I dont know if the horse liked it Mo, but if the horse was a male, he very may well have. Before people jump down my throat and say I am endorsing sodomy--READ. There is a physiological/anatomical basis for why anal sex is pleasurable for men, and that lay in the role of the prostate. The prostate is a very sensitive organ with hundreds of thousands of nerve endings that when stimulated can result in the male having an orgasm. Female orgasm from anal penetration has a similar physiology, except of course there in no prostate so the nerve endings are connected to stimulation of the anus itself and the resulting stretch on the nerves connected to the vagina.
I AM NOT ENDORSING ANAL SEX, only offering the science behind what makes the practice pleasurable for some.