Complex sentence: New Zealand Heading Dogs are extremely intelligent, active dogs with instinct to herd animals; if left alone for too long, they may try to escape and or herd small animals or children.
Split into simpler sentences: New Zealand Heading Dogs are extremely intelligent and should not be left alone for long periods of time. They have the innate ability to herd animals and, if left alone for too long, they will try to escape and or try to herd small animals or children.