By terminal do you mean that all the F1 males go to beef, but the females (after sort) can be retained as F1 replacements? (I always thought terminal meant no animals would be retained) Then, after another cross, all the F2 animals go to beef?
I mean the most efficient production model is to breed F1 cows (angus/ shorthorn) to a bull of a third breed (charolais, for example)
As an example. One has a good enough group of Shorthorn cows (not perfect, but to the point where good enough means pretty all around good for the environment). These cows are half sisters. They are crossed to another breed (say they are crossed to Red Angus) The steers are sold and some F1 females are retained or sold as replacements.
Red Angus would be a good choice (?) because both breeds are compatible and considered maternal. So the F1 females will be a sort of blend instead if a volatile union of opposites.
Yes, though all breeds 'are compatible.' You would likely experience more variation creating, for example, an F1 Gelbvieh/Shorthorn cow, but with the inputs to this cross being more unrelated, you would experience a greater degree of maternal heterosis than you would by creating the F1 from two more closely related (shorthorn and red angus) british breeds. This is where/why many choose to forego a little heterosis for the sake of consistency
Now the F1 females are crossed to a third breed (say Charolais) and all the progeny are sold as beef.
But to stay true to the foundation Shorthorn cows for future replacements, seems like the best you can do is to get back to 75% Shorthorn, even if that 75% is line bred.
I'm confused a little here. The foundation shorthorn cows are 100% shorthorn. I don't follow you w/ the 75%? I would never breed an f1 back to one of her foundation breeds. This results in what's known as "regression" which is the opposite of heterosis.
At what point does the percentage of a line become more important than the percentage of a breed?
I still think there is some folklore out there about which way crosses work better. Although it cannot be proven, and may seem irrational, I think most information handed down by farmers about livestock is rooted in truth.