Synopsis
Six blocks of data are analysed: British Egg Marketing Board (BEMB) data on second quality eggs‐in‐shell in packing station throughput; shell thickness and colour data on 1,440 eggs sampled in 4 packing stations; crack incidence data on 162,480 individually recorded eggs from a two‐strain experimental flock kept in battery cages; similar data on 34,611 eggs from another experimental flock; shell thickness, volume and shape data on 76 eggs from 19 pairs of hens, one of each pair with a high and one with a low shell‐crack record; and BEMB data on the prevalence of battery and deep‐litter husbandry. Conclusions reached are:
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Over the last decade there has been a rise in the incidence of packing‐station egg downgrading in the United Kingdom; it is assumed to have been due largely to a rise in the incidence of cracked shells.
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The rise in crack incidence was probably not due primarily to deterioration in shell strength associated with high production rates or white shell colour; such associations were looked for but not found.
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It was probably due primarily to an increase in “ environmental insults “ to packing‐station eggs accompanying the spread of deep‐litter and battery husbandry; a close association was found between their incidence and that of downgrading.
Implications for cage designers, breeders, egg producers and research workers are discussed.