It's one of the Muslim forms of unclean sex but still common enough to be mentioned in the Islamic religious texts...
Khomeini's "Tahrirolvasyleh" fourth volume, Darol Elm, Gom, Iran, 1990:
"A man can have sex with sheep, cows and camels and so on. However, he should kill the animal after he has his orgasm. He should not sell the meat to the people in his own village; however, selling the meat to the next door village should be fine."
but a Muslim man can always **** his wife if the goat is a bit off it's feed:
even pedophillia is ok:
"A man can marry a girl younger than nine years of age, even if the girl is still a baby being breastfed. A man, however is prohibited from having intercourse with a girl younger than nine, other sexual acts such as foreplay, rubbing, kissing and sodomy is allowed. A man having intercourse with a girl younger than nine years of age has not committed a crime, but only an infraction, if the girl is not permanently damaged. If the girl, however, is permanently damaged, the man must provide for her all her life. But this girl will not count as one of the man's four permanent wives. He also is not permitted to marry the girl's sister."
Until boys grow a beard they are considered to be bacha bereesh, the same as women. However there are rules concerning the act for example if a Muslim finds a widow and then discovers he desires her 9 year old then he HAS to choose - he can't do both up the dot... The Sahih Collection of al-Bukhari - Book of Marriage - SunniPath
"...As for whom ever plays with a boy: if there is full penetration, then he shall not marry his mother..."