Has anyone ever tried this? My understanding is it is a long process, but it can be done as follows;
Use a fully polled bull (homozygous polled) on a horned cow. All the offspring will be half-polled (heterozygous polled). 3rd row in Pic.
On the heifers from above, use another fully polled bull. 4th row in Pic. 1/2 offspring will be fully-polled and 1/2 will be half-polled.
Thinking of using a few polled Limousin straws I got recently. ICBF can test for the Polledness. Should have a fully polled Limousin bull in 10 years time.