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Araucanasandbrown-eggbreedsmakeboth
blueandbrownpigmentsandthusgreen
shells.
Thecompletedeggisexpelledbluntend
firstabout25hoursafterleavingtheovary.
Astheeggcoolsdownfromthehen’shigh
bodytemperature(106ºF/41ºC),itscontents
shrinkslightly.Thiscontractionpullsthe
innershellmembraneawayfromitsouter
partneratthebluntendandtherebyformsthe
airspace,whosesizeisanindicatorofegg
freshness(p.81).
TheYolk
Theyolkaccountsforjustoverathirdofa
shelledegg’sweight,anditsbiological
purposeisalmostexclusivelynutritive.It
carriesthree-quartersofthecaloriesandmost
oftheiron,thiamin,andvitaminAoftheegg
asawhole.Theyolk’syellowcolorcomesnot
fromthevitamin-Aprecursorbeta-carotene,
theorangepigmentincarrotsandotherplant
foods,butfromplantpigmentscalled
xanthophylls(p.267),whichthehenobtains
mainlyfromalfalfaandcornfeeds.Producers
maysupplementthefeedswithmarigold
petalsandotheradditivestodeepenthecolor.
Duckyolksowetheirdeeperorangecolor
bothtobeta-caroteneandtothereddish