sheep creep

noun1

1. •
   A small, low opening built into the base of a drystone wall or farm boundary; it allows sheep and lambs to pass freely between fields while blocking larger livestock like cows.

   • The animal population of the West Highlands had to receive special consideration. No few than 200 creeps were built, ranging from simple wooden sheep-creeps 4 ft wide, to plate girder cattle-creeps — 1914