Idea 1
A brilliant, but mad farmer takes vengeance on the woman who betrayed him and the brother she left him for by transforming the now married couple into a goat and cow respectively. The brother struggles to retain his humanity, but the wife suffers far more as her own transformation into a milking goat is paired with her being forced to watch helplessly as her beloved husband is reduced further and further into a mindless cow slut being breed and used by the farms resident bull. No pleas for mercy can sway the farmers wrath and soon all hope will be extinguished for our helpless heroin and her rapidly dimming bovine hubby as they both become breeders for the ranch.
Idea 2
A father and son are captured by a mad scientist who transforms the father into a female cougar before teasing and masturbating her relentlessly all within a hairs breath of the son who is turned into a male cougar. The son struggles with his human disgust and animal desire to breed the tormented female till at last he is forced to eat her out, cementing the animal side as dominant and leading to him fucking his own father. Only in the afterglow is the shame able to fully seep in, just in time for the whole process to begin again.
Voting is over. It looks like idea 2 has no chance... The winner is idea 1!