Caulfield Cup winner Southern Speed has been retired after an uneasy spring of mixed form and injury.

Trainer Leon McDonald said the decision came after a thorough assessment of the damage to the mare's nearside suspensory ligament that caused her to miss the Melbourne Cup.

The daughter of American stallion Southern Image and the Zabeel mare Golden Eagle will have an easy time until next spring's breeding season.

Southern Speed won seven races and $2.8 million during a career in which she showed versatility and courage winning in Group company from 1400m to 2400m, her greatest success coming in last year's Caulfield Cup.

Connections of Americain have also announced preliminary breeding plans for the 2010 Melbourne Cup winner with his first stud duties to be performed in America.

Part-owner Gerry Ryan said a "large Kentucky farm" had shown interest in the horse and a deal was expected to be sealed in the next few weeks.

Americain was bred in the US where his sire Dynaformer stood at the famous Three Chimneys Farm until his death earlier this year.

Ryan said Americain would shuttle between the US and Australia with Victorian and NSW studs already competing for his services.