Mac Swiney, inbred 2x3 to Galileo, is out of the unraced Halla Na Saoire (Teofilo). She is a full sister to Light Heavy, winner of the Gr.2 Derrinstown Stud Derby Trial and the Gr.3 Ballysax S. and third in the Gr.1 Irish Derby, and a half-sister to Halla Siamsa (Montjeu), who produced the Gr.1 Dewhurst S. winner Parish Hall and Hall of Fame, third in the Gr.2 Futurity S., both by Teofilo.

Second dam Siamsa (Quest).

Third dam Amoura (Northfields) is also the ancestress of An Ghalanta (Holy Roman Emperor), winner of the Listed Curragh S. and third in the Gr.3 Round Tower S. An Ghalanta is the dam of Time Scale (Charm Spirit), winner of the Listed Empress S., and Bletchley (Makfi), second in the Gr.2 Nassau S. and the Gr.3 Albany S.

Halla Na Saoire has an unraced two-year-old colt by Vocalised named Quavering.