Chicken schedule involving extra egg? (7)

I believe the answer is:

rooster

I'm a little stuck... Click here to teach me more about this clue!

'chicken' is the definition.
(I know that rooster is a type of chicken)

'schedule involving extra egg?' is the wordplay.
'schedule' becomes 'roster' (I've seen this before).
'involving' indicates putting letters inside.
'extra egg?' becomes 'o' (an 'o' resembles an egg. I am not sure about the 'extra' bit.).
'roster' going around 'o' is 'ROOSTER'.

Can you help me to learn more?

(Other definitions for rooster that I've seen before include "Cockerel (mainly US)" , "So retro (anag.)" , "Toreros (anag.)" , "Adult male domestic fowl" , "Male domestic fowl in USA" .)

I've seen this clue in The Independent.

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