how large are they?
You didn't state the diameter, only length as 8 to 9 ft.
Hickory is a great wood to make furniture with. Chests and cases etc also. BUT you will need to have it milled into 4/4 thick slabs. If the logs are 12" or large in MAY be worth getting them milled ... who knows, only a saw mill operator.
I would only use pressure treated 6 x 6 posts for your cattle fence, and depending on the run maybe some 4 x 4 's in between? Any posts I have ever put into contact with soil I painted them in used motor oil or sprayed them with automotive undercoat. The best soil is well drained sand and gravel. A highly organic black soil that retains water will be an issue.
So, there are some variables here, but using PT posts will solve most of them. I don't pour concrete around mine, but I do pack the soil in with a jack hammer or a 2 x 4 about every 4" down. This makes the post very rigid. For gate posts I use 6 x 8 x 8ft long and brace them diagonally when possible.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)