You heard me before, Yet you hear me again. Then I die, 'Til you call me again What am I?

The Answer

Little farmboy comes in late for school. Teacher asks why he's late. Farmboy replies that he had to take the family cow over to the neighbour's to get her bred by a bull. Annoyed, teacher demands, "Can't your father do that?" Little farm boy thinks for a moment: replies, "Well, sure... but the bull can do it better."