stado

1. flock; herd
   Pastir čuva stado ovaca na brdu. — The shepherd is watching a flock of sheep on the hill.
   Stado krava prelazilo je put. — A herd of cows was crossing the road.
2. derog. (of people) herd; sheep
   Ljudi se ponašaju kao stado i veruju svemu. — People act like sheep and believe everything.

Stado is used mostly for sheep and goats, while krdo is more often used for horses, cattle and wild animals.