The family of a farmer and their cow

There once was a man who lived with his wife and three sons on a farm. They were poor and their whole wealth was a single prized cow. On one morning, the farmer went into to the barn and shockingly found his beloved cow dead on the ground. He couldn't bare telling his family about the loss so he grabed a rope and hung himself.
A few hours later his wife came into the barn and found her husband and the cow both dead. She then took a knife and slit her wrists.
On the next morning the youngest son went looking for his missing parents and after finding them and the cow dead in the barn, he knew he had to relax from the shock, so he took his fishing rod and went to go fishing to the nearby river. After sitting at the river for the whole day, he surprisingly hooked something big and heavy and after reeling it in, he realized it was a beautiful mermaid.
"My dear boy," she said to him "I know about the death of your parents. I have the power to bring them back to life, but in return you have to make love to me."
'Awesome' thought the boy and he went at it. After an hour of intense lovemaking he realized that he was under some sort of spell and the mermaid wouldn't stop humping him. Then, after another hour he died of exhaustion in the middle of the act.
On the next morning the middle-old son also realized that everybody was dead and he also went to the river to go fishing. He also caught the same mermaid and she said the same to him as she did to his younger brother. He accepted her proposition and they began to make love. He lasted twice as long as his younger brother, but in the end he also died of exhaustion.
On the last morning, the oldest son realized everybody was dead and he did the same his sibblings have done. He also caught the very same mermaid and with a grin or her face, she also said the same thing to him. So they began, and after lasting several hours the mermaid thought that this one was quite enduring and that she would take alot out of him. But then the morning came and they were still at it, he lasted the next day and the next night after that. Finally after several days of intense lovemaking the mermaid suddenly collapsed and died of exhaustion. So the young boy stood up, pulled up his pants and thought to himself: 'not bad - but not as good as the cow.'