The researchers found no association between penile cancer and the number of animals the men used over time, the species (which included mares, cows, pigs and chickens, among other animals) or the number of other men who also participated. However, the higher rate of reported sexually transmitted diseases in men who had sex with animals could be a result of group sex, said lead author Stênio de Cássio Zequi, a urologist inSão Paulo. More than 30 percent of subjects practiced SWA in groups.