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Studies on egg shell pigmentation in the domestic fowl Gallus Domesticus

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LangMR_1989redux.pdf (21.07Mb)
Date
1989
Author
Lang, Malcolm Robert
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Abstract
 
 
The results presented in this thesis confirm that in brown eggs laid by the domestic hen the intensity of colour depends on the amount of protoporphyrin-IX in the egg shell. This pigment which constitutes about 42% of shell porphyrin, is concentrated in the cuticle, the thin proteinaceous layer which covers the shell.. Although the calcareous shell also contains pigment, its concentration, due to the larger mass, is vastly reduced in comparison to the cuticle, and therefore its contribution to the depth of colour is negligible. For this reason, the cuticle was used in this study to indicate the degree of shell colour intensity.
 
Variability in shell colour between eggs laid by individual hens is extremely large. In addition, in eggs from most hens, there is a decrease in shell colour as the laying cycle progresses. The loss of colour is attributed to a reduction in porphyrin content of the egg shell which is expressed in the cuticle. Overall, the lack of persistency in colour appears to be a less serious problem than was previously supposed, but it may still merit consideration in breeding programmes for dark shell colour. Furthermore, it was observed that darkly coloured eggs contained more shell than lighter ones, and it is suggested that selection for dark shells may be of practical value when wishing to improve shell strength.
 
While the cuticle was deposited on the shell at an even rate during the final stages of shell formation, within the shell gland pouch, this is not so for the pigment associated with it. By 3 hours before oviposition, 77% of the cuticle has been formed. Pigmentation, on the other hand is slow up to this point, after which time around 81% is added to the cuticle during the final 3 hours prior to oviposition. During this time, the depletion of shell gland tissue porphyrin corresponds to the uptake of porphyrin by the cuticle.
 
Oral administration of a porphyrin-inhibiting drug, Nicarbazin, reduced egg shell porphyrin content by more than 75%. The loss of pigment more closely corresponds to the magnitude in the reduction in shell gland tissue porphyrin, during treatment, than to the porphyrin content in the blood.
 
Finally, the biochemical processes of egg shell pigmentation and this relationship with cuticle formation are discussed.
 
URI
http://hdl.handle.net/1842/28400
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  • Biological Sciences thesis and dissertation collection

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