Trample ability without a slam attack

[Michael Grate]

I was looking at the War Bull and as part of its 4th level advancement it gains Trample special attack.

Trample wrote:

Targets of a trample take an amount of damage equal to the trampling creature’s slam damage + 1-1/2 times its Str modifier.

but the War Bull doesn't have a slam attack, just a Gore. It also doesn't give a damage indicator (though I'm assuming that's because animal companions differ by level). So, I'm not sure how to do the Trample damage. Should it be based on the Gore attack since that's the war bull's only attack?

[Winterschuh]

Then take the damage a creature of that size would deal with a slam attack if it had one.

[Michael Grate]

Winterschuh wrote:

Then take the damage a creature of that size would deal with a slam attack if it had one.

Thank you