Lesley Reith, from Oxton in Merseyside, UK was shocked when she discovered the spherical egg in the nest box.
Reith was about to make an omelet with it before a friend persuaded her to sell it online.
Bidders scrambled to buy the natural treasure in the 10- day auction, which she said was "egg-cellent news" for her chosen dog charity, 'BBC News' reported.
"It was really strange. I used to have 50 chickens at my allotment and I have never seen one before. I don't think I will ever see one again - I think it is once in a lifetime," she said.
The money raised by the auction will go to a dog charity.
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