Complex sentence: In one big flock of 650 sheep, four had been killed, but this was due to the shepherds dividing the flock in half during grazing and one half had been left without dogs.
Split into simpler sentences: In one big flock of 650 sheep, four had been killed. Actually, the mistake in that case has been done by the shepherds who had divided the flock in two parts during grazing and one of the two parts had been left without dogs.