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Abstract
1. — Changes in egg weight and egg‐shell porosity with flock age and season are presented for domestic duck flocks in their first laying cycle.
2. — The first eggs laid are of low weight and shell porosity but generally by the fifth week of lay both characteristics have increased to the values found in the mature flock.
3. —For mature flocks porosity decreases in the summer and the consequences of this are considered in relation to the observed decrease in hatch‐ability at this time.