Conversation so far:
When was retirement?
On November 17, 2010, Zenyatta was slated to be retired.
Was she injured?
CANNOTANSWER.
Did she retire at that time?
On February 23, 2011, she traveled by van to Darley Stud, where she was bred to Bernardini.
Are there any other interesting aspects about this article?
Zenyatta later give birth to a dark bay colt, eventually named Cozmic One, on March 8, 2012.
Did her colt go on to be a racing horde as well?
Cozmic One had two starts in 2015 and performed poorly at the track.
He has since been retired.
Who was her trainer?
CANNOTANSWER.
What other things happened during her retirement?
She delivered a chestnut colt, Ziconic, on April 1, 2013, her 9th birthday.
Did that colt go on to race as well?
Ziconic began his racing career in 2016, and, like his dam, demonstrates a last-to-first running style.
Did she have any other colts?
She delivered a dark bay filly, nicknamed "Z Princess," on Easter, April 20, 2014.
Did Z Princess also race?
The filly was euthanized as a weanling on October 28, 2014.

Question: Why did that happen?
Self-contained rewrite: Why did euthanized happen?