Frankie's post is most correct. The F1 is the first filial relationship in a cross.
When a third or fourth breed is introduced the designation becomes F2, or F3.
Maximum heterosis is achieved when a true F1 is bred to a third breed. The resultant offspring should usually be sold and not used for further breeding, but by going back to one of the first 2 components of the original F1, a decent result can be obtained.
Moving strictly into cattle, the problem that has occured in North America is that most ranchers never learned proper crossbreeding techniques. They move from one breed to the next, sometimes even breeding multiple breeds at the same time. When the 4th breed is introduced, heterosis is actually reduced, making straightbred or F1's superior in most every trait.
Finally after years of mongrel cattle the nations cowherd is being cleaned up by using one breed more than others, Angus.
Why Angus? Angus is a maternal breed that has good feed conversion and excellent carcass traits, along with a vast gene pool and accurate epd's. Once ranches have used Angus for 2 or 3 generations, they can embark on limited crossbreeding again to use heterosis to their advantage.
An alternative to this approach would be to purchase straightbred heifers or true F1 crosses from herds that never got carried away with multiple crosses.
Jason Trowbridge Southern Angus Farms Alberta Canada
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