Animals

• Livestock guardian dog
  Livestock guardian dog
  A livestock guardian dog is a domesticated canine used to defend livestock against predators. LGDs are commonly referred to as "sheep dogs" since they most often have guarded flocks of sheep, but most are capable of guarding other species of livestock. They are classified as pastoral dogs...
  
  , a dog used to guard sheep and other livestock
• Herding dog
  Herding dog
  A herding dog, also known as a stock dog or working dog, is a type of pastoral dog that either has been trained in herding or belongs to breeds developed for herding...
  
  , a dog used to herd sheep and other livestock

Computer science

• Sheepdog a distributed storage system for QEMU/KVM http://www.osrg.net/sheepdog/

Songs

• Sheepdog (song), a song from the album Bring 'Em In by Swedish band Mando Diao