Do physical and chemical characteristics of Greater Rhea eggs change throughout the laying season

LABAQUE M.C.; MAESTRI D.M.; HOYOS L.; MARTELLA M.B.; NAVARRO J.L.

Madrid (España)

Congreso; 3rd Internacional Ratite Science Symposium; 2005

The quality of eggs is important for the correct development of the embryo. Physical and chemical characteristics of Greater and Lesser rhea eggs have been described in previous studies. However, whether these properties change throughout the laying season and their effects on hatchability remain unknown. To explore this question, all the eggs (n=252) laid by 12 captive Greater rhea females on a fixed diet were collected from September 2000 to January 2001 to determine their physical and chemical characteristics and hatching success. Eggs of each female were identified and classified into four periods according to their laying date. The egg weight, length, width and volume were measured, and up to four eggs of each female were randomly selected from each period to determine the specific weight, proportions of yolk, albumen and shell (based on entire egg weight), protein and lipid contents, and fatty acid composition. The remaining eggs (n = 180) were artificially incubated and monitored until hatching. Physical and chemical data were subjected to a Friedman repeated measure ANOVA, with period as treatments and females as blocks, and hatchability to a Chi-squared contingency table test. The specific weight of eggs was lowest in September. In contrast, yolk protein, stearic, and almost all the unsaturated fatty acids (linoleic, linolenic, arachidonic) tended to increase as the laying season progressed, particularly in the last period (December and January), while total yolk lipid content, oleic and palmitoleic acids showed an opposite trend. No significant variations were detected in other physical characteristics or albumen protein content. Differences observed in egg composition seem to be not high enough to affect hatchability, since it was invariant throughout the laying season (overall: 69%). Quality of eggs may also be related to individual females traits (genetic or physiological characteristics, age, weight, etc.) or to environmental conditions, and these relationships will be investigated in future studies. Key words: ratites, eggs, fatty acids, physical characteristics, chemical characteristics, hatchability.