Heart Transplant

A man needing a heart transplant is told by his doctor that the only heart available is that of a sheep. The man finally agrees and the doctor transplants the sheep heart into the man. A few days after the operation, the man comes in for a checkup. The doctor asks him "How are you feeling?" The man replies, "Not BAAAAD!"

Mary Had

Mary had a little sheep, with this sheep, she went to sleep. The sheep turned out to be a ram, and Mary had a little lamb.

Artificial Insemination

A man buys several sheep, hoping to breed them for wool. After several weeks, he notices that none of the sheep are getting pregnant, and calls a veterinarian for help. The vet tells him that he should try artificial insemination.  The guy doesn't have the slightest idea what this means but, not wanting to display his ignorance, only asks the vet how he will know when the sheep are pregnant. The vet tells him that they will stop standing around and will instead lay down and wallow in the grass when they are pregnant.  
The man hangs up and gives it some thought. He comes to the conclusion that artificial insemination means HE has to impregnate the sheep. So, he loads the sheep into his truck, drives them out into the woods, has sex with them all, brings them back and goes to bed.  Next morning, he wakes and looks out at the sheep. Seeing that they are all still standing around, he concludes that the first try didn't take, and loads them in the truck again.  He drives them out to the woods, bangs each sheep twice for good measure, brings them back and goes to bed. The next morning he wakes to find the sheep still just standing around.  One more try, he tells himself, and proceeds to load them up and drive them out to the woods.  He spends all day shagging the sheep and, upon returning home, falls listlessly into bed.  
The next morning, he cannot even raise himself from the bed to look at the sheep.  He asks his wife to look out and tell him if the sheep are laying in the grass.  "No," she says, "they're all in the truck and one of them is honking the horn!"