Complex sentence: The females of most breeds of domestic duck are very unreliable at sitting their eggs and raising their young, and it has been the custom on farms for centuries to put duck eggs under a broody hen for hatching; nowadays s are usually used.
Split into simpler sentences: The females of many breeds of domestic ducks are unreliable at sitting their eggs and raising their young. It has been a custom on farms for centuries to put duck eggs under a broody hen for hatching; nowadays s are usually used.