Nikki began to pant as her horsecock throbbed. "T-turn around." Trish obliged, turning around and moving her tail to display her glistening folds and leathery horse anus. Nikki with a little difficulty climbed atop the centaur and began thrusting her dick into the centaurs behind. Trish waited excitedly for her mare pussy to be penetrated only to instead let out a strained groan as Nikki speared her anus instead. Nikki grunted loudly as her dick was enveloped by the tight warm heat of Trish's anus. "Oh god..Trish!" Nikki moaned out and began thrusting wildly into her hole. Trish began panting and moaning. This might've been even better than getting her cunt railed. Nikki hilted herself as deep as she could get feeling the tip of her cock brush against a tiny bump. As her prostate was stimulated Trish wailed as her dick throbbed and her balls tightened. Trish blasted the ground with a flood white, panting and groaning as her orgasm winded down. As Trish came her ass tightened like a vice around Nikki's dick. Nikki roared as her cock sprayed seed filling Trish's ass. Nikki's cock slipped out of Trish and she hopped down as horse cum trickled down Trish's ass. As Nikki lay on the ground panting in the afterglow of her orgasm she felt a burning heat in her anus and pussy. As she lowered her hand past her balls she felt her cunt shifting and changing. A little further and she found her ass was doing the same. Her lower half now resembled that of a horse anthro.