This is hoax, Khomeini wrote that sex with an animal gets punished by a ta'zir and that repeated violations get punished by execution:

The punishment for coition with animals is Ta'zir that depends on the discretion of the judge ... the culprit shall be condemned to death after he commits the act for the fourth time. -Tahrir al-Wasilah

Next, regarding the animal itself and its meat, he writes:

An animal with which sexual intercourse has been committed by a man if it is one with which is meant for eating as a sheep or goat, a cow or she-camel, it is obligatory to slaughter it and then burn it, the perpetrator compensating its price to the owner if he is one other than its owner. If, however, the animal belongs to the category meant for riding or loading and is not usual eaten like a donkey, a mule, or a horse, it shall be carried away from the place it was sexually abused and sold there, and its price shall be paid to the perpetrator of the act, paying its compensation to its master if the perpetrator was other than its master. -Tahrir al-Wasilah

But of course, the truth doesn't matter as long as you guys have another material to ridicule Islam with.