fullblood simmental x. commercial black angus cow = black heifer calf, 50% F1 simangus
fullblood simmental x. F1 simangus heifer = black heifer, 75% F2 sim-simangus
fullblood simmental x. F2 sim-simangus = black heifer, 87.5% F3 sim-sim-simangus
fullblood simmental x. F3 sim-sim-simangus = black calf, 93.75% F4 sim-sim-sim-simangus
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Now, if someone replaces the "fullblood simmental" with a 93.75% F4 sim-sim-sim-simangus, the percentage of actual simmental blood in the resulting F4 would be only 87.9% simmental blood ... even though the simmental association says it's a purebred and would be worth 100% in future breed-up scenarios.
Pretending for a second, this 87.9% 'purebred' simmental is used in the 3rd round of breed up, that F4 would only have only 82.4% simmental blood.
This degredation of hybrid vigor only increases each time something other than a fullblood is used when getting to a 'purebred' of almost every breed that allows breed-up programs.
Commercial cattleman beware.
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So, back to the original question...
The black probably came from black angus; possibly galloway.
The hereford marks came from a hereford.
And, if someone is marketing them as gelbvieh then presumably there is gelbvieh is in there somewhere.
So, yes, they're selling three-way-cross bulls.