"At first I Googled it and it looked like it was the smallest egg in the world, but I've gone further into the archives and there's a smaller one by 2mm. So maybe this is the smallest in Australasia."
Earlier this year, British man Keith Bacon made headlines with an egg laid by one of his chickens that measured 28mm.
In 2011, the World Record Academy recorded the smallest chicken egg, from Charleston, measuring 21mm.
"I'd say we're number two, by the looks of it," Mr Horne said. "It's about a 10c piece, maybe a little bit bigger."
Mr Horne said they did not yet know what they would do with the egg.
They were considering approaching a chicken processing company to offer the egg as a showroom piece.
Mr Horne said his research indicated the egg probably did not have a yolk.
Tiny, yolkless eggs were sometimes known as witch eggs, fairy eggs or cock eggs.
These were often the result of a hen that had not lain an egg for some time and was getting back into its reproductive cycle.
"I just thought it looked like a little scorched almond," Mr Horne said. "It's a perfect little miniature egg."
Dr Liza Schneider, director of Holistic Vets, said it was not unusual for a chicken to lay an egg considerably smaller than normal as "there's always the opportunity for diversity".
However, she had not heard of a such a tiny chicken egg.
"Sometimes aberration with egg size or shape can be due to an underlying disease or illness, but in all likelihood this is one of those flukes," Dr Schneider said.
"What a shame he missed out by 2mm."
The Guinness World Records did not have a smallest chicken egg category but the smallest egg laid by any bird is that of the vervain hummingbird of Jamaica.
Two specimens measuring less than 10mm in length weighed 0.365g and 0.375g.
