Puzzle n°14 (**) - Crossing the River

Three couples (a male and a female) of cats meet on the bank of a river which they want to cross.
There is a couple of persians, a couple of somalis (very much in love with one another) and a couple of rex devon.

They have found a boat without a pilot.
But this boat is so small that it can carry only two cats at a time.

However, none of the males is willing to let males of different breeds go with "his" female...
(Probably their human breeders have had too much influence on them !)
So they must find a way to cross the river such that never any female be with a male of a different breed
if her preferred stud is not around.

How will they manage and what is the minimum number of boat trips this will take ?

... I'm giving up ...