48 Hours of Hallucinatory Sex (1987)

After seeing the film '24 Horas de Sexo Explícito', Dr Margaret, sexologist hires the same crew to make a new movie, doubling the time - an orgy which would last for 48 hours, to further her research on sex. But as the film progresses it is revealed that she may have an ulterior goal in coaxing her actors into their drugged and sexually frenzied states. Ultimately she persuades a man to dress in an ox costume and penetrate her vaginally while she is naked inside a wooden cow.