed. Findings were discussed in comparison to comparable data for poultry and in relation to possible causes of yolk sac retention. At necropsy, the diagnosis of retained yolk sac was made 13 times. No differences were observed by histopathologic examination between chicks with yolk sac retention and normal chicks. When the predictive curve was compared with direct observations at necropsy, the direct method had a sensitivity and specificity of 52% and 93%, respectively. Using the predictive curve, 19 yolk sacs were considered to be retained. Bacterial growth was found in the yolk of 42% of the DIS chicks, in 26% of the normal chicks, and in 22% of chicks with retained yolk sacs. In most cases, the same organism was also cultured from the liver of the chick. The bacterium most commonly isolated was Escherichia coli. Omphalitis could not be correlated with any of the isolates.