An F1 cross is used when, 2 different breeds are mixed.
Example, a dutch native horse with an TB result a riding horse.
The F1 termology is not used by mixing several bloodlines within one breed.
Thanks for the clarification. I recall seeing the designation F1 and like prfsue, I connected it with Louis' imaginative designations.
Simply, from Basic Genetics 101, hybrid vigor is not a consideration when two exact breed pairs are mated.
It appears that Whirlaway was attempting a "sympathetic seance" with Louis.