<p/>White Plymouth Rock pullets selected for a high 8-week bodyweight have an unsatisfactory production of hatching eggs, but this is not the only problem. In addition a great proportion of ovulated yolks are lost for the formation of normal eggs, because they are laid in abnormal eggs. In a study on the relationship between yolk production and egg formation, abnormal eggs were found to be laid when ovulation rate exceeded the limit of one ovulation per egg formation period.<p/>Research on the genetic background showed that laying of double-yolked eggs, of two eggs a day, and of normal eggs only is genetically controlled to a large extent. Correlations were calculated between these laying traits and 8-week bodyweight, but those estimates did not provide a conclusive answer.<p/>Economically, first eggs of a pair have also to be seen as abnormal, because they proved almost unhatchable.<p/>With the help of the sex-linked dwarfing gene <em>dw</em> , it was shown that a reduction of yolk production in the ovary can result in an increase in normal egg laying in hens whose ovulation rate is too high. There seems therefore to be the relationship between total yolk production and the laying of abnormal or normal eggs.
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