My dartmoor pony has milk in her teets, but not in foal?

Ive had my dartmoor pony for years and she has always have relativly big teets. If squeezed, her teets squirt out this sort of milk like liquid. she isnt on lots of grass due to weight and have to be carefull of lamanitis. she has big teets,and always has. Do you think there is a chance when she was wild on the moor that she had a foal, and thats the cause of her teets ?? thankyou :)